Telescoped Synthesis of C3-Functionalized (E)-Arylamidines Using Ugi-Mumm and Regiospecific Quinazolinone Rearrangements

Abstract

An efficient four-step, six-transformation protocol was developed to afford bioactive N-alkyl- or N-arylamide (E)-arylamidines featuring strategic amidine C3 modifications which were inaccessible or low yielding by previous methods. This synthetic approach, exemplified with 24 amidines and requiring only a single purification, highlights a multicomponent Ugi-Mumm rearrangement to afford highly diversified quinazolinones which undergo regiospecific rearrangement to afford new amidines. The method extensively broadens the structural scope of this new class of trisubstituted amidines and demonstrates the tolerance of regional C3 amidine steric bulk, visualized with X-ray crystallographic analysis.

Graphical Abstract

An efficient, telescoped, multicomponent assembly and regiospecific rearrangement of highly diversified quinazolinones affords C3 modified, N-aryl- and N-alkylamide arylamidines requiring only a single purification.

Introduction

Trisubstituted amidines are known for a diverse therapeutic range that includes antiarrhythmic,^1a-c anthelmintic,^2a-c antiparasitic,^3a-b antidepressant,^4a-e and antipsychotic^5a-f applications (Fig. 1). Derivatives of the antipsychotic tricyclic amidine, olanzapine, are also reported to be helpful in treating relapsing-remitting forms of multiple sclerosis.⁶

Figure 1.

Drugs of diverse application containing a trisubstituted amidine motif, highlighted in blue

This N’,N,N-trisubstituted amidine motif was revealed to be critical in our discovery and development of novel (E)- amidobenzamidines as potent antiviral agents^7a-b (3, Scheme 1). This unique scaffold originated from a regiospecific rearrangement of chloroalkylquinazolinone 1a treated with 1,2-bis(methylamino)ethane to exclusively yield (E)-amidobenzamidine 3a (Scheme 1). We subsequently reported a one-pot method⁸ by which extended N-Boc-protected amino acids were converted to quinazolinones 1b that could be efficiently transformed into more diverse amidines 3b. Both methods relied on generation of quinazolinone intermediates 1a-b from standard acylation of anthranilic acids, followed by amidation/cyclization.^7a,8,9

Scheme 1.

Previous approaches to N-aryl benzamidines^7a,8

In the context of our anti-infective programs and ongoing synthetic method development, we attempted substitution of the C3 position of benzamidine 3; however, poor yields of C3-modified products were obtained. It was unclear if this was due to steric congestion of substitution at this site or fault of the method. It was also difficult to generate amidobenzamidines bearing N-alkyl substituents on the amide group. While a few N-alkyl substituted amides were made in low yield, it was desirable to construct an array to survey bioactivity. Given the importance of the scaffold to our program and the inadequate synthetic means to regionally diversify it, we sought a method that would comprehensively address these needs. In 2011, Mossetti reported¹⁰ a Ugi-Mumm rearrangement,^11a-h followed by Staudinger/aza-Wittig ring closure^12a-b to generate quinazolinones 6 (Scheme 2). Importantly, these products bore R1 and R2 substituents that would be expected to afford the desired C3-substituted, N-alkyl amide derivatives 8 if a core containing a suitably tethered diamine, as shown in 7, was subjected to our rearrangement conditions.

Scheme 2.

Known Ugi-Mumm quinazolinones and adaptation to N-alkyl amide/C3-substituted amidine construction

The approach potentially offered convenient access to R¹ and R² quinazolinone 7 substitutions and ultimately, potential corresponding substitutions in amidines 8 that were challenging to otherwise incorporate. Furthermore, the Ugi-Mumm-aza-Wittig protocol was furnished as a one-pot method.¹⁰ Nonetheless, limitations of the method as published were also noted. The two-step overall yields for the 13 examples cited were evenly distributed between 40–81%, and use of aryl aldehydes required significantly longer reaction times (3 days). In some cases, Passerini product formation^10,13a-c predominated over desired imide formation in the first step. Additionally, direct use of formaldehyde was not permitted in the Ugi-Mumm reaction, a feature that would limit access to C3-unsubstituted, N-alkyl amides that are important to ongoing projects in our lab. With these pros and cons in mind, we set out to see if this approach could advance our rearrangement strategies and medicinal chemistry goals. Specifically, we aimed to survey a broad range of Ugi substrates and explore the use of problematic Ugi-Mumm partners such as formaldehyde, aryl aldehydes, and heterocyclic azido acids. Importantly, the thrust of this effort was to determine if unique quinazolinones could be efficiently prepared and successfully transformed into novel, C3-substituted amidines to probe unexplored biological space.

Results and Discussion

A brief feasibility study employing published reaction conditions¹⁰ was done using 2-azidobenzoic acid, cyclohexyl- or 4-methoxyphenyl isocyanide, one of three aldehydes of variable steric demand and a requisite mono-N-Boc-protected 1,2-bis(methylamino)ethane 9a used in our rearrangement chemistry (Scheme 3). Key intermediates were isolated to assess the efficiency of each reaction in the sequence. The desired imides 10a-b, resulting from the Ugi-Mumm assembly with cyclohexyl isocyanide and bearing a C3-isopropyl or isobutyl group, were isolated in 83% and 55% yield, respectively (Scheme 3). While some starting material remained, by-products 11a-b were not observed. Formaldehyde was not productive, only affording Passerini α-acyloxy carboximide 11c. Use of 4-methoxyphenyl isocyanide with non-formaldehyde components also generated imides 10d-e in 58–61% yield. Imides 10a-b or 10d-e were individually subjected to Staudinger/aza-Wittig conditions, and afforded corresponding quinazolinones in 60–88% yield. Subsequent TFA treatment to remove the N-Boc protecting group, followed by base-promoted rearrangement gave the amidines in 30–51% yield over two steps. The best outcome for this 4-step, 6-transformation sequence was observed for amidine 13a, isolated in 32% overall yield, corresponded to a 75% average yield per step, and confirmed that a C3-isopropyl group was well tolerated in the quinazolinone rearrangement. We then set out to (a) maximize imide formation, (b) minimize Passerini side reactions, (c) improve quinazolinone and amidine yields, (d) streamline the overall process, and (e) generate diversely functionalized N-alkyl/C3-modified amidines.

Scheme 3.

Pilot chemistry to N-alkyl/C3 modified amidines

Reaction conditions: (a) 2-azidobenzoic acid, R¹NC, R²CHO (1 eq. each), 4 Å MS, CH₂Cl₂, rt, 12 h; (b) PPh₃, toluene, reflux, 12 h; (c) TFA, CH₂Cl₂, 0 °C - rt, 12 h; (d) aq. K₂CO₃, CH₃CN, μW, 150 °C, 1 h. Yields are based on isolated and purified products.

To start, the mechanism of each step was considered (Scheme 4). Fortunately, the historic Ugi, Mumm, Staudinger and aza-Wittig reactions have been substantially reviewed, and mechanisms for each are well documented.^11a-g,12c For our own quinazolinone rearrangement, control experiments were previously executed and published^7a,8 that support the following discussion. Contrary to our previous work in which chloroalkylquinazolinones were prepared by a standard three-step process, this effort required an alternate assembly of the requisite N-alkylamide/C3-substituted amidines (Scheme 4). Specifically, the formation of an iminium ion H between aldehyde A and amine G was a critical part of this effort. Any unreacted aldehyde could participate in a competing three-component Passerini reaction. In that circumstance, isocyanide B adds to the activated aldehyde, forming nitrilium ion C that is intercepted by acid D, forming an O-acylimidate E. Pericyclic acyl transfer then affords undesired α–acyloxy carboxamide F.

Scheme 4.

Mechanistic considerations for a Ugi-Mumm-Staudinger-aza-Wittig- and rearrangement of functionalized quinazolinones leading to N-alkylamide/C3 functionalized arylamidines and avoiding Passerini by-products

In the desired pathway, favoring complete formation of iminium ion H was a priority, as subsequent addition of isocyanide B would irreversibly afford nitrilium ion I and push the process towards the desired outcome. Interception of I with acid D would afford a different O-acylimidate intermediate J; however, in this case, O-to-N-acyl transfer via Mumm rearrangement would provide imide K. Staudinger/aza-Wittig ring closure would form quinazolinone M featuring an N-alkyl amide (R¹), R² substitution from the incorporated aldehyde, and an appended Boc-protected amine of suitable length that, once liberated and rendered basic (O), will undergo rearrangement to amidine Q. Previous work has shown that tethered amines capable of forming a 5- or 6-membered spirocyclic intermediate such as P (latter case shown only), productively affords an amidine. Amine tethers of longer length require formation of unfavored ring sizes and do not rearrange.^7a,8 Attention was first directed to promoting complete imide formation and preventing side reactions (see ESI). Imide 10d formation was used initially to scout reaction parameters. According to the published protocol, equimolar quantities of Ugi-Mumm components were combined concomitantly with molecular sieves in CH₂Cl₂ at ambient temperature.^10,14 We observed that 2-azidobenzoic acid was poorly soluble in CH₂Cl₂, likely contributing to suboptimal conversion. Adding the acid as a 1.0 M solution in 3:1 CH₂Cl₂/CH₃OH resulted in a 10% increase in the isolated imide 10d (68%). This change, in combination with stoichiometric increase of the other reagents to 1.5 equiv. relative to the 2-azidobenzoic acid, improved imide 10d yield (85%), though Passerini product 11d formation was also noted. By implementing these changes and premixing the aldehyde and amine for 6–12 min prior to the addition of acid and isocyanide, Passerini product 11d formation was avoided, and 10d was obtained in 92% yield. Further optimization of stoichiometry revealed that a 2:4:1:4 ratio of diamine:aldehyde:carboxylic acid:isocyanide was ideal, resulting in significantly improved yields across all pilot examples 10a-e, which notably included the first successful direct implementation of formaldehyde (10c, 45%, Scheme 5).Conditions: (a) 9a, R²CHO, 6–12 min, then 2-azidobenzoic acid in 3:1 CH₂Cl₂/CH₃OH, R1NC, (2:4:1:4), 4 Å MS, CH₂Cl₂, rt, 12 h. Yields are based on isolated and purified products.

Scheme 5.

Optimized Ugi-Mumm imide formation

The intramolecular Staudinger/aza-Wittig pilot reactions afforded quinazolinones in reasonable yields (Scheme 3). As such, focus shifted to optimization of the quinazolinone rearrangement. Historically, quinazolinone N-Boc deprotection was effected with TFA (12 h), followed by neutralization with aqueous Na₂CO₃ to promote amidine formation.^7a,8 While productive for substrates not bearing C3 amidine substitution and/or N-alkyl amides, in the present cases, impurities formed in addition to the desired amidines. Resultantly, purification was more complicated and yields were diminished. To address this, we explored other deprotection/base catalyzed conditions. Ultimately, treating 12a with 4M HCl in dioxane for 12 h, followed by microwave irradiation in Et₃N/CH₃OH yielded amidine 13a in 66% yield (45% overall), as compared to 53% (32% overall). With optimized conditions in hand, we sampled a variety of Ugi-Mumm coupling partners to assess efficiency of the stepwise protocol (Table 1). Five aldehydes, ranging in size from formaldehyde to benzaldehyde, were successfully transformed into C3-modified amidines in acceptable yield. This effort revealed that (a) benzaldehyde could be efficiently incorporated in 12 h instead of 3 days, (b) direct use of formaldehyde was feasible and (c) that C3-amidine carbon substitution was reasonably accommodated despite the increased steric demand introduced at this position.

Table 1.

Feasibility assessment and yields for optimized stepwise sequence leading to novel quinazolinones and benzamidines^a,b

Entry	Isocyanide	Aldehyde	Acid	Imide 10a-k		Quinazolinone 12a-k		Benzamidine 13a-k		Overall yield 13a-k (%)
	R1	R2	R3	cmpd	yield (%)	cmpd	yield (%)	cmpd	yield (%)
1	cyclohexyl	isopropyl	H	10a	89	12a	76	13a	66	45
2	cyclohexyl	isobutyl	H	10b	98	12b	60	13b	34	20
3	cyclohexyl	H	H	10c	45	12c	89	13c	58	23
4	4-CH3O-phenyl	isopropyl	H	10d	85	12d	88	13d	23c	17
5	4-CH3O-phenyl	isobutyl	H	10e	78	12e	88	13e	39c	27
6	cyclohexyl	cyclopropyl	H	10f	89	12f	70	13f	65	40
7	cyclohexyl	phenyl	H	10g	97	12g	82	13g	68	54
8	isopropyl	isopropyl	H	10h	88	12h	71	13h	52	32
9	cyclohexyl	isopropyl	5-CH3	10i	78	12i	69	13i	64	34
10	cyclohexyl	isopropyl	5-F	10j	ND	12j	84	13j	40	34
11	cyclohexyl	isopropyl	4-CH3	10k	67	12k	70	13k	61	29

^aConditions: (a) 9a, R²CHO, 6–12 min, then 2-azidobenzoic acid in 3:1 CH₂Cl₂/CH₃OH, R¹NC, (2:4:1:4), 4 Å MS, CH₂Cl₂, rt, 12 h; (b) PPh₃, toluene, rt, 30 min, then 110°C, 12h; (c) 4N HCl, dioxane, 0°C – rt, 12h; (d) Et₃N, CH₃OH, MWI 100°C, 30 min.

^bIsolated yields: avg of n>2 expts.

^c1 h reaction time; ND = not determined, crude material advanced.

We anticipated that yields may be enhanced if the six-transformation sequence could be executed without purification of intermediates.¹⁵ In our estimation, this approach had a good chance of success given that the Mossetti team had demonstrated that their version of the Ugi-Mumm-Staudinger/aza-Wittig sequence could be done without isolation of the imide resulting from the Ugi-Mumm rearrangement.¹⁰ Further, we had reported previously a differentiated telescoped method by which simplified quinazolinones were converted to benzamidines.⁸ Nonetheless, it was uncertain if the new process was amenable to being streamlined in this way, as excess reagents in the Ugi reaction and the new process as a whole introduced by-products that would be carried throughout and may interfere with the efficiency of progressive reactions.

As we assessed this option, it was determined that the presence of triphenylphosphine oxide by-product complicated purification and yields of the reactions following the aza-Wittig reaction. As such, polymer-bound triphenylphosphine was used in the Staudinger/aza-Wittig reaction to simplify end-stage, triphenylphosphine oxide removal.¹⁶ With this change, the undesired by-product was filtered off after the reaction, greatly facilitating work-up and clean isolation of quinazolinone. As such, a telescoped version of the sequence using 2-azidobenzoic acid, isobutyraldehyde, cyclohexylisocyanide and 9a was attempted, affording amidine 13 a in an improved 61% overall yield (versus 45% stepwise) and in 64% yield when executed at 1.0 mmol scale. Amidines 13a-k, first prepared by our stepwise approach at the start of this project, were then generated by the streamlined protocol, revealing an 11–40% improvement in yield (Scheme 6). Encouraged by these results, a more extensive survey of the telescoped protocol was examined. With the exception of 2-azido-6-fluorobenzoic acid and 2-azido-6-methylbenzoic acid, substituted azido benzoic acids¹⁷ were generally well-tolerated throughout the sequence (Scheme 6, 13l-n). Use of these 6-substituted benzoic acids exclusively led to Passerini α–acyloxy carboxamide formation. Presumably, 6-substitution may present significant steric repulsion in the Mumm-rearrangement, thus favoring Passerini by-product formation. Compared to most substituted acids, 2-azido 4-fluorobenzoic acid led to lower yield of amidine 13l (21%, or 68% average yield over 4 steps); however, this starting material was limited by poor solubility.

Scheme 6.

Amidines resulting from a telescoped Ugi-Mumm-Staudinger/aza-Wittig-quinazolinone rearrangement sequence

Introduction of C3 amidine substituents was motivated in part to evaluate the tolerance of regional steric bulk. The absence of (Z)-amidines was attributed to the planar N-amidine substituent that would otherwise clash with the phenyl ring core if a (Z)-configuration was adopted.^7a,8 Introduction of C3 substituents would force the amidine ring to potentially adopt a more extreme puckered and/or twist to accommodate the increased steric bulk. To further test the tolerance of substitution in this region, two analogs were also prepared that featured a methyl group (13m) or a fluorine atom (13n) positioned off of the core phenyl ring which would be oriented Conditions: (a) amine, R²CHO, 6–12 min, then 2-azidobenzoic acid in 3:1 CH₂Cl₂/CH₃OH, R1NC, (2:4:1:4), 4 Å MS, CH₂Cl₂, rt, 12 h; (b) PS-PPh₃, tol, rt, 30 min, then 110°C, 12h; (c) 4N HCl, dioxane, 0°C – rt, 12h; (d) Et₃N, CH₃OH, MWI 100°C, 30 min. Yields: avg of n > 2 expts. Parenthetical yields: stepwise protocol. PMP = p-methoxyphenyl, Cy = cyclohexyl.

towards the amidine C3-substituted isopropyl group. Surprisingly, 3-substituted azido acids, which were expected to yield poorly due to increased regional congestion with C3-substituted isopropyl group, still generated amidines 13m and 13n in 35% and 42% yield, respectively. To understand how C3 substitutions were accommodated, we pursued crystallization of multiple compounds in the set. Fortunately, an X-ray crystal structure of amidine 13t, featuring a C3-positioned phenyl ring, revealed a puckered and twisted amidine ring (Fig. 2). As a result, the amidine N-C double bond is out of the plane of the core phenyl ring, thus allowing the α−amidine substituent to adopt an energetically favorable arrangement relative to the core. Nonetheless, limitations were found. Benzofuran- and benzothiophene-derived azido acids, in combination with cyclopropanecarboxaldehyde, led to isolation of the free-based aminoalkylquinazolinones that would not rearrange to the corresponding amidines even under forcing conditions, likely due to increased steric intolerance. Despite this, smaller heterocyclic azido acids competently rearranged to amidines, 13v-x. Amidines 13u and 13x were generated with unsymmetrical diamines, thereby demonstrating the potential for extensive library generation and incorporation of chiral components.

Figure 2.

Molecular drawing of 13t shown with 50% probability ellipsoids. The conformation of the amidine ring is a distorted envelope the puckering amplitude Q = 0.5488(11) Ang.

Conclusions

The N’,N,N-trisubstituted amidine framework features prominently in a variety of approved drugs with diverse pharmacological value. Having discovered a series of structurally unique, antiviral (E)-amidobenzamidines bearing this motif, we explored a new strategy by which the scaffold could be bi-directionally functionalized. Ultimately, a multicomponent, dual rearrangement strategy was developed that efficiently afforded a diverse assortment of C3-functionalized (E)-arylamidines bearing either N-alkyl or N-aryl amides. As part of this effort, a stepwise approach was first scouted and optimized before refining this process such that only a single, final purification was necessary. By implementing the Ugi-Mumm rearrangement, a broad array of aldehydes, including formaldehyde, was used to deliver novel quinazolinones that transformed into both α-substituted and unsubstituted (E)-arylamidines in moderate to excellent yield over the 4-step, 6-transformation sequence. Further, we demonstrated that the α-amidine position was quite permissive of bulky substituents, a feature visualized with the aid of an X-ray structure of a C3-phenyl derivative. Moreover, heterocycles were successfully incorporated into the amidine scaffold, enriching our understanding of biological targets with which these compounds interact. The compounds are currently being screened across a spectrum of biological assays to evaluate known and orthogonal activity. Results from those studies will detailed separately.

Experimental

General Information

Compounds not described in ESI were purchased from commercial vendors. All synthesized compounds were characterized with the following instrumentation: Varian Unity-Inova 400 MHz NMR spectrometer (operating at 400 and 101 MHz, respectively) or a Varian Unity-Inova 500 MHz NMR spectrometer (operating at 500 and 126 MHz, respectively) in CDCl₃ (CDCl₃: ¹H = δ 7.26 ppm, ¹³C = δ 77.16 ppm). Microwave irradiated (MWI) reactions were carried out using an Anton Paar Monowave 300 Microwave Synthesis Reactor. Flash chromatography separations were carried out using a Teledyne Isco CombiFlash Rf 200 purification system with silica gel columns (normal-phase). High resolution mass spectra (HRMS) were performed by Analytical Instrument Center at the School of Pharmacy on an Electron Spray Injection (ESI) mass spectrometer. Melting points were measured on OptiMelt MPA100 Automated Melting Point System.

General Procedure for the Telescoped Synthesis of C3-Functionalized (E)-Arylamidines

(E)-N-cyclohexyl-2-((3-isopropyl-1,4-dimethylpiperazin-2-ylidene) amino)benzamide 13a.

An oven-dried, 10 mL round bottom flask under nitrogen was charged with activated, powdered, 4 Ǻ molecular sieves (50 mg). The flask was placed under vacuum and flame-dried, then backfilled with nitrogen. N,N′-Dimethylethylenediamine (115 mg, 0.61 mmol, 2.0 equiv.) was dissolved in dry CH₂Cl₂ (0.5 mL, 1.3 M) and added to the reaction vessel. Isobutyraldehyde (112 μL, 1.2 mmol, 4.0 equiv.) was dissolved in dry CH₂Cl₂ (0.46 mL, 2.6 M) in a 1-dram glass vial and added dropwise over 1 min via syringe to the reaction vessel while stirring at rt. Upon completion of the addition, 2-azidobenzoic acid (50 mg, 0.31 mmol, 1.0 equiv.) was dissolved in a 3:1 mixture of dry CH₂Cl₂/MeOH (0.4 mL, 0.8 M), taken up into a syringe and the needle was placed into the septum of the reaction vessel. Cyclohexyl isocyanide (153 μL, 1.2 mmol, 4.0 equiv.) was dissolved in dry CH₂Cl₂ (0.3 mL, 3.6 M) in a 1-dram glass vial, taken up into a syringe and the needle was placed into the septum of the reaction vessel. 2-Azidobenzoic acid was added dropwise to the reaction vessel while stirring over 1 min followed immediately by Cyclohexyl isocyanide. The reaction mixture was stirred at rt for 12 h after which the reaction was complete as judged by complete consumption of carboxylic acid 1 on TLC (10% MeOH/CH₂Cl₂). The crude reaction mixture was filtered through a 0.45 μM syringe filter and the filtrate was concentrated in vacuo. To a flame-dried, 10 mL round bottom flask under nitrogen was added triphenylphosphine on resin (438 mg, 0.61 mmol, 1.4 meq/g, 2.0 equiv.) followed by dry toluene (1.0 mL). A solution of the crude reaction mixture in dry toluene (2.0 mL) was added dropwise and the reaction mixture was stirred at rt for 1 h. After 1 h at rt, the reaction mixture was heated to 110 °C and stirred for 12 h at reflux after which the reaction was complete as judged by complete consumption of the intermediate by TLC (30% EtOAc/hexanes). The crude reaction mixture was filtered through a pad of celite, rinsed with CH₂Cl₂ (10 mL x 5), and the filtrate was concentrated in vacuo. To a flame-dried, 10 mL round bottom flask under nitrogen was dissolved the crude reaction mixture in dry CH₂Cl₂ (3.0 mL, 0.1 M) and the solution cooled to 0 °C in an ice-bath while stirring for 20 min. HCl in dioxane (4.0 M, 0.8 mL, 10.0 equiv.) was added dropwise. The reaction mixture was allowed to slowly warm to rt. The reaction mixture was stirred at rt for 12h after which the reaction was complete as judged by complete consumption of intermediate on TLC (30% EtOAC/hexanes). The reaction mixture was dried in vacuo. Triethylamine (0.4 mL, 3.1 mmol, 10.0 equiv.) was added to a solution of the crude reaction mixture in MeOH (3.1 mL, 0.1 M) in a 10 mL microwave vial and the reaction mixture was heated in a microwave reactor at 100 °C for 1 h. The reaction mixture was allowed to cool to rt and the solvent was removed in vacuo. The crude mixture was dissolved in CH₂Cl₂ (10 mL) and washed with water (10 mL), then saturated brine solution (10 mL), The organic layer was dried over MgSO₄, filtered and concentrated in vacuo. The crude residue was purified by normal-phase chromatography (0–60% EtOAc/Hex) to yield the benzamidine, 13a (69 mg, 61%) as a pale-yellow oil. ¹H NMR (500 MHz, CDCl₃) δ 8.93 (d, J = 8.0 Hz, 1H), 8.17 (dd, J = 7.9, 1.7 Hz, 1H), 7.28 – 7.24 (m, 1H), 7.05 – 7.01 (m, 1H), 6.59 (dd, J = 7.8, 1.2 Hz, 1H), 3.95 (tdt, J = 11.5, 7.9, 3.9 Hz, 1H), 3.47 – 3.39 (m, 2H), 3.36 (ddd, J = 12.3, 7.1, 4.6 Hz, 1H), 3.23 (ddd, J = 11.9, 7.0, 4.4 Hz, 1H), 3.11 (s, 3H), 2.63 (ddd, J = 12.0, 6.6, 4.7 Hz, 1H), 2.49 (s, 3H), 2.07 – 1.97 (m, 2H), 1.76 – 1.69 (m, 3H), 1.68 – 1.61 (m, 1H), 1.38 (ddt, J = 17.9, 12.8, 6.4 Hz, 2H), 1.21 – 1.10 (m, 3H), 0.79 (d, J = 6.7 Hz, 3H), 0.63 (d, J = 6.9 Hz, 3H); ¹³C NMR (126 MHz, CDCl₃) δ 165.9, 160.5, 148.5, 131.2, 131.1, 125.8, 122.4, 122.0, 63.9, 48.7, 48.4, 47.8, 45.0, 37.4, 33.8, 33.7, 32.4, 25.9, 25.3, 20.1, 19.2; HRMS (ESI): Calculated for C₂₂H₃₄N₄O (M++H): 371.28054; Found: 371.28091.

(E)-N-cyclohexyl-2-((3-isobutyl-1,4-dimethylpiperazin-2-ylidene)amino)benzamide 13b.

Obtained using isovaleraldehyde following general procedure. Purified by normal-phase chromatography (0–10% MeOH/CH₂Cl₂) to yield the benzamidine, 13b (71 mg, 60%) as a pale-yellow gum. ¹H NMR (400 MHz, CDCl₃) δ 8.56 (d, J = 8.1 Hz, 1H), 8.18 (dd, J = 7.9, 1.6 Hz, 1H), 7.30 – 7.25 (m, 2H), 7.05 (td, J = 7.6, 1.1 Hz, 1H), 6.61 (dd, J = 7.8, 1.1 Hz, 1H), 3.97 (dddd, J = 14.6, 10.6, 7.9, 3.9 Hz, 1H), 3.61 (td, J = 11.8, 5.3 Hz, 1H), 3.49 (dd, J = 10.6, 3.7 Hz, 1H), 3.41 (ddd, J = 14.0, 11.7, 5.2 Hz, 1H), 3.12 (ddd, J = 12.1, 5.3, 1.7 Hz, 1H), 3.08 (s, 3H), 2.73 – 2.66 (m, 1H), 2.50 (s, 3H), 2.02 – 1.94 (m, 2H), 1.71 (dq, J = 11.7, 4.0 Hz, 2H), 1.63 (dt, J = 12.6, 3.8 Hz, 1H), 1.54 (ddd, J = 14.1, 10.6, 3.9 Hz, 1H), 1.49 – 1.34 (m, 3H), 1.16 (dddd, J = 26.0, 15.5, 12.6, 5.6 Hz, 3H), 0.91 (ddd, J = 13.6, 9.7, 3.6 Hz, 1H), 0.66 (d, J = 6.6 Hz, 3H), 0.27 (d, J = 6.5 Hz, 3H). ¹³C NMR (101 MHz, CDCl₃) δ 165.7, 161.8, 148.6, 131.4, 131.3, 125.6, 122.9, 122.4, 56.8, 48.2, 44.9, 43.8, 42.2, 40.1, 37.3, 33.8, 33.6, 25.9, 25.1, 25.1, 24.4, 23.4, 20.3. HRMS (ESI): Calculated for C₂₃H₃₆N₄O (M++H): 385.29619; Found: 385.29719.

(E)-2-((3-isopropyl-1,4-dimethylpiperazin-2-ylidene)amino)-N-(4-methoxyphenyl)benzamide 13d.

Obtained using 4-methoxyphenyl isocyanide following general procedure. Purified by normal-phase chromatography (0–10% MeOH/CH₂Cl₂) to yield the benzamidine, 13d (120mg, 40%) as a pale-yellow waxy solid. ¹H NMR (400 MHz, CDCl₃) δ 10.97 (s, 1H), 8.24 (dd, J = 8.0, 1.7 Hz, 1H), 7.53 (d, J = 8.5 Hz, 2H), 7.36 – 7.29 (m, 1H), 7.09 (t, J = 7.6 Hz, 1H), 6.88 (d, J = 8.7 Hz, 2H), 6.67 (d, J = 7.9 Hz, 1H), 3.79 (d, J = 1.3 Hz, 3H), 3.46 – 3.35 (m, 3H), 3.27 – 3.21 (m, 1H), 3.19 (s, 3H), 2.63 (dt, J = 11.9, 5.7 Hz, 1H), 2.52 (s, 3H), 1.75 (h, J = 6.8 Hz, 1H), 0.77 (d, J = 6.7 Hz, 3H), 0.65 (d, J = 6.8 Hz, 3H). ¹³C NMR (101 MHz, CDCl₃) δ 165.0, 161.0, 156.1, 148.6, 132.0, 131.7, 131.3, 125.9, 122.6, 122.3, 122.0, 114.3, 64.0, 55.6, 48.3, 47.7, 44.9, 37.6, 32.5, 20.0, 19.3. HRMS (ESI): Calculated for C₂₃H₃₀N₄O₂ (M++H): 395.24415; Found: 395.24443.

(E)-2-((3-isobutyl-1,4-dimethylpiperazin-2-ylidene)amino)-N-(4-methoxyphenyl)benzamide 13e.

Obtained using isovaleraldehyde and 4-methoxyphenyl isocyanide following general procedure. Purified by normal-phase chromatography (0–20% EtOAc/CH₂Cl₂) to yield the benzamidine, 13e (56 mg, 45%) as a light-brown solid. m.p.: 109–111°C. ¹H NMR (400 MHz, CDCl₃) δ 10.68 (s, 1H), 8.25 (dd, J = 8.0, 1.7 Hz, 1H), 7.62 – 7.50 (m, 2H), 7.34 (td, J = 7.6, 1.7 Hz, 1H), 7.19 – 7.06 (m, 1H), 6.94 – 6.85 (m, 2H), 6.76 – 6.64 (m, 1H), 3.80 (s, 3H), 3.61 (ddd, J = 12.4, 8.8, 4.4 Hz, 2H), 3.38 (ddd, J = 14.0, 11.6, 5.3 Hz, 1H), 3.18 (s, 3H), 3.11 (ddd, J = 12.1, 5.4, 1.7 Hz, 1H), 2.69 (dd, J = 14.3, 5.1 Hz, 1H), 2.50 (s, 3H), 1.56 (ddd, J = 14.0, 10.6, 3.7 Hz, 1H), 1.47 (dqd, J = 10.4, 6.6, 3.9 Hz, 0H), 0.92 (ddd, J = 13.5, 9.7, 3.5 Hz, 1H), 0.65 (d, J = 6.7 Hz, 3H), 0.28 (d, J = 6.5 Hz, 3H). ¹³C NMR (101 MHz, CDCl₃) δ 164.6, 162.2, 155.9, 148.5, 132.1, 131.7, 131.3, 125.6, 123.0, 122.5, 121.6, 114.2, 77.4, 77.0, 76.7, 56.8, 55.5, 44.7, 43.4, 42.1, 39.9, 37.3, 24.4, 23.3, 20.2. HRMS (ESI): Calculated for C₂₄H₃₂N₄O₂ (M++H): 409.25980; Found: 409.25931.

(E)-N-cyclohexyl-2-((3-cyclopropyl-1,4-dimethylpiperazin-2-ylidene)amino)benzamide 13f.

Obtained using cyclopropanecarboxaldehyde following general procedure. Purified by normal-phase chromatography (0–5% MeOH/CH₂Cl₂) to yield amidine 13f (80 mg, 70%) as a pale-yellow gum. ¹H NMR (400 MHz, CDCl₃) δ 8.62 (d, J = 8.1 Hz, 1H), 8.18 (dt, J = 7.9, 1.5 Hz, 1H), 7.28 – 7.21 (m, 1H), 7.09 – 7.01 (m, 1H), 6.56 (d, J = 7.8 Hz, 1H), 3.96 (dtt, J = 11.2, 7.8, 4.1 Hz, 1H), 3.58 – 3.44 (m, 2H), 3.30 (dd, J = 10.3, 4.2 Hz, 1H), 3.09 (s, 3H), 2.92 (d, J = 8.6 Hz, 1H), 2.76 (dd, J = 11.8, 4.6 Hz, 1H), 2.46 (s, 3H), 1.98 (d, J = 12.9 Hz, 2H), 1.78 – 1.62 (m, 4H), 1.41 (qd, J = 12.5, 6.0 Hz, 3H), 1.23 – 1.06 (m, 3H), 0.90 (ddt, J = 13.8, 8.8, 4.3 Hz, 1H), 0.40 (td, J = 8.7, 4.5 Hz, 1H), 0.28 (tt, J = 8.6, 5.4 Hz, 1H). ¹³C NMR (101 MHz, CDCl₃) δ 165.8, 160.4, 148.9, 131.3, 131.1, 126.4, 122.6, 122.3, 62.1, 48.3, 47.4, 45.5, 42.3, 37.3, 33.8, 33.7, 25.9, 25.2, 25.2, 11.6, 4.1, 3.7, 1.2. HRMS (ESI): Calculated for C₂₂H₃₂N₄O (M++H): 369.26489; Found: 369.26570.

(E)-N-cyclohexyl-2-((1,4-dimethyl-3-phenylpiperazin-2-ylidene)amino)benzamide 13g.

Obtained using benzaldehyde following general procedure. Purified by normal-phase chromatography (0–10% MeOH/CH₂Cl₂) to yield benzamidine, 13g (85 mg, 68%) as a pale-yellow gum. ¹H NMR (500 MHz, CDCl₃) δ 8.36 (d, J = 7.7 Hz, 1H), 7.88 (dd, J = 7.9, 1.5 Hz, 1H), 7.18 (t, J = 7.4 Hz, 1H), 7.11 (t, J = 7.5 Hz, 2H), 7.08 – 7.03 (m, 1H), 6.93 – 6.89 (m, 1H), 6.85 (d, J = 7.2 Hz, 2H), 6.37 (d, J = 7.7 Hz, 1H), 4.41 (s, 1H), 3.86–3.83 (m, 1H), 3.57 – 3.51 (m, 2H), 3.24 (s, 3H), 3.03 – 2.95 (m, 1H), 2.62–2.58 (m, 1H), 2.16 (s, 3H), 2.05 – 1.94 (m, 2H), 1.80 – 1.69 (m, 2H), 1.68–1.584 (m, 1H), 1.46 – 1.34 (m, 2H), 1.23 – 1.11 (m, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 165.3, 165.2, 157.6, 148.1, 135.7, 130.8, 130.6, 129.3, 128.0, 127.9, 125.5, 123.2, 122.1, 65.3, 49.1, 48.3, 46.6, 42.1, 37.4, 33.7, 33.7, 25.9, 25.2, 25.2. HRMS (ESI): Calculated for C₂₅H₃₂N₄O (M++H): 405.26489; Found: 405.26680.

(E)-N-isopropyl-2-((3-isopropyl-1,4-dimethylpiperazin-2-ylidene)amino)benzamide 13h.

Obtained using isopropyl isocyanide following general procedure. Purified by normal-phase chromatography (0–5% MeOH/CH₂Cl₂) to yield the benzamidine, 13h (51 mg, 50%) as a pale-yellow oil. ¹H NMR (500 MHz, CDCl₃) δ 8.94 (d, J = 7.6 Hz, 1H), 8.18 (dd, J = 7.9, 1.6 Hz, 1H), 7.28 (dd, J = 7.5, 1.7 Hz, 1H), 7.06 – 7.02 (m, 1H), 6.60 (dd, J = 7.9, 1.2 Hz, 1H), 4.31 – 4.22 (m, 1H), 3.48 – 3.41 (m, 2H), 3.36 (ddd, J = 12.2, 7.0, 4.6 Hz, 1H), 3.24 (ddd, J = 11.8, 7.0, 4.4 Hz, 1H), 3.13 (s, 3H), 2.64 (ddd, J = 12.0, 6.7, 4.7 Hz, 1H), 2.50 (s, 3H), 1.72 (h, J = 6.7 Hz, 1H), 1.22 (d, J = 6.5 Hz, 6H), 0.80 (d, J = 6.7 Hz, 3H), 0.64 (d, J = 6.8 Hz, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 166.0, 160.5, 148.6, 131.3, 131.2, 125.8, 122.4, 122.1, 64.0, 48.8, 47.9, 45.1, 41.3, 37.3, 32.5, 23.3, 23.2, 20.2, 19.3. HRMS (ESI): Calculated for C₁₉H₃₀N₄O (M++H): 331.24924; Found: 331.24986.

(E)-N-cyclohexyl-2-((3-isopropyl-1,4-dimethylpiperazin-2-ylidene)amino)-5-methylbenzamide 13i.

Obtained using 2-azido-5-methylbenzoic acid following general procedure. Purified by normal-phase chromatography (0–5% MeOH/CH₂Cl₂) to yield the benzamidine, 13i (53 mg, 45%) as a pale-yellow oil. ¹H NMR (400 MHz, CDCl₃) δ 8.90 (d, J = 8.1 Hz, 1H), 7.96 (d, J = 2.2 Hz, 1H), 7.06 (dd, J = 8.0, 2.2 Hz, 1H), 6.49 (d, J = 8.0 Hz, 1H), 3.93 (tdt, J = 11.4, 7.8, 3.9 Hz, 1H), 3.48 – 3.36 (m, 2H), 3.34 (ddd, J = 12.0, 7.0, 4.6 Hz, 1H), 3.22 (ddd, J = 11.8, 7.0, 4.5 Hz, 1H), 3.09 (s, 3H), 2.62 (ddd, J = 11.9, 6.6, 4.7 Hz, 1H), 2.48 (s, 3H), 2.30 (s, 3H), 2.07 – 1.94 (m, 3H), 1.73 (ddt, J = 11.9, 8.0, 4.5 Hz, 2H), 1.71 – 1.58 (m, 1H), 1.38 (tdt, J = 16.5, 12.1, 3.8 Hz, 2H), 1.13 (qdt, J = 10.6, 6.7, 3.2 Hz, 3H), 0.79 (d, J = 6.7 Hz, 3H), 0.63 (d, J = 6.9 Hz, 3H). ¹³C NMR (101 MHz, CDCl₃) δ 166.1, 160.6, 146.0, 131.9, 131.5, 125.5, 122.3, 64.0, 48.7, 48.5, 47.9, 45.0, 37.4, 33.8, 33.8, 32.5, 25.9, 25.3, 20.8, 20.1, 19.3. HRMS (ESI): Calculated for C₂₃H₃₆N₄O (M++H): 385.29619; Found: 385.29605.

(E)-N-cyclohexyl-5-fluoro-2-((3-isopropyl-1,4-dimethylpiperazin-2-ylidene)amino)benzamide 13j.

Obtained using 2-azido-5-fluorobenzoic acid following general procedure. Purified by normal-phase chromatography (0–5% MeOH/CH₂Cl₂) to yield the benzamidine, 13j (67 mg, 56%) as a pale-yellow gum. ¹H NMR (400 MHz, CDCl₃) δ 8.99 (d, J = 7.4 Hz, 1H), 7.90 (dd, J = 10.1, 2.9 Hz, 1H), 6.99 (td, J = 8.4, 3.1 Hz, 1H), 6.56 (dd, J = 8.6, 4.9 Hz, 1H), 4.03 – 3.87 (m, 1H), 3.48–3.46 (m, 1H), 3.41 – 3.31 (m, 2H), 3.28–3.22 (m, 1H), 3.13 (s, 3H), 2.70 – 2.60 (m, 1H), 2.50 (s, 3H), 2.10 – 1.95 (m, 2H), 1.80 – 1.59 (m, 4H), 1.51 – 1.35 (m, 2H), 1.24–1.18 (m, 3H), 0.81 (d, J = 6.7 Hz, 3H), 0.65 (d, J = 6.8 Hz, 3H). 19F NMR (376 MHz, CDCl₃) δ −122.09. ¹³C NMR (101 MHz, CDCl₃) δ 164.6, 164.6, 160.9, 159.6, 157.2, 149.9, 127.1, 127.1, 123.5, 123.4, 118.1, 117.8, 117.3, 117.1, 63.9, 48.7, 48.6, 47.8, 45.1, 37.3, 33.7, 33.6, 32.5, 25.8, 25.2, 20.0, 19.1. HRMS (ESI): Calculated for C₂₂H₃₃FN₄O (M++H): 389.27112; Found: 389.27059.

(E)-N-cyclohexyl-2-((3-isopropyl-1,4-dimethylpiperazin-2-ylidene)amino)-4-methylbenzamide 13k.

Obtained using 2-azido-4-methylbenzoic acid following general procedure. Purified by normal-phase chromatography (0–5% MeOH/CH₂Cl₂) to yield the benzamidine, 13k (53 mg, 45%) as a pale-yellow gum. ¹H NMR (400 MHz, CDCl₃) δ 8.84 (d, J = 8.0 Hz, 1H), 8.06 (d, J = 8.0 Hz, 1H), 6.84 (d, J = 8.0 Hz, 1H), 6.39 (s, 1H), 3.94 (dtd, J = 11.3, 7.6, 4.1 Hz, 1H), 3.49 – 3.30 (m, 3H), 3.23 (ddd, J = 11.8, 6.9, 4.5 Hz, 1H), 3.10 (s, 3H), 2.63 (ddd, J = 12.0, 6.7, 4.7 Hz, 1H), 2.50 (s, 3H), 2.29 (s, 3H), 2.01 (tt, J = 8.4, 3.8 Hz, 2H), 1.78 – 1.59 (m, 4H), 1.46 – 1.31 (m, 2H), 1.21 – 1.06 (m, 3H), 0.80 (d, J = 6.7 Hz, 3H), 0.64 (d, J = 6.8 Hz, 3H). ¹³C NMR (101 MHz, CDCl₃) δ 166.0, 160.5, 148.4, 141.3, 131.3, 123.3, 123.1, 123.0, 64.1, 48.8, 48.4, 47.9, 45.01, 37.4, 33.9, 33.8, 32.6, 25.9, 25.3, 21.4, 20.1, 19.4. HRMS (ESI): Calculated for C₂₃H₃₆N₄O (M++H): 385.29619; Found: 385.29585.

(E)-N-cyclohexyl-4-fluoro-2-((3-isopropyl-1,4-dimethylpiperazin-2-ylidene)amino)benzamide 13l.

Obtained using 2-azido-4-fluorobenzoic acid following general procedure. Purified by normal-phase chromatography (0–40% EtOAc/hexane) to yield the benzamidine, 13l (25mg, 21%) as a pale-yellow gum. ¹H NMR (400 MHz, CDCl₃) δ 8.81 (d, J = 8.0 Hz, 1H), 8.19 (dd, J = 8.8, 7.1 Hz, 1H), 6.73 (td, J = 8.4, 2.5 Hz, 1H), 6.30 (dd, J = 10.3, 2.5 Hz, 1H), 3.94 (tdt, J = 11.5, 7.9, 3.9 Hz, 1H), 3.52 – 3.42 (m, 2H), 3.37 (ddd, J = 12.3, 6.8, 4.7 Hz, 1H), 3.24 (ddd, J = 11.7, 6.8, 4.5 Hz, 1H), 3.13 (s, 3H), 2.65 (ddd, J = 12.0, 6.8, 4.7 Hz, 1H), 2.52 (s, 3H), 2.02 (dt, J = 11.8, 4.1 Hz, 2H), 1.70 (ddt, J = 29.4, 14.9, 5.2 Hz, 5H), 1.40 (qd, J = 12.5, 3.3 Hz, 2H), 1.22 – 1.06 (m, 3H), 0.82 (d, J = 6.7 Hz, 3H), 0.68 (d, J = 6.9 Hz, 3H). 19F NMR (376 MHz, CDCl₃) δ −109.97. ¹³C NMR (101 MHz, CDCl₃) δ 165.2, 165.0, 162.7, 160.8, 150.5, 150.4, 133.5, 133.4, 122.2, 122.2, 108.9, 108.7, 108.6, 108.4, 63.8, 48.6, 48.4, 47.7, 45.1, 37.3, 33.8, 33.7, 32.5, 29.7, 25.8, 25.2, 20.1, 19.1. HRMS (ESI): Calculated for C₂₂H₃₃FN₄O (M++H): 389.27116; Found: 389.27155.

(E)-N-cyclohexyl-2-((3-isopropyl-1,4-dimethylpiperazin-2-ylidene)amino)-3-methylbenzamide 13m.

Obtained using 2-azido-3-methylbenzoic acid following general procedure. Purified by normal phase chromatography (0–30% EtoAc/CH₂Cl₂) to yield the benzamidine, 13m (41 mg, 35%) as a pale-yellow oil. ¹H NMR (400 MHz, CDCl₃) δ 8.66 (d, J = 7.9 Hz, 1H), 8.04 (dd, J = 7.9, 1.6 Hz, 1H), 7.23 (dd, J = 7.4, 1.5 Hz, 1H), 6.97 (t, J = 7.6 Hz, 1H), 3.92 (dtt, J = 11.6, 8.0, 4.0 Hz, 1H), 3.60 (ddd, J = 12.6, 9.6, 3.2 Hz, 1H), 3.20 (s, 4H), 3.13 (s, 1H), 3.05 (ddd, J = 15.4, 8.6, 3.7 Hz, 1H), 2.94 (d, J = 3.0 Hz, 1H), 2.62 (ddd, J = 11.4, 9.6, 3.6 Hz, 1H), 2.38 (s, 3H), 2.11 (d, J = 3.8 Hz, 4H), 2.07 – 1.94 (m, 1H), 1.72 (tdd, J = 12.8, 8.1, 5.1 Hz, 1H), 1.63 (qd, J = 7.0, 3.0 Hz, 1H), 1.49 – 1.30 (m, 2H), 1.14 (tddd, J = 11.6, 8.7, 6.3, 3.8 Hz, 3H), 0.83 (d, J = 6.9 Hz, 3H), 0.67 (d, J = 6.9 Hz, 4H). ¹³C NMR (101 MHz, CDCl₃) δ 166.1, 160.5, 147.5, 133.2, 129.1, 127.8, 126.0, 121.6, 65.8, 51.5, 49.0, 48.4, 47.4, 37.2, 33.8, 33.7, 32.8, 25.8, 25.3, 25.2, 21.2, 19.2, 17.6. HRMS (ESI): Calculated for C₂₂H₃₃FN₄O (M++H): 389.27112; Found: 389.27196.

(E)-N-cyclohexyl-3-fluoro-2-((3-isopropyl-1,4-dimethylpiperazin-2-ylidene)amino)benzamide 13n.

Obtained using 2-azido-3-fluorobenzoic acid following general procedure. Purified by normal-phase chromatography (0–15% EtOAc/CH₂Cl₂) to yield the benzamidine, 13n (65 mg, 42%) as a pale-yellow gum. ¹H NMR (400 MHz, CDCl₃) δ 9.00 (s, 1H), 7.99 (d, J = 7.9 Hz, 1H), 7.10 (ddd, J = 10.1, 8.0, 1.6 Hz, 1H), 6.94 (td, J = 8.0, 5.1 Hz, 1H), 3.94 (tdt, J = 11.4, 7.8, 3.8 Hz, 1H), 3.51 (ddd, J = 12.1, 8.0, 3.8 Hz, 1H), 3.33 (ddd, J = 12.6, 5.9, 4.1 Hz, 1H), 3.19 (s, 3H), 3.12 (t, J = 3.2 Hz, 2H), 2.66 (ddd, J = 12.1, 8.0, 4.1 Hz, 1H), 2.45 (s, 3H), 2.07 – 1.97 (m, 2H), 1.77 – 1.61 (m, 4H), 1.46 – 1.34 (m, 2H), 1.16 (dddd, J = 12.4, 8.6, 6.8, 2.7 Hz, 3H), 0.82 (d, J = 6.8 Hz, 3H), 0.70 (d, J = 6.9 Hz, 3H). 19F NMR (376 MHz, CDCl₃) δ −127.01. ¹³C NMR (101 MHz, CDCl₃) δ 165.1, 162.9, 153.8, 151.4, 137.2, 137.1, 127.9, 126.7, 121.4, 121.4, 118.0, 117.8, 66.0, 49.9, 48.6, 48.3, 46.0, 37.5, 33.8, 33.7, 33.6, 29.8, 25.9, 25.3, 20.6, 18.7. HRMS (ESI): Calculated for C₂₂H₃₃FN₄O (M++H): 389.27112; Found: 389.27196.

(E)-5-cyano-2-((3-cyclopropyl-1,4-dimethylpiperazin-2-ylidene)amino)-N-isopropylbenzamide 13o.

Obtained using cyclopropanecarboxaldehyde, 2-azido-5-cyanobenzoic acid and isopropyl isocyanide following general procedure. Purified by normal-phase chromatography (0–15% MeOH/EtOAC) to yield the benzamidine, 13o (48 mg, 44%) as a light-brown solid. m.p.: 147–148°C. ¹H NMR (400 MHz, CDCl₃) δ 8.61 (d, J = 7.7 Hz, 1H), 8.52 (d, J = 2.1 Hz, 1H), 7.50 (dd, J = 8.2, 2.1 Hz, 1H), 6.62 (d, J = 8.2 Hz, 1H), 4.32 – 4.18 (m, 1H), 3.58 (td, J = 11.0, 5.5 Hz, 1H), 3.45 (ddd, J = 12.8, 10.4, 5.1 Hz, 1H), 3.35 (ddd, J = 11.7, 5.1, 2.4 Hz, 1H), 3.13 (s, 3H), 2.93 (d, J = 8.4 Hz, 1H), 2.79 (ddd, J = 13.2, 5.7, 2.3 Hz, 1H), 2.46 (s, 3H), 1.23 (d, J = 6.6 Hz, 3H), 1.20 (d, J = 6.5 Hz, 3H), 0.89 (dtd, J = 13.3, 8.3, 5.0 Hz, 1H), 0.51 – 0.40 (m, 1H), 0.36 – 0.25 (m, 1H), 0.14 (dq, J = 10.5, 5.2 Hz, 1H), −0.48 (dq, J = 10.3, 5.2 Hz, 1H). ¹³C NMR (101 MHz, CDCl₃) δ 163.8, 160.6, 153.0, 135.7, 134.2, 126.8, 123.3, 119.2, 105.0, 61.9, 47.2, 45.3, 42.3, 41.4, 37.2, 23.1, 23.0, 11.5, 3.9, 3.6. HRMS (ESI): Calculated for C₂₀H₂₇N₅O (M++H): 354.22884; Found: 354.22999.

(E)-2-((3-isopropyl-1,4-dimethylpiperazin-2-ylidene)amino)-N-(4-methoxyphenyl)-5-nitrobenzamide 13p.

Obtained using 2-azido-5-nitrobenzoic acid 4-methoxyphenyl isocyanide following general procedure. Purified by normal-phase chromatography (0–3% EtOAc/CH₂Cl₂) to yield the benzamidine, 13p (49 mg, 36%) as yellow solid. m.p.: 167–168°C. ¹H NMR (400 MHz, CDCl₃) δ 10.93 (s, 1H), 9.17 (d, J = 2.8 Hz, 1H), 8.16 (dd, J = 8.8, 2.9 Hz, 1H), 7.59 – 7.46 (m, 2H), 6.97 – 6.84 (m, 2H), 6.71 (d, J = 8.8 Hz, 1H), 3.81 (s, 3H), 3.57 – 3.46 (m, 2H), 3.45 (d, J = 6.4 Hz, 1H), 3.27 (s, 4H), 2.76 – 2.65 (m, 1H), 2.55 (s, 3H), 1.76 (h, J = 6.7 Hz, 1H), 0.80 (d, J = 6.7 Hz, 3H), 0.70 (d, J = 6.8 Hz, 3H). ¹³C NMR (101 MHz, CDCl₃) δ 162.5, 162.0, 156.3, 154.3, 142.3, 131.3, 127.8, 126.4, 125.7, 122.6, 121.8, 114.3, 64.3, 55.5, 48.0, 47.5, 44.9, 37.8, 32.8, 20.0, 19.1. Calculated for HRMS (ESI): C₂₃H₂₉N₅O₄ (M++H): 440.22923; Found: 440.22903.

(E)-N-isopropyl-2-((3-isopropyl-1,4-dimethylpiperazin-2-ylidene)amino)-5-nitrobenzamide 13q.

Obtained using 2-azido-5-nitrobenzoic acid and isopropyl isocyanide following general procedure. Purified by normal-phase chromatography (0–7% EtOAc/CH₂Cl₂) to yield the benzamidine, 13q (36 mg, 31%) as a yellow-orange solid. m.p.: 140–141°C. ¹H NMR (400 MHz, CDCl₃) δ 9.10 (d, J = 2.8 Hz, 1H), 8.93 (d, J = 7.6 Hz, 1H), 8.12 (dd, J = 8.8, 2.9 Hz, 1H), 6.65 (d, J = 8.8 Hz, 1H), 4.27 (dq, J = 13.2, 6.5 Hz, 1H), 3.53 (ddd, J = 11.9, 6.9, 4.5 Hz, 1H), 3.46 (dd, J = 6.7, 4.9 Hz, 1H), 3.42 (d, J = 6.0 Hz, 1H), 3.25 (ddd, J = 12.6, 6.6, 4.5 Hz, 1H), 3.19 (s, 3H), 2.71 (ddd, J = 12.1, 6.9, 4.8 Hz, 1H), 2.53 (s, 3H), 1.71 (h, J = 6.7 Hz, 1H), 1.23 (dd, J = 6.6, 1.4 Hz, 6H), 0.83 (d, J = 6.7 Hz, 3H), 0.69 (d, J = 6.8 Hz, 3H). ¹³C NMR (101 MHz, CDCl₃) δ 163.7, 161.3, 154.4, 142.0, 127.68, 126.0, 125.6, 122.5, 77.4, 77.0, 76.7, 64.2, 48.5, 47.7, 45.1, 41.6, 37.4, 32.9, 23.02, 23.0, 20.1, 19.0. Calculated for HRMS (ESI): C₁₉H₂₉N₅O₃ (M++H): 376.23432; Found: 376.23487.

(E)-N-cyclohexyl-2-((1,4-dimethyl-3-(thiazol-5-yl)piperazin-2-ylidene)amino)benzamide 13r.

Obtained using 5-thiazolecarboxaldehyde following general procedure. Purified by normal-phase chromatography (0.5–3.5% MeOH/CH₂Cl₂) to yield the benzamidine, 13r (76 mg, 60%) as an amber gum. ¹H NMR (400 MHz, CDCl₃) δ 8.70 (s, 1H), 8.05 (d, J = 7.9 Hz, 1H), 7.99 (dd, J = 7.9, 1.7 Hz, 1H), 7.30 (s, 1H), 7.15 (td, J = 7.6, 1.7 Hz, 1H), 7.06 – 6.99 (m, 1H), 6.38 (d, J = 7.8 Hz, 1H), 4.86 (s, 1H), 3.87 (dtd, J = 10.9, 7.4, 4.0 Hz, 1H), 3.55 (td, J = 11.0, 5.1 Hz, 1H), 3.38 (ddd, J = 11.5, 4.6, 2.7 Hz, 1H), 3.18 (s, 3H), 2.97 (ddd, J = 12.6, 10.6, 4.6 Hz, 1H), 2.64 (ddd, J = 12.9, 5.3, 2.4 Hz, 1H), 2.17 (s, 3H), 2.03 – 1.94 (m, 2H), 1.79 – 1.61 (m, 5H), 1.46 – 1.32 (m, 1H), 1.16 (dq, J = 14.3, 11.5, 11.0 Hz, 3H). ¹³C NMR (101 MHz, CDCl₃) δ 165.1, 156.3, 153.5, 147.3, 143.9, 131.1, 131.0, 130.9, 125.8, 122.8, 122.6, 56.5, 49.2, 48.4, 45.8, 41.6, 37.3, 33.6, 25.8, 25.1. HRMS (ESI): Calculated for C₂₂H₂₉N₅OS (M++H): 412.21656; Found: 412.21798.

(E)-N-cyclohexyl-3-((1,4-dimethyl-3-phenylpiperazin-2-ylidene)amino)-2-naphthamide 13s.

Obtained using benzaldehyde and 3-azido-2-naphthanoic acid following general procedure. Purified by normal-phase chromatography (0–20% EtOAc/CH₂Cl₂) to yield the naphthamidine, 13s (69 mg, 50%) as apale-yellow gum. ¹H NMR (400 MHz, CDCl₃) δ 8.68 (d, J = 8.0 Hz, 1H), 8.47 (s, 1H), 7.79 (dd, J = 8.3, 1.2 Hz, 1H), 7.36 (d, J = 3.8 Hz, 2H), 7.29 (dd, J = 8.2, 3.9 Hz, 1H), 7.23 – 7.17 (m, 1H), 7.09 (t, J = 7.6 Hz, 2H), 6.81 (dd, J = 7.9, 1.4 Hz, 2H), 6.66 (s, 1H), 4.51 (s, 1H), 3.90 (tdt, J = 11.3, 7.8, 3.9 Hz, 1H), 3.63 – 3.51 (m, 2H), 3.29 (s, 3H), 3.02 (ddd, J = 12.5, 8.7, 5.0 Hz, 1H), 2.62 (dt, J = 12.5, 4.7 Hz, 1H), 2.14 (s, 3H), 2.10 – 1.98 (m, 2H), 1.84 – 1.57 (m, 2H), 1.53 – 1.35 (m, 2H), 1.28 – 1.13 (m, 4H). ¹³C NMR (101 MHz, CDCl₃) δ 164.9, 157.8, 145.04, 135.7, 134.7, 131.7, 129.3, 129.3, 128.9, 127.9, 127.8, 127.0, 126.1, 126.0, 124.0, 119.1, 64.9, 49.2, 48.4, 46.3, 42.0, 37.4, 33.6, 25.8, 25.2, 25.1. Calculated for HRMS (ESI): C₂₉H₃₄N4O (M++H): 455.28054; Found: 455.28019.

(E)-N-cyclohexyl-2-((1,4-dimethyl-3-phenylpiperazin-2-ylidene)amino)-5-iodobenzamide 13t.

Obtained using benzaldehyde and 2-azido-5-iodobenzoic acid following general procedure. Purified by normal-phase chromatography (0–15% EtOAc/CH₂Cl₂) to yield benzamidine 13t (144mg, 88%) as pale yellow oil. Recrystallized from acetonitrile to form clear colorless crystal (See ESI for Crystallographic Experimental Section). m.p.: 85–87°C. ¹H NMR (400 MHz, CDCl₃) δ 8.27 (d, J = 7.9 Hz, 1H), 8.15 (d, J = 2.2 Hz, 1H), 7.32 (dd, J = 8.3, 2.3 Hz, 1H), 7.24 – 7.18 (m, 1H), 7.14 (d, J = 7.6 Hz, 2H), 7.13 (d, J = 8.6 Hz, 0H), 6.85 (d, J = 6.9 Hz, 1H), 6.12 (d, J = 8.3 Hz, 1H), 4.33 (s, 1H), 3.80 (dtd, J = 10.9, 7.3, 3.9 Hz, 1H), 3.64 – 3.42 (m, 2H), 3.22 (s, 3H), 2.98 (ddd, J = 12.7, 7.6, 5.2 Hz, 1H), 2.59 (dt, J = 12.5, 5.0 Hz, 1H), 2.15 (s, 3H), 2.04 – 1.88 (m, 2H), 1.80 – 1.61 (m, 2H), 1.48 – 1.32 (m, 2H), 1.15 (dtdd, J = 23.1, 11.8, 7.9, 3.5 Hz, 2H). ¹³C NMR (101 MHz, CDCl₃) δ 163.7, 157.7, 147.9, 139.3, 139.0, 135.4, 129.2, 128.0, 128.0, 127.4, 125.2, 84.9, 65.5, 49.2, 48.3, 46.8, 42.1, 37.3, 33.5, 33.5, 25.8, 25.1, 25.1. Calculated for HRMS (ESI): C₂₁H₃₅IN4O (M++H): 531.16154; Found: 531.16069.

(E)-3-((1-benzyl-3,4-dicyclopropylpiperazin-2-ylidene)amino)-N-(2-morpholinoethyl) thiophene-2-carboxamide 13x.

Obtained using tert-Butyl benzyl(2-cyclopropylamino)ethyl) carbamate, cyclopropanecarboxaldehyde, 3-azidothiophene-2-carboxylic acid, and 2-morphalinoethyl isocyanide following general procedure. Purified by normal-phase chromatography (0–3% MeOH/CH₂Cl₂) to yield the thiophene carboxamidine, 13x (54 mg, 40%) as a pale-yellow gum. (54 mg, 40%). ¹H NMR (400 MHz, CDCl₃) δ 7.70 (t, J = 5.9 Hz, 1H), 7.43 – 7.24 (m, 7H), 6.49 (d, J = 5.2 Hz, 1H), 5.29 (d, J = 15.3 Hz, 1H), 4.40 (d, J = 15.3 Hz, 1H), 3.64 – 3.47 (m, 6H), 3.32 (ddd, J = 24.2, 11.5, 7.1 Hz, 3H), 3.19 (dq, J = 13.0, 6.4 Hz, 1H), 2.97 (q, J = 6.2, 5.1 Hz, 1H), 2.39 – 2.16 (m, 7H), 1.11 (dp, J = 12.5, 4.3, 3.7 Hz, 1H), 0.62 – 0.26 (m, 5H), 0.16 (dq, J = 10.0, 5.1 Hz, 1H), −0.30 (dq, J = 10.2, 5.1 Hz, 1H). ¹³C NMR (101 MHz, CDCl₃) δ 163.3, 162.3, 149.1, 137.5, 129.0, 127.8, 127.5, 127.1, 124.0, 122.9, 66.9, 62.2, 58.0, 53.5, 51.6, 45.2, 43.6, 36.1, 34.2, 12.3, 7.9, 6.7, 3.9, 3.8. HRMS (ESI): Calculated for C₂₈H₃₇N₅O₂ (M++H): 508.274073; Found: 508.27490.

Modified Procedure for the Telescoped Synthesis of C3-Unsubstituted (E)-Arylamidines

An oven-dried, 10 mL round bottom flask under nitrogen was charged with activated, powdered 4 Ǻ molecular sieves (150 mg). The flask was placed under vacuum and flame-dried, then backfilled with nitrogen, N,N′-Dimethylethylenediamine (115 mg, 0.61 mmol, 2.0 equiv.) was dissolved in dry CH₂Cl₂ (0.9 mL, 0.7 M) and added to the reaction vessel. Formalin, 37 wt. % in H₂0 (0.1 mL, 1.2 mmol, 4.0 equiv.) was measured with syringe added dropwise over a minute to the reaction vessel while stirring at rt. Remainder of the procedure follows general procedure.

(E)-N-cyclohexyl-2-((1,4-dimethylpiperazin-2-ylidene)amino)benzamide 13c.

Obtained using 2-azidobenzoic acid and cyclohexyl isocyanide following modified procedure. Purified by normal-phase chromatography (0–10% MeOH/CH₂Cl₂) to yield the benzamidine, 13c (48 mg, 48%) as an amber gum. ¹H NMR (500 MHz, CDCl₃) δ 8.42 (d, J = 8.0 Hz, 1H), 8.12 (dd, J = 7.9, 1.7 Hz, 1H), 7.29 – 7.25 (m, 1H), 7.09 – 7.04 (m, 1H), 6.65 (d, J = 7.8 Hz, 1H), 3.94 (tdt, J = 11.0, 7.8, 3.8 Hz, 1H), 3.37 (t, J = 5.5 Hz, 2H), 3.12 (s, 3H), 2.95 (s, 2H), 2.61 (t, J = 5.6 Hz, 2H), 2.19 (s, 3H), 1.99 (dq, J = 12.4, 4.0 Hz, 2H), 1.71 (dp, J = 11.9, 3.9 Hz, 2H), 1.63 (dt, J = 12.2, 3.9 Hz, 1H), 1.40 (tdd, J = 15.5, 12.0, 3.6 Hz, 2H), 1.15 (td, J = 12.4, 9.1 Hz, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 166.0, 155.5, 148.3, 131.3, 131.2, 126.0, 123.2, 122.7, 55.1, 52.4, 49.7, 48.4, 45.5, 36.5, 33.6, 25.9, 25.1. HRMS (ESI): Calculated for C₁₉H₂₈N₄O (M++H): 329.23359; Found: 329.23434.

(E)-5-fluoro-N-isopropyl-2-((2-methylhexahydropyrrolo[1,2-a]pyrazin-4(1H)-ylidene)amino) benzamide 13u.

Obtained using tert-butyl 2-((methylamino)methyl)pyrrolidine-1-carboxylate, 2-azido-5-fluorobenzoic acid, and isopropyl isocyanide following modified procedure. Purified by normal-phase chromatography (0–3% EtOAc/CH₂Cl₂) to yield the benzamidine, 13u (51 mg, 50%) as a pale-yellow gum. ¹H NMR (400 MHz, CDCl₃) δ 8.62 (d, J = 7.7 Hz, 1H), 7.85 (dd, J = 10.0, 3.1 Hz, 1H), 7.07 – 6.94 (m, 1H), 6.69 (dd, J = 8.7, 5.0 Hz, 1H), 4.31 – 4.15 (m, 1H), 3.78 – 3.51 (m, 3H), 3.30 (d, J = 16.3 Hz, 1H), 3.08 (dd, J = 10.8, 3.8 Hz, 1H), 2.56 (d, J = 16.2 Hz, 1H), 2.24 (s, 3H), 2.09 (dq, J = 11.8, 6.2, 5.7 Hz, 2H), 1.95 (dd, J = 12.7, 8.7 Hz, 2H), 1.48 (qd, J = 11.7, 7.9 Hz, 1H), 1.19 (dd, J = 6.5, 1.6 Hz, 6H). 19F NMR (376 MHz, CDCl₃) δ −121.28. ¹³C NMR (101 MHz, CDCl₃) δ 170.2, 164.7, 164.7, 159.9, 157.5, 154.5, 144.7, 144.7, 144.6, 127.2, 127.1, 124.7, 124.6, 118.3, 118.1, 117.2, 116.9, 57.9, 57.8, 54.2, 45.8, 45.2, 41.3, 30.4, 23.1, 23.0, 22.5. HRMS (ESI): Calculated for C₁₈H₂₅FN₄O (M++H): 333.20852; Found: 333.20814.

(E)-3-((1,4-dimethylpiperazin-2-ylidene)amino)-N-(4-methoxyphenyl)thiophene-2-carboxamide 13v.

Obtained using 3-azidothiophene-2-carboxylic acid and 4-methoxyphenyl isocyanide following modified procedure. Purified by normal-phase chromatography (0–3% MeOH/EtOAc) to yield the thiophene carboxamidine, 13v (32mg, 29%) as a light-brown solid. m.p.: 125–127°C. ¹H NMR (400 MHz, CDCl₃) δ 10.21 (s, 1H), 7.55 – 7.46 (m, 2H), 7.35 (d, J = 5.2 Hz, 1H), 6.89 – 6.83 (m, 2H), 6.60 (d, J = 5.2 Hz, 1H), 3.80 (s, 3H), 3.43 (t, J = 5.6 Hz, 2H), 3.22 (s, 4H), 2.67 (t, J = 5.6 Hz, 2H), 2.30 (s, 3H). ¹³C NMR (101 MHz, CDCl₃) δ 160.9, 157.1, 155.7, 147.9, 132.1, 128.1, 124.5, 123.8, 121.2, 114.2, 55.5, 55.4, 52.0, 49.7, 45.5, 36.7. HRMS (ESI): Calculated for C₁₈H₂₂N₄O₂S (M++H): 359.15362; Found: 359.15459.

(E)-3-((1,4-dimethylpiperazin-2-ylidene)amino)-N-(4-methoxyphenyl)furan-2-carboxamide 13w.

Obtained using 3-azidofuran-2-carboxylic acid and 4-methoxyphenyl isocyanide following modified procedure. Purified by normal-phase chromatography (5–30% EtOAc/CH₂Cl₂) to yield furan carboxamidine, 13w (21 mg, 20%) as a light-brown solid. m.p.: 150–151°C. ¹H NMR (400 MHz, CDCl₃) δ 9.82 (s, 1H), 7.51 (d, J = 9.0 Hz, 2H), 7.44 (d, J = 1.9 Hz, 1H), 6.87 (d, J = 9.1 Hz, 2H), 6.17 (d, J = 1.9 Hz, 1H), 3.79 (s, 3H), 3.43 (t, J = 5.6 Hz, 2H), 3.31 (s, 2H), 3.20 (s, 3H), 2.69 (t, J = 5.6 Hz, 2H), 2.35 (s, 3H). ¹³C NMR (101 MHz, CDCl₃) δ 157.7, 157.5, 155.7, 143.8, 137.5, 136.7, 132.0, 121.2, 114.2, 108.9, 55.5, 55.4, 51.9, 49.7, 45.5, 36.9. HRMS (ESI): Calculated for C₁₈H₂₂N₄O₃ (M++H): 343.17647; Found: 343.17700.