Bifunctional building blocks in the Ugi-azide condensation reaction: A general strategy toward exploration of new molecular diversity

Abstract

1,5-disubstituted tetrazoles are an important drug-like scaffold known for their ability to mimic the cis-amide bond conformation. The scaffold is readily accessible via substitution of the carboxylic acid component of the Ugi multi-component reaction (MCR) with TMSN₃ in what is herein denoted the Ugi-azide reaction. This full paper presents a concise, novel, general strategy to access a plethora of new heterocylic scaffolds utilizing tethered aldo/keto-acids/esters in the Ugi-azide reaction followed by a ring closing event that generates novel highly complex bis-heterocyclic lactam-tetrazoles.

Introduction

The design of peptidomimetics to circumvent small molecule biological stability issues, thus delivering improved pharmacokinetic profiles, has gained massive interest over the last twenty years.¹ In particular, cis-amide bonds have been shown to play key roles in protein secondary structures involved in several important biological systems.² In studies to determine effective mimics of the cis-amide bond, the tetrazole ring and more specifically the 1,5-disubstituted tetrazole, has proven to be a valuable bioisostere, extensively reported on by Marshall et al.³ The biological significance of related ring systems has grown in recent years with a number of tetrazole analogs reported to exhibit biological activity toward the cannabinoid-1 receptor (CB1),⁴ fatty acid amide hydrolase,⁵ melanin-concentrating hormone receptor 1,⁶ polo-like kinase 1,⁷ and to act as orally effective human growth hormone secretagogues.⁸ Clearly, development of concise routes to novel 1,5-disubstituted tetrazole chemical space has the potential to deliver small molecule partners or probes for new or established protein receptors, enabling studies on protein function or even initiation of translational campaigns.

The classical Ugi MCR is comprised of four components, an aldehyde, amine, isocyanide and carboxylic acid, which on mixing generate the peptidic-like structure A containing 4 points of diversification (Scheme 1). As such, it is probably the premiere isocyanide based MCR, and subsequent chemical manipulation of the flexible product has received immense interest in the medicinal chemistry community providing access to arrays of highly diverse small molecules.⁹ Moreover, an offspring of the Ugi reaction, denoted the Ugi-azide reaction, offers a concise chemical route to 1,5-disubstituted tetrazoles which is initiated with simple replacement of the carboxylic acid with TMSN₃, delivering 1,5-disubstituted tetrazoles B (Scheme 1).¹⁰ Through use of a variety of assorted reagents and systematically exploring different ring closing possibilities of the Ugi-azide product B, unique scaffolds such as ketopiperazine-tetrazoles,¹¹ azepine-tetrazoles,¹² benzodiazepine-tetrazoles¹³ and quinoxaline-tetrazoles¹⁴ have been successfully generated.

Scheme 1.

Ugi and Ugi-azide MCR

Recently, we reported on the use of methyl levulinate 1, a tethered keto-ester, in the Ugi-azide MCR followed by subsequent rigidification.¹⁵ This full paper details the versatility and generality of the methodology with greatly enhanced scope in tether diversity between the aldehyde and electrophilic acid or ester appendage (Scheme 2), enabling access to multiple collections of bis-heterocyclic lactam-tetrazoles recently submitted to the United States Molecular Libraries Small Molecule Repository (MLSMR).

Scheme 2.

General strategy to lactam-tetrazoles

Results and discussion

Syntheses of tetrazolyl-pyrrolidinones and -indolinones

Initial studies concentrated on exploring the suitability of commercially available methyl levulinate 1 to provide the tetrazolyl-lactam 5a with supporting reagents thiophen-2-ylamine 2 and 2-isocyano-1,3-dimethylbenzene 3 (Scheme 3).¹⁵ After formation of the Ugi product 4, direct addition of a solution of 10% TFA in DCE [Note: without removal of MeOH] facilitated lactam formation to give 5a in 56% yield over two steps (Scheme 3). Interestingly, when methanol was removed prior to addition and dissolution of 4 in 10% TFA/DCE, 5a was only observed in negligible amounts. The Ugi product was thus isolated and subjected to basic conditions (Scheme 3, Scheme 2. KOH, MeOH, THF, H₂O). Gratifyingly, 2a was attained in comparable yields (59% over 2 steps), presumably through cyclization of the secondary amine directly onto a newly formed carboxylic acid from the methyl ester moiety. With two complementary routes in hand the more operationally friendly acid mediated protocol was employed to establish the reactivity domain through preparation of a further eight tetrazolyl-pyrrolidinones 2 (Table 1). Furthermore, the methodology was importantly shown to be compatible with plate based production, delivering 96 congeners in rapid fashion.¹

Scheme 3.

Access to tetrazolyl-pyrrolidinone 5a

Table 1.

Tetrazolyl-pyrrolidinones series

R1	R2	Product	Yield (%)
		5b	78
		5c	54
		5d	69
		5e	59
		5f	52
		5g	64
		5h	40
		5i	48

Encouraged by this operationally friendly protocol, we embarked upon additional studies of new tether diversity exploring the production of tetrazolyl-indolinones 10. Preliminary attempts focused on the use of methyl 2-acetylbenzoate 8a, n-pentyl isocyanide 7a and furfurylamine 6a in the Ugi-azide MCR (Scheme 4). Unexpectedly, the condensation performed poorly for the acetophenone 8a, whereas the aldehyde congener, methyl 2-formylbenzoate 8b, performed in exemplary fashion and 10b was formed directly without the need for addition of acid (85% isolated yield, 2 steps).

Scheme 4.

Synthesis of 2-(furan-2-ylmethyl)-isoindolin-1-one 10b

Eight analogs were thus prepared using an assortment of primary amines and isocyanides (Table 2) and the chemistry was progressed to plate based production delivering 96 additional analogs of indolinone-tetrazoles 8.¹⁸

Table 2.

Indolinone tetrazole series

R1	R2	Product	Yield (%)
		10c	51
		10d	58
		10e	66
		10f	43
		10g	51
		10h	58
		10i	29
		10j	36

Syntheses of tetrazolyl-piperidinones, -ketopiperazines, and-thiomorpholinones

Using the same diversity reagents 6a and 7a, the feasibility of expanding the generality of this methodology to afford 6 membered rings was subsequently investigated with bifunctional reagents methyl ester 11a and free carboxylic acid 11b. Thus, after Ugi-azide reaction of 6a, 7a and 11a, TFA was added to the methanolic reaction medium of 12a and contrary to observations with its 5-membered ring congener no cyclization to desired product 13a was observed.

From prior experience with 4 (Scheme 3) possessing both ester and amine functionalities akin to 12a, lactamization was attempted via two additional steps i.e. ester cleavage to the free acid and amide bond formation to afford the lactam. Thus, reaction of methyl 5-oxohexanoate 11a in the azide modified Ugi reaction with 6a and 7a (Scheme 5) gave the Ugi amino-ester 12a (83% yield). Basic hydrolysis of 12a and subsequent 1-ethyl-3-(3-dimethyllaminopropyl)-carbodiimide (EDC) or SOCl₂ mediated intramolecular amide coupling provided 13 in 75% and 83% yield respectively over the final two steps. Looking to improve the route to 13, we investigated utilizing the tethered keto-acid 11b in the Ugi-Azide MCR and, to our delight, the Ugi product 12b as opposed to 18 was formed, Scheme 6. Without purification of 12b, coupling agent 1,1’-carbonyldiimidazole (CDI) was able to catalyze lactam formation to provide tetrazolyl-piperidinone 13b in 37% overall yield for the combined two steps (Scheme 5). With a general one-pot, two-step optimized procedure in hand, five other examples were prepared using an assortment of primary amines and isocyanides reported previously.¹⁶ Mechanistically, this was intriguing and a postulated sequence of events is depicted in Scheme 6.¹⁹ Thus, condensation of an aldo-acid and a primary amine forms imine 15. Upon imine protonation, isocyanide addition forms the intermediate nitrilium ion 16. The classical intramolecular Ugi MCR (Path a) would typically afford lactam 18 after Mumm rearrangement. However, the small and highly nucleophilic azide ion intercepts 16 (Path b) in preference to intramolecular ring closure with the free carboxylic acid, affording 17 which is ready for CDI mediated ring closure. Further efforts were devoted to enrich molecular diversity through the assembly of more elaborated heterocyclic cores and three additional libraries incorporating unique molecular features and six membered rings found in medicinally valuable compounds were thus evaluated for route feasibility. Thus, integration of a sulphur atom into the 6-membered ring to generate thiomorpholinone derivatives 20 was attempted. This peculiar moiety has been the subject of intense study due to its pharmacological properties depicted as a 1,4-benzothiazine framework in the calcium antagonist Semotiadil.²⁰ When keto-acid 19a (R = H) was mixed with 2,5-dimethoxybenzylamine and cyclopentyl isocyanide, competition between path a and b, illustrated in Scheme 6 gave two products, i.e. 17 and 18 derivatives. Subsequently, the crude mixture was treated with CDI to give 20a in only 21% yield. Due to this low yield, we turned our attention to methyl 2-((2-oxopropyl)thio)acetate 19b (R = Me), prepared from methyl thioglycolate and chloroacetone, which delivered 20a in 69% yield in two steps. Accordingly, a variety of primary amines, isocyanides and 19b were evaluated to establish a preliminary reactivity domain and furnish an array of five unique thiomorpholinones 20a-e (Table 3).

Scheme 5.

Optimization of the preparation of piperidine-tetrazole 13

Scheme 6.

Ugi-azide condensation to afford 17

Table 3.

Array of thiomorpholinone-tetrazole derivatives 20

R1	R2	Product	Ugi (%)	Final Steps* (%)
		20a	78	88
		20b	61	66
		20c	42	22
		20d	86	73
		20e	61	96

^*Basic hydrolysis and SOCl₂ activation

Another enticing moiety that drew our attention was the 4-sulfonyl-2-piperazinone skeleton embedded in 22. This conformationally restricted motif represents an essential structural feature of human factor Xa and gene transcription inhibitors.^21,22 Indeed, sulfonamide keto-acids have previously been reported as highly compatible bifunctional reagents in intramolecular Ugi three component condensations affording 5-carbamoyl-5-methyl-4-sulfonyl-2-piperazinones in a single step.²³ The sulfonamide keto-ester 21 was thus synthesized from glycine methyl ester in two steps consisting of sequential sulfonylation and alkylation using 18-crown-6 as a phase-transfer catalyst and a relatively mild base (K₂CO₃). A series of six 4-sulfonyl-2-piperazinones 22 were generated to confirm the utility of 21 in producing novel tetrazolo-fused analogs, thereby further expanding the generality of the lactam-tetrazole forming methodology depicted in Scheme 2 (Table 4).

Table 4.

Array of 4-sulfonyl-2-piperazinone-tetrrazole derivatives

R1	R2	Product	Ugi (%)	Final Steps* (%)
		22a	16	78
		22b	27	93
		22c	59	82
		22d	55	86
		22e	74	58
		22f	64	64

^*Basic hydrolysis and SOCl₂ activation

Additional attempts to further diversify the portfolio of scaffolds derived from this methodology were carried out by fusing heteroaromatic rings onto the bifunctional input. In particular, derivatives of 4,5,6,7-tetrahydropyrazolo[1,5-a]-pyrazine-4-one represent an uncultivated set of pharmaceutically relevant compounds where the scaffold is currently found in both fibrinogen and vitronectin receptor antagonists.^24,25 Intrigued by the potential new biological applications of this rare bifunctional substituted-pyrazole methyl ester²⁶, it was thus employed with supporting reagents 6 and 7 in the development of new synthetic route to scaffold 24. Alkylation of methyl 1H-pyrazole-3-carboxylate with chloroace- tone under phase transfer conditions in the presence of K₂CO₃ and 18-crown-6 provided 23 in a single step. In analogous fashion to prior methods reported herein, 23 was mixed with a variety of primary amines and isocyanides in the Ugi-Azide MCR. Subsequent basic hydrolysis and SOCl₂-mediated ring closure furnished a compilation of five 4,5,6,7-tetrahydropyrazolo[1,5-a]-pyrazine-4-one derivatives 24a-e depicted in Table 5 with moderate to good isolated yields.

Table 5.

Array of 4,5,6,7-tetrahydropyrazolo[1,5-a]-pyrazine-4-one tetrazole derivatives 24

R1	R2	Product	Ugi (%)	Final Steps* (%)
		24a	74	51
		24b	73	57
		24c	67	78
		24d	51	72
		24e	42	55

^*Basic hydrolysis and SOCl₂ activation

Syntheses of tetrazolyl-azepanones, -thiazepanones, and -benzoxazepinones

With five diverse scaffolds in hand, we subsequently expanded the generality to variations of seven-membered ring lactams. Initial efforts were devoted to preparations of 1-(furan-2-ylmethyl)-7-methyl-7-(1-pentyl-1H-tetrazol-5-yl)azepan-2-one 27 analogs (Scheme 7). In similar fashion with attempts to prepare tetrazolyl-piperidines 13, TFA failed to deliver 27 after direct addition of TFA/DCE to a methanolic solution of the on-going Ugi-azide reaction with 25a (R=Me) and supporting reagents 6a and 7a. However, unlike 13 which was accessible via CDI or EDC-mediated amide coupling, 27 was not obtained after similar coupling methods were employed with crude 26b (R=H). Azepine-tetrazole 27 was ultimately generated in 48% yield through SOCl₂ triggered in situ acyl chloride formation on partially purified 26b (Scheme 7). Due to its high polarity, complete isolation of 26b did prove difficult and hence attention was turned to the Ugi amino-ester 26a, synthesized from methyl 6-oxoheptanoate 25a (82% yield). Yield improvement to 62% was observed when 27 was produced from 26a (R=H) in two steps comprising consecutive basic hydrolysis and in situ acyl chloride formation (Scheme 7). This method was exemplified by the assembly of four analogs and has been previously reported.¹⁶

Scheme 7.

Optimization of azepinone-tetrazoles 27

Thiazepanone derivatives 29 were successfully prepared in similar fashion to the thiomorpholinones 20. The key reagent in production of this derivative, namely methyl 2-((3-oxobutyl)thio)acetate 28, was prepared from methyl thioglycolate and 4-chlorobutan-2-one in one step. Upon completion of the Ugi-azide condensation, MCR intermediates were subjected to the optimized two-step protocol to ultimately afford five examples 29a-e in good overall yields for the 3 step process (Table 6).

Table 6.

Array of [1,4]thiazepanone derivatives 29

R1	R2	Product	Ugi (%)	Final Steps* (%)
		29a	68	57
		29b	70	66
		29c	70	54
		29d	61	45
		29e	75	51

^*Basic hydrolysis and SOCl₂ activation

A final example highlighting the generality of this methodology enabled access to the tetrazolo-benzoxazepinones 31. Akin to the [1,4]thiazepanone 29, the benzo[1,4]oxazepinone fragment may also be viewed as a relatively under-developed scaffold in the pharmaceutical sector, although, a handful of articles do describe some utility with the chemotype observed embedded in ACE/neutral endopeptidase (NEP)²⁷ and HIV-1²⁸ inhibitors. Methyl esterification of 2-(2-formylphenoxy)acetic acid generated methyl 2-(2-formylphenoxy)acetate 30, that was used as the tethered bifunctional component (Table 7). Six analogs 31a-31f were synthesized and the structure of 31c was confirmed by X-ray crystallography (Figure 1).²⁹

Table 7.

Array of benzo[1,4]oxazepinone derivatives 31

R1	R2	Product	Ugi e(%)	Final Steps* (%)
		31a	80	29
		31b	63	31
		31c	74	84
		31d	78	70
		31e	77	35
		31f	66	62

^*Basic hydrolysis and SOCl₂ activation

Figure 1.

X-Ray crystal structure of 31c

Conclusions

A straightforward, robust and extremely versatile strategy coupling the Ugi-Azide MCR with amidative post-condensation modifications enabling ring-closure to a variety of pharmacologically relevant scaffolds has been established. In this context, tethered aldo-esters/keto-acids/keto-esters were key bifunctional precursors that in combination with supporting isonitrile and amine reagents typically afforded the Ugi-azide adduct in good yield. Not surprisingly during the optimization of the post-condensation ring closing methodology, it was apparent that stronger activating reagents were required as the desired lactam ring size increased, yet all of the 5 to 7-exo-trig processes remained, as expected, ultimately feasible.³⁰ By means of this general route, nine bis-heterocyclic tetrazolo-scaffolds and related congener sets were prepared incorporating a wide array of bifunctional input linker diversity (Scheme 2, x = linker) and additional diversity elements from supporting reagents 6 and 7. Coupled with the cis-amide bond surrogacy possessed by the 1,5-disubstituted tetrazole nucleus, these new bis-heterocylic scaffolds represent potential innovative new molecular probes to interrogate peptidergic biological systems.

Experimental

General remarks

All reagents were purchased from Acros Organics, Alfa Aesar, Sigma Aldrich and TCI America. Microwave assisted reactions were conducted in a 10-ml vial on a CEM microwave initiator. The flash column chromatography was carried out on Teledyne Isco CombiFlash Rf 200. ¹H and ¹³C NMR spectra were recorded in CDCl₃ or DMSO_d6 on a Varian 400 MHz spectrometer. Chemical shifts in ¹H NMR spectra are reported in parts per million (ppm, d) downfield from the internal standard Me₄Si (TMS). Chemical shifts in ¹³C NMR spectra are reported relative to the central line of the chloroform signal (d = 77.70 ppm) or the DMSO signal (d = 40.0 ppm). Low-resolution mass spectra were obtained with a Shimadzu Prominence UFLCXR/LCMS-2020/ELSD-LTII instrument. High-resolution mass spectra were obtained with 9.4 Tesla Bruker FT/ICR-MS instrument.

General procedure for aldo/keto-esters (8b, 19b, 28 and 30)

All can be found in the electronic supplementary information.

General experimental procedure for synthesis of indolinone tetrazoles (10b-10j)

Methyl 2-formylbenzoate 8b (0.250 mmol), R₁NH₂ 6 (0.250 mmol), TMSN₃ (0.250 mmol) and R₂NC 7 (0.250 mmol) were dissolved in MeOH (1.0 ml) in a 10 ml vial. The reaction was allowed to run at room temperature for 24 h. The crude mixture was concentrated in vacuo and purified by flash chromatography (Hexane/EtOAc) to afford the indolinone tetrazoles.

2-(furan-2-ylmethyl)-3-(1-pentyl-1H-tetrazol-5-yl)isoindo-lin-1-one (10b)

white solid (m.p. 95–97 °C); 85% yield (one step); ¹H NMR (400 MHz, CDCl₃) δ ppm 8.02 – 7.97 (m, 1H), 7.65 – 7.56 (m, 2H), 7.28 – 7.22 (m, 2H), 6.26 – 6.21 (m, 2H), 6.19 – 6.15 (m, 1H), 4.78 (d, J = 15.6 Hz, 1H), 4.57 (d, J = 15.6 Hz, 1H), 3.57 (ddd, J = 14.8, 8.8, 6.3 Hz, 1H), 3.43 (ddd, J = 14.8, 8.8, 6.3 Hz, 1H), 1.38 – 1.24 (m, 1H), 1.19 – 1.08 (m, 1H), 1.08 – 0.95 (m, 2H), 0.89 – 0.78 (m, 2H), 0.71 (t, J = 7.3 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 167.7, 150.2, 148.6, 142.9, 140.3, 133.0, 131.2, 130.1, 124.7, 123.1, 110.7, 109.6, 55.1, 55.0, 47.6, 38.1, 28.4, 28.2, 21.7, 13.6; [M+H]⁺ = 352.4; HRMS (ESI): m/z calcd for (C₁₉H₂₂N₅O₂): 352.1768; found: 352.1772.

3-(1-cyclopentyl-1H-tetrazol-5-yl)-2-(2,5-dimethoxybenzyl) isoindolin-1-one (10c)

yellow solid (m.p. 118–119 °C); 51% yield (one step); ¹H NMR (400 MHz, CDCl₃) δ ppm 8.01 – 7.94 (m, 1H), 7.62 – 7.50 (m, 2H), 7.21 – 7.15 (m, 1H), 6.96 – 6.91 (m, 1H), 6.77 (ddd, J = 8.9, 3.0, 1.6 Hz, 2H), 6.71 (dd, J = 8.9, 1.3 Hz, 2H), 6.20 (s, 1H), 4.96 (d, J = 14.5 Hz, 1H), 4.41 (d, J = 14.4 Hz, 1H), 3.99 – 3.88 (m, 1H), 3.74 (s, 3H), 3.68 (s, 3H), 2.01 – 1.75 (m, 3H), 1.74 – 1.59 (m, 1H), 1.59 – 1.47 (m, 1H), 1.41 – 1.28 (m, 1H), 1.19 – 1.07 (m, 1H), 1.06 – 0.92 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 168.4, 153.5, 151.4, 150.3, 140.8, 132.8, 131.3, 129.8, 124.4, 124.3, 123.1, 116.7, 114.4, 111.3, 59.3, 55.74, 55.68, 55.4, 39.9, 33.4, 32.6, 24.7, 24.6; [M+H]⁺ = 420.3; HRMS (ESI): m/z calcd for (C₂₃H₂₆N₅O₃): 420.20302; found: 420.20308.

3-(1-benzyl-1H-tetrazol-5-yl)-2-(thiophen-2-ylmethyl)iso-indolin-1-one (10d)

yellow solid (m.p. 134–136 °C); 58% yield (one step); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.95 (d, J = 7.6 Hz, 1H), 7.53 (t, J = 7.6 Hz, 1H), 7.38 (td, J = 7.6, 1.3 Hz, 1H), 7.24 – 7.18 (m, 2H), 7.16 (td, J = 7.3, 1.4 Hz, 2H), 6.97 – 6.93 (m, 1H), 6.90 (ddd, J = 5.1, 3.5, 1.7 Hz, 1H), 6.83 – 6.79 (m, 1H), 6.68 (d, J = 7.9 Hz, 2H), 6.15 (s, 1H), 4.89 (dd, J = 15.4, 4.5 Hz, 2H), 4.62 (d, J = 15.3 Hz, 1H), 4.12 (d, J = 15.5 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 167.5, 150.4, 139.7, 137.3, 132.9, 132.3, 131.2, 130.0, 128.8, 128.7, 127.8, 127.2, 127.1, 126.5, 124.6, 123.1, 54.0, 51.2, 39.3; [M+H]⁺ = 388.3; HRMS (ESI): m/z calcd for (C₂₁H₁₈N₅OS): 388.12266; found: 388.12239.

2-(2,5-dimethoxybenzyl)-3-(1-(2,6-dimethylphenyl)-1H-tetrazol-5-yl)isoindolin-1-one (10e)

white solid (m.p. 167–169 °C); 66% yield (one step); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.61 – 7.57 (m, 1H), 7.46 – 7.41 (m, 1H), 7.41 – 7.36 (m, 1H), 7.30 – 7.26 (m, 2H), 7.19 – 7.12 (m, 2H), 6.80 – 6.73 (m, 4H), 6.09 (s, 1H), 4.95 (d, J = 15.0 Hz, 1H), 4.10 (d, J = 15.0 Hz, 1H), 3.78 (s, 3H), 3.69 (s, 3H), 2.04 (s, 3H), 1.22 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 167.6, 153.6, 152.4, 151.5, 139.7, 135.3, 135.0, 131.7, 131.5, 131.2, 130.7, 129.5, 128.7, 128.3, 124.8, 123.9, 123.2, 116.1, 113.8, 111.4, 55.8, 55.7, 54.4, 39.8, 17.6, 17.0; [M+H]⁺ = 456.3; HRMS (ESI): m/z calcd for (C₂₆H₂₆N₅O₃): 456.20302; found: 456.20242.

2-(2-(1H-indol-3-yl)ethyl)-3-(1-(tert-butyl)-1H-tetrazol-5-yl)isoindolin-1-one (10f)

white solid (m.p. 108–110 °C); 43% yield (one step); ¹H NMR (400 MHz, DMSO_d6) δ ppm 10.83 (s, 1H), 7.88 – 7.80 (m, 1H), 7.63 – 7.56 (m, 2H), 7.37 – 7.27 (m, 3H), 7.11 (s, 1H), 7.04 (t, J = 7.5 Hz, 1H), 6.92 (t, J = 7.2 Hz, 1H), 6.68 (s, 1H), 3.94 – 3.83 (m, 1H), 3.15 – 2.93 (m, 2H), 2.82 – 2.71 (m, 1H), 1.81 (s, 9H); ¹³C NMR (100 MHz, DMSO_d6) δ ppm 167.71, 153.00, 143.32, 136.63, 132.83, 131.69, 129.76, 127.31, 123.80, 123.29, 123.25, 121.51, 118.80, 118.22, 111.94, 111.26, 62.67, 55.24, 42.53, 40.60, 40.39, 40.18, 39.97, 39.76, 39.56, 39.35, 30.27, 24.28; [M+H]⁺ = 401.4; HRMS (ESI): m/z calcd for (C₂₃H₂₅N₆O): 401.20844; found: 401.20824.

3-(1-cyclohexyl-1H-tetrazol-5-yl)-2-(4-hydroxyphenethyl) isoindolin-1-one (10g)

white solid (m.p. 162–164 °C); 51% yield (one step); ¹H NMR (400 MHz, CDCl₃) δ ppm 8.04 – 7.94 (m, 1H), 7.66 – 7.55 (m, 2H), 7.26 – 7.22 (m, 1H), 7.06 – 7.00 (m, 2H), 6.84 – 6.75 (m, 2H), 6.52 – 6.40 (m, 1H), 6.09 (s, 1H), 4.22 – 4.11 (m, 1H), 3.13 (tt, J = 11.6, 3.7 Hz, 1H), 3.05 – 2.90 (m, 2H), 2.80 – 2.69 (m, 1H), 2.00 – 1.49 (m, 8H), 1.15 – 1.03 (m, 2H), 0.92 (dd, J = 16.4, 11.1 Hz, 1H), 0.68 – 0.54 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 168.0, 155.1, 149.5, 140.2, 132.9, 131.6, 130.2, 129.7, 128.9, 124.4, 123.0, 115.7, 58.9, 54.9, 42.7, 33.3, 32.7, 32.6, 25.2, 25.1, 24.4; [M+H]⁺ = 404.4; HRMS (ESI): m/z calcd for (C₂₃H₂₆N₅O₂): 404.20810; found: 404.20828.

3-(1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-1H-tetrazol-5-yl)-2-isobutylisoindolin-1-one (10h)

yellow solid (m.p. 66–67 °C); 58% yield (one step); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.70 – 7.64 (m, 1H), 7.58 – 7.45 (m, 2H), 7.29 (d, J = 7.4 Hz, 1H), 6.68 – 6.64 (m, 1H), 6.23 (s, 1H), 6.17 – 6.14 (m, 1H), 4.32 – 4.11 (m, 5H), 3.66 (dd, J = 13.9, 9.5 Hz, 1H), 2.48 (dd, J = 13.9, 5.7 Hz, 1H), 2.09 – 1.96 (m, 1H), 0.94 (d, J = 6.6 Hz, 3H), 0.86 (d, J = 6.7 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 167.6, 151.7, 145.5, 143.5, 140.2, 132.2, 132.0, 129.6, 125.1, 124.0, 122.8, 118.3, 117.6, 114.6, 64.3, 64.1, 54.6, 48.0, 27.5, 20.3, 19.7; [M+H]⁺ = 392.3; HRMS (ESI): m/z calcd for (C₂₁H₂₂N₅O₃): 392.17172; found: 392.17184.

2-(1-benzylpiperidin-4-yl)-3-(1-(4-methoxyphenyl)-1H-tetrazol-5-yl)isoindolin-1-one (10i)

light tangerine solid (m.p. 83–84 °C); 29% yield (one step); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.62 (d, J = 7.4 Hz, 1H), 7.52 (td, J = 7.5, 1.3 Hz, 1H), 7.45 (t, J = 7.4 Hz, 1H), 7.35 – 7.22 (m, 7H), 6.70 – 6.64 (m, 2H), 6.63 – 6.57 (m, 2H), 6.29 (s, 1H), 4.15 – 4.03 (m, 1H), 3.77 (s, 3H), 3.47 (s, 2H), 2.97 – 2.89 (m, 1H), 2.88 – 2.80 (m, 1H), 2.08 – 1.99 (m, 3H), 1.69 (d, J = 9.4 Hz, 1H), 1.72 – 1.64 (m, 1H), 1.48 – 1.39 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 168.2, 160.9, 153.2, 141.1, 138.3, 132.4, 132.1, 129.7, 128.9, 128.2, 127.0, 126.7, 125.3, 124.0, 122.7, 114.3, 62.6, 55.6, 52.8, 52.7, 51.6, 30.1, 29.9; [M+H]⁺ = 481.3; HRMS (ESI): m/z calcd for (C₂₈H₂₉N₆O₂): 481.23465; found: 481.23441.

2-cyclopropyl-3-(1-(naphthalen-2-yl)-1H-tetrazol-5-yl)iso-indolin-1-one (10j)

light tangerine solid (m.p. 88–89 °C); 36% yield (one step); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.85 (d, J = 8.0 Hz, 1H), 7.79 (d, J = 8.7 Hz, 1H), 7.59 – 7.51 (m, 4H), 7.46 (d, J = 7.5 Hz, 1H), 7.40 (d, J = 7.7 Hz, 1H), 7.33 (d, J = 7.6, H), 7.10 (d, J = 2.0 Hz, 1H), 6.96 (dd, J = 8.7, 2.2 Hz, 1H), 6.17 (s, 1H), 2.47 – 2.39 (m, 1H), 0.95 – 0.88 (m, 1H), 0.81 – 0.72 (m, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 168.4, 152.3, 140.4, 133.5, 132.5, 132.2, 129.8, 129.8, 128.3, 128.2, 128.0, 127.7, 124.7, 124.0, 122.8, 121.7, 55.8, 24.2, 6.6, 5.1; [M+H]⁺ = 368.3; HRMS (ESI): m/z calcd for (C₂₂H₁₈N₅O): 368.1506; found: 368.1513.

General experimental procedure for synthesis of tetrazolyl-thiomorpholinones (20a–e), tetrazolyl ketopiperazines (22a–f and 24a–e), tetrazolyl-thiazepanones (29a–e), and tetrazolyl-benzoxazepinones (31a–f)

Bifunctional reagents (20, 22, 24, 29 or 31, 0.250 mmol), R₁NH₂ (0.250 mmol), TMSN₃ (0.250 mmol) and R₂NC (0.250 mmol) were dissolved in MeOH (1.0 ml) in a 10 ml vial. The reaction was allowed to run at room temperature for 24 h. The crude mixture was concentrated in vacuo and purified by flash chromatography (Hexane/EtOAc) to afford the Ugi-tetrazoles. Subsequently, MeOH (1.5 ml), THF (0.75 ml), and H₂O (0.5 ml) were added, followed by 0.03 ml of a 1g/1ml solution of KOH in H₂O and the reaction mixture was irradiated in a microwave initiator at 100 °C for 5 min. Upon acidification with 1 M HCl solution to pH 2, the hydrolyzed product was then extracted with EtOAc (3 × 2 ml) and the organic layer was dried over Na₂SO₄ and concentrated in vacuo. The residue was dissolved in DCE (2 ml) followed by addition of SOCl₂ (1.5 eq) and the reaction was refluxed at 85 °C. When completed, TEA (0.5 ml) was added and the mixture was stirred for 2 h before being purified by flash chromatography (hexane/EtOAc) on silica gel to afford final products.

5-(1-cyclopentyl-1H-tetrazol-5-yl)-4-(2,5-dimethoxybenzyl)-5-methylthiomorpholin-3-one (20a)

viscous liquid; 69% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 6.76 – 6.66 (m, 3H), 4.98 (d, J = 16.5 Hz, 1H), 4.88 – 4.77 (m, 1H), 3.80 – 3.70 (m, 4H), 3.67 (s, 3H), 3.63 (d, J = 17.2 Hz, 1H), 3.53 (d, J = 17.2 Hz, 1H), 3.20 (d, J = 14.4 Hz, 1H), 3.08 (d, J = 14.3 Hz, 1H), 2.31 – 2.20 (m, 1H), 2.20 – 2.02 (m, 5H), 1.98 (s, 3H), 1.83 – 1.66 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 166.5, 155.8, 153.5, 150.2, 125.9, 114.4, 111.5, 110.6, 63.1, 60.6, 55.6, 55.5, 43.6, 40.0, 35.2, 34.4, 32.7, 27.1, 25.2, 25.1; [M+H]⁺ = 418.2; HRMS (ESI): m/z calcd for (C₂₀H₂₈N₅O₃S): 418.19074; found: 418.19068.

5-(1-cyclohexyl-1H-tetrazol-5-yl)-4-(4-hydroxyphenethyl)-5-methylthiomorpholin-3-one (20b)

viscous liquid; 40% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.00 (dd, J = 8.3, 1.6 Hz, 2H), 6.78 (dd, J = 8.3, 1.6 Hz, 2H), 4.51 (tt, J = 11.7, 3.8 Hz, 1H), 4.19 – 4.06 (m, 1H), 3.81 (td, J = 11.9, 4.3 Hz, 1H), 3.55 (d, J = 17.3 Hz, 1H), 3.45 (d, J = 17.3 Hz, 1H), 3.18 – 2.98 (m, 2H), 2.65 (td, J = 12.0, 5.2 Hz, 1H), 2.42 (td, J = 11.8, 5.0 Hz, 1H), 2.27 (d, J = 11.4 Hz, 1H), 2.19 (s, 3H), 2.14 – 1.67 (m, 4H), 1.57 – 1.42 (m, 1H), 1.40 – 1.21 (m, 4H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 165.9, 155.2, 155.0, 140.5, 129.8, 115.6, 62.4, 60.2, 58.9, 49.0, 39.7, 34.0, 33.8, 33.0, 27.3, 25.7, 25.4, 24.8, 24.6; [M+H]⁺ = 402.2; HRMS (ESI): m/z calcd for (C₂₀H₂₈N₅O₂S): 402.1958; found: 402.1957.

4-(3-(1H-imidazol-1-yl)propyl)-5-(1-(2,6-dimethylphenyl)-1H-tetrazol-5-yl)-5-methylthiomorpholin-3-one (20c)

viscous liquid; 9% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.46 – 7.38 (m, 2H), 7.24 (d, J = 7.6 Hz, 2H), 7.03 (s, 1H), 6.87 (s, 1H), 4.08 – 3.96 (m, 1H), 3.96 – 3.83 (m, 1H), 3.55 – 3.44 (m, 1H), 3.37 (d, J = 17.0 Hz, 1H), 3.12 (d, J = 15.7 Hz, 1H), 3.05 (d, J = 15.7 Hz, 1H), 2.85 (d, J = 14.1 Hz, 1H), 2.73 – 2.58 (m, 1H), 2.39 – 2.23 (m, 1H), 1.87 (s, 3H), 1.86 (s, 3H), 1.56 (s, 3H), 1.26 (s, 2H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 165.7, 157.4, 137.0, 136.1, 135.8, 132.8, 131.3, 129.7, 129.24, 129.21, 118.6, 62.5, 45.0, 44.0, 38.4, 32.0, 30.4, 24.9, 17.8, 17.5; [M+H]⁺ = 412.1; HRMS (ESI): m/z calcd for (C₂₀H₂₆N₇OS): 412.1914; found: 412.1916.

4-(furan-2-ylmethyl)-5-methyl-5-(1-pentyl-1H-tetrazol-5-yl)thiomorpholin-3-one (20d)

white solid (m.p. 134–135 °C); 63% yield (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.25 – 7.21 (m, 1H), 6.32 – 6.22 (m, 1H), 6.16 – 6.11 (m, 1H), 4.39 (d, J = 15.4 Hz, 1H), 4.28 (d, J = 15.4 Hz, 1H), 4.18 – 4.04 (m, 1H), 3.86 – 3.73 (m, 1H), 3.50 (q, J = 17.2 Hz, 2H), 3.22 (d, J = 14.3 Hz, 1H), 2.95 (d, J = 14.3 Hz, 1H), 2.20 (s, 3H), 2.06 – 1.91 (m, 2H), 1.44 – 1.28 (m, 4H), 0.93 (t, J = 6.7 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 165.5, 155.4, 149.7, 141.7, 110.8, 109.7, 61.8, 48.8, 41.3, 39.0, 32.5, 29.2, 28.9, 2637, 22.1, 13.8; [M+H]⁺ = 350.2; HRMS (ESI): m/z calcd for (C₁₆H₂₄N₅O₂S): 350.16452; found: 350.1645.

4-cyclopropyl-5-methyl-5-(1-(naphthalen-2-yl)-1H-tetrazol-5-yl)thiomorpholin-3-one (20e)

light tangerine solid (m.p. 164–165 °C); 59% (three steps);¹H NMR (400 MHz, CDCl₃) δ ppm 8.06 (d, J = 8.7 Hz, 1H), 7.99 (d, J = 7.5 Hz, 1H), 7.93 (d, J = 9.6 Hz, 2H), 7.76 – 7.61 (m, 2H), 7.44 (dd, J = 8.7, 1.6 Hz, 1H), 3.22 (d, J = 16.2 Hz, 1H), 2.94 (dd, J = 15.0, 5.9 Hz, 2H), 2.84 (d, J = 14.0 Hz, 1H), 2.44 – 2.32 (m, 1H), 2.07 (s, 3H), 1.03 – 0.87 (m, 2H), 0.80 – 0.68 (m, 1H), 0.67 – 0.54 (m, 1H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 167.5, 158.0, 133.8, 132.5, 131.6, 130.2, 128.6, 128.5, 128.2, 128.1, 126.4, 123.3, 63.0, 38.4, 31.4, 28.5, 26.2, 9.0, 7.7; [M+H]⁺ = 366.1; HRMS (ESI): m/z calcd for (C₁₉H₂₀N₅OS): 366.1383; found: 366.1383.

6-(1-cyclopentyl-1H-tetrazol-5-yl)-1-(2,5-dimethoxybenzyl)-6-methyl-4-(methylsulfonyl)piperazin-2-one (22a)

viscous liquid; 12% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 6.83 (s, 1H), 6.80 – 6.66 (m, 2H), 4.98 (d, J = 16.3 Hz, 1H), 4.77 – 4.67 (m, 1H), 4.26 (d, J = 16.8 Hz, 1H), 4.10 – 3.95 (m, 2H), 3.89 (d, J = 12.9 Hz, 1H), 3.75 (s, 3H), 3.65 (s, 3H), 3.47 (d, J = 12.9 Hz, 1H), 2.77 (s, 3H), 2.31 – 2.17 (m, 1H), 2.14 – 1.96 (m, 5H), 1.85 (s, 3H), 1.78 – 1.65 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 165.2, 154.4, 153.6, 150.3, 126.0, 115.4, 112.1, 110.8, 60.8, 60.4, 55.7, 55.6, 54.0, 49.0, 42.0, 35.9, 35.2, 34.2, 25.2, 25.1, 24.4; [M+H]⁺ = 479.2; HRMS (ESI): m/z calcd for (C₂₁H₃₁N₆O₅S): 479.2071; found: 479.2066.

6-(1-benzyl-1H-tetrazol-5-yl)-6-methyl-4-(methylsulfonyl)-1-(thiophen-2-ylmethyl)piperazin-2-one (22b)

viscous liquid; 25% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.42 – 7.32 (m, 3H), 7.28 – 7.22 (m, 1H), 7.07 (d, J = 7.4 Hz, 2H), 6.88 – 6.80 (m, 1H), 6.43 – 6.36 (m, 1H), 5.30 (d, J = 16.1 Hz, 1H), 4.96 (d, J = 16.2 Hz, 1H), 4.51 (d, J = 15.3 Hz, 1H), 4.41 (d, J = 15.3 Hz, 1H), 4.18 (d, J = 16.7 Hz, 1H), 3.75 (d, J = 16.7 Hz, 1H), 3.34 (d, J = 12.7 Hz, 1H), 3.11 (d, J = 12.7 Hz, 1H), 2.52 (s, 3H), 2.04 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 164.5, 154.0, 138.4, 133.5, 129.5, 129.2, 127.6, 127.5, 127.2, 127.1, 126.4, 59.5, 52.0, 51.7, 49.0, 43.1, 35.1, 24.0; [M+H]⁺ = 447.0; HRMS (ESI): m/z calcd for (C₁₉H₂₃N₆O₃S₂): 447.1268; found: 447.1265.

1-(furan-2-ylmethyl)-6-methyl-4-(methylsulfonyl)-6-(1-pentyl-1H-tetrazol-5-yl)piperazin-2-one (22c)

viscous liquid; 48% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.25 – 7.21 (m, 1H), 6.30 – 6.25 (m, 1H), 6.19 (d, J = 3.2 Hz, 1H), 4.60 (d, J = 15.7 Hz, 1H), 4.36 (d, J = 15.7 Hz, 1H), 4.17 (d, J = 16.7 Hz, 1H), 4.13 – 4.07 (m, 1H), 4.01 (d, J = 16.7 Hz, 1H), 3.96 – 3.85 (m, 1H), 3.81 (d, J = 12.9 Hz, 1H), 3.50 (d, J = 13.0 Hz, 1H), 2.80 (s, 3H), 2.07 (s, 3H), 2.04 – 1.92 (m, 2H), 1.45 – 1.29 (m, 4H), 0.92 (t, J = 6.8 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 164.3, 154.3, 149.1, 142.1, 110.8, 110.0, 59.4, 53.5, 49.2, 49.0, 39.8, 36.1, 29.2, 28.8, 24.4, 22.1, 13.8; [M+H]⁺ = 410.9; HRMS (ESI): m/z calcd for (C₁₇H₂₇N₆O₄S): 411.1809; found: 411.1803.

6-(1-(2,6-dimethylphenyl)-1H-tetrazol-5-yl)-1-(4-fluoro-benzyl)-6-methyl-4-(methylsulfonyl)piperazin-2-one (22d)

viscous liquid; 47% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.43 (td, J = 7.7, 2.5 Hz, 1H), 7.34 – 7.20 (m, 2H), 7.12 – 7.05 (m, 2H), 6.96 (td, J = 8.7, 2.7 Hz, 2H), 4.99 (d, J = 16.1 Hz, 1H), 4.23 – 4.08 (m, 2H), 4.05 (d, J = 13.0 Hz, 1H), 3.58 (d, J = 16.2 Hz, 1H), 3.37 (d, J = 13.0 Hz, 1H), 2.81 (s, 3H), 2.04 (s, 3H), 1.96 (s, 3H), 1.31 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 165.6, 160.7, 156.4, 135.6, 135.5, 133.1, 132.9, 131.4, 129.3, 129.1, 128.5, 128.4, 115.7, 115.5, 60.2, 53.9, 48.4, 47.3, 37.9, 22.8, 17.7, 17.6; [M+H]⁺ = 472.8; HRMS (ESI): m/z calcd for (C₂₂H₂₆FN₆O₃S): 473.1766; found: 473.1761.

6-(1-isopropyl-1H-tetrazol-5-yl)-6-methyl-4-(methylsulfo-nyl)-1-(3-(trifluoromethyl)benzyl)piperazin-2-one (22e)

viscous liquid; 43% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.53 (d, J = 7.6 Hz, 1H), 7.48 – 7.41 (m, 2H), 7.38 (d, J = 7.7 Hz, 1H), 5.40 (d, J = 16.1 Hz, 1H), 4.69 – 4.58 (m, 1H), 4.30 (d, J = 16.9 Hz, 1H), 4.12 – 3.94 (m, 2H), 3.82 (d, J = 16.1 Hz, 1H), 3.48 (d, J = 13.1 Hz, 1H), 2.77 (s, 3H), 1.78 (s, 3H), 1.68 (d, J = 6.4 Hz, 3H), 1.62 (d, J = 6.6 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 165.4, 153.8, 138.5, 130.5, 129.3, 124.5, 123.7, 60.6, 53.5, 53.3, 48.8, 47.9, 35.9, 24.8, 23.8, 23.0; [M+H]⁺ = 461.2; HRMS (ESI): m/z calcd for (C₁₈H₂₄F₃N₆O₃S): 461.1577; found: 461.1582.

6-(1-cyclohexyl-1H-tetrazol-5-yl)-1-(4-methoxybenzyl)-6-methyl-4-(methylsulfonyl)piperazin-2-one (22f)

viscous liquid; 41% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.11 (d, J = 8.1 Hz, 2H), 6.81 (d, J = 8.4 Hz, 2H), 5.26 (d, J = 15.4 Hz, 1H), 4.28 (d, J = 16.7 Hz, 1H), 4.22 – 4.11 (m, 1H), 4.01 (d, J = 16.7 Hz, 1H), 3.89 (d, J = 12.9 Hz, 1H), 3.78 (s, 3H), 3.59 (d, J = 15.4 Hz, 1H), 3.41 (d, J = 12.9 Hz, 1H), 2.78 (s, 3H), 2.17 – 1.88 (m, 4H), 1.81 (s, 3H), 1.48 – 1.20 (m, 4H), 0.95 – 0.78 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 164.9, 159.0, 154.0, 129.4, 128.6, 114.1, 60.6, 60.5, 55.3, 54.0, 49.3, 47.6, 35.4, 34.0, 33.5, 29.7, 25.7, 25.5, 24.6; [M+H]⁺ = 463.2; HRMS (ESI): m/z calcd for (C₂₁H₃₁N₆O₄S): 463.2122; found: 463.2118.

6-(1-cyclopentyl-1H-tetrazol-5-yl)-5-(2,5-dimethoxybenzyl)-6-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one (24a)

light brown solid (m.p. 171–172 °C); 38% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.61 – 7.58 (m, 1H), 7.03 (d, J = 2.6 Hz, 1H), 7.01 – 6.98 (m, 1H), 6.75 (dd, J = 9.0, 2.9 Hz, 1H), 6.69 (d, J = 8.9 Hz, 1H), 5.04 (d, J = 15.8 Hz, 1H), 4.76 (d, J = 13.3 Hz, 1H), 4.76 – 4.67 (m, 1H), 4.43 (d, J = 13.3 Hz, 1H), 4.38 (d, J = 15.8 Hz, 1H), 3.73 (s, 3H), 3.58 (s, 3H), 2.09 – 1.92 (m, 4H), 1.89 (s, 3H), 1.86 – 1.76 (m, 2H), 1.72 – 1.58 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 158.9, 153.7, 153.5, 150.6, 140.5, 133.0, 126.0, 116.0, 113.2, 111.0, 109.2, 60.8, 59.9, 55.8, 55.7, 55.6, 55.5, 40.2, 35.1, 33.5, 24.9, 24.1; [M+H]⁺ =438.3; HRMS (ESI): m/z calcd for (C₂₂H₂₈N₇O₃): 438.2248; found: 438.2242.

6-(1-(2,6-dimethylphenyl)-1H-tetrazol-5-yl)-5-(4-fluoro-benzyl)-6-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one (24b)

white solid (m.p. 163–164 °C); 42% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.51 – 7.48 (m, 1H), 7.45 (t, J = 7.6 Hz, 1H), 7.31 (t, J = 7.2 Hz, 1H), 7.26 (d, J = 8.2 Hz, 1H), 7.19 (dd, J = 7.4, 5.5 Hz, 2H), 7.05 – 6.93 (m, 2H), 6.86 (d, J = 1.4 Hz, 1H), 5.41 (d, J = 16.4 Hz, 1H), 4.76 (d, J = 13.7 Hz, 1H), 4.29 (d, J = 13.7 Hz, 1H), 3.87 (d, J = 16.4 Hz, 1H), 1.89 (s, 5H), 1.63 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 163.2, 160.7, 158.7, 156.5, 140.4, 136.1, 136.0, 134.1, 133.2, 132.3, 131.5, 129.3, 128.4, 115.7, 115.5, 109.0, 105.5, 59.8, 55.7, 45.6, 23.7, 17.7, 17.5; [M+H]⁺ = 432.2; HRMS (ESI): m/z calcd for (C₂₃H₂₃FN₇O): 432.19426; found: 432.19474.

5-(furan-2-ylmethyl)-6-methyl-6-(1-pentyl-1H-tetrazol-5-yl)-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one (24c)

viscous liquid; 38% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.62 – 7.57 (m, 1H), 7.28 – 7.25 (m, 1H), 7.00 – 6.97 (m, 1H), 6.34 – 6.24 (m, 1H), 6.15 – 6.10 (m, 1H), 4.76 – 4.63 (m, 2H), 4.57 – 4.46 (m, 2H), 4.04 – 3.90 (m, 1H), 3.88 – 3.73 (m, 1H), 2.08 (s, 3H), 1.92 – 1.79 (m, 1H), 1.77 – 1.63 (m, 1H), 1.40 – 1.17 (m, 4H), 0.88 (t, J = 6.9 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 157.8, 153.8, 149.4, 142.2, 140.6, 132.8, 110.9, 109.7, 109.4, 59.1, 55.3, 48.8, 39.1, 29.4, 28.6, 23.9, 22.0, 13.7; [M+H]⁺ = 370.1; HRMS (ESI): m/z calcd for (C₁₉H₂₂N₅O₂): 352.1768; found: 352.1772.

6-(1-isopropyl-1H-tetrazol-5-yl)-6-methyl-5-(3-(trifluoro-methyl)benzyl)-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one (24d)

white solid (m.p. 187–188 °C); 37% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.57 (t, J = 1.9 Hz, 1H), 7.56 – 7.49 (m, 2H), 7.44 (t, J = 7.6 Hz, 1H), 7.39 (d, J = 7.7 Hz, 1H), 6.98 (t, J = 2.0 Hz, 1H), 5.38 (d, J = 16.1 Hz, 1H), 4.83 (d, J = 13.6 Hz, 1H), 4.61 – 4.52 (m, 2H), 4.25 (d, J = 16.1 Hz, 1H), 1.90 (s, 3H), 1.52 (d, J = 6.5 Hz, 3H), 1.42 (d, J = 6.5 Hz, 3H). ¹³C NMR (100 MHz, CDCl₃) δ ppm 159.0, 153.4, 140.7, 140.6, 138.9, 132.8, 130.7, 129.4, 124.6, 124.1, 124.1, 109.5, 60.1, 55.6, 53.1, 46.7, 24.4, 23.6, 22.8; [M+H]⁺ = 420.2; HRMS (ESI): m/z calcd for (C₁₉H₂₁F₃N₇O): 420.1754; found: 420.1751.

6-(1-(2,6-dimethylphenyl)-1H-tetrazol-5-yl)-5-(4-methoxy-benzyl)-6-methyl-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one (24e)

viscous liquid; 23% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.49 (d, J = 2.0 Hz, 1H), 7.44 (t, J = 7.6 Hz, 1H), 7.30 (d, J = 7.6 Hz, 1H), 7.25 (d, J = 8.2 Hz, 1H), 7.12 (d, J = 8.6 Hz, 2H), 6.85 (d, J = 2.0 Hz, 1H), 6.81 (d, J = 8.7 Hz, 2H), 5.35 (d, J = 16.2 Hz, 1H), 4.80 (d, J = 13.6 Hz, 1H), 4.28 (d, J = 13.6 Hz, 1H), 3.76 (s, 3H), 3.75 (d, J = 16.2 Hz, 1H), 1.89 (d, J = 12.0 Hz, 6H), 1.64 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 158.8, 158.7, 156.7, 140.3, 136.2, 135.9, 133.3, 132.3, 131.5, 130.4, 129.3, 128.1, 114.1, 108.9, 59.7, 55.9, 55.3, 45.6, 23.8, 17.7, 17.5; [M+H]⁺ = 443.8; HRMS (ESI): m/z calcd for (C₂₄H₂₆N₇O₂): 444.21425; found: 444.215.

5-(1-cyclopentyl-1H-tetrazol-5-yl)-4-(2,5-dimethoxybenzyl)-5-methyl-1,4-thiazepan-3-one (29a)

viscous liquid; 39% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.23 (d, J = 2.6 Hz, 1H), 6.86 – 6.76 (m, 2H), 5.39 (d, J = 16.4 Hz, 1H), 4.84 – 4.72 (m, 1H), 4.54 (d, J = 16.3 Hz, 1H), 4.06 – 3.93 (m, 1H), 3.81 (s, 3H), 3.80 (s, 3H), 3.15 (d, J = 15.0 Hz, 1H), 2.82 – 2.61 (m, 3H), 2.32 – 1.89 (m, 7H), 1.83 – 1.66 (m, 2H), 1.70 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 174.3, 157.7, 153.8, 145.0, 126.5, 114.0, 111.8, 60.1, 58.9, 56.0, 55.9, 41.4, 39.6, 34.6, 34.3, 30.1, 27.3, 25.1, 25.1; [M+H]⁺ = 432.2; HRMS (ESI): m/z calcd for (C₂₁H₃₀N₅O₃S): 432.20639; found: 432.2064.

5-(1-benzyl-1H-tetrazol-5-yl)-5-methyl-4-(thiophen-2-ylmethyl)-1,4-thiazepan-3-one (29b)

white solid (m.p. 192–193 °C); 46% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.43 – 7.31 (m, 3H), 7.26 – 7.22 (m, 1H), 7.13 – 7.01 (m, 2H), 6.93 – 6.87 (m, 1H), 6.80 – 6.74 (m, 1H), 5.42 (d, J = 15.8 Hz, 1H), 5.32 – 5.12 (m, 2H), 4.39 (d, J = 15.6 Hz, 1H), 3.59 – 3.44 (m, 1H), 3.12 (d, J = 15.3 Hz, 1H), 2.76 (d, J = 15.3 Hz, 1H), 2.67 – 2.52 (m, 2H), 2.00 – 1.87 (m, 1H), 1.81 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 172.9, 157.9, 139.5, 133.2, 129.2, 129.1, 127.1, 127.0, 126.4, 126.3, 59.3, 51.8, 44.0, 39.0, 33.9, 28.2, 26.1; [M+H]⁺ = 400.2; HRMS (ESI): m/z calcd for (C₁₉H₂₂N₅OS₂): 400.12603; found: 400.12546.

4-(furan-2-ylmethyl)-5-methyl-5-(1-pentyl-1H-tetrazol-5-yl)-1,4-thiazepan-3-one (29c)

viscous liquid; 38% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.39 – 7.34 (m, 1H), 6.50 – 6.43 (m, 1H), 6.40 – 6.37 (m, 1H), 5.08 (d, J = 15.8 Hz, 1H), 4.55 (d, J = 15.8 Hz, 1H), 4.02 (t, J = 7.7 Hz, 2H), 3.97 – 3.83 (m, 1H), 3.04 (d, J = 14.8 Hz, 1H), 2.87 (dt, J = 14.8, 3.9 Hz, 1H), 2.64 (dt, J = 14.6, 4.4 Hz, 1H), 2.56 (d, J = 14.8 Hz, 1H), 2.14 (ddd, J = 15.1, 11.2, 4.0 Hz, 1H), 1.93 (s, 3H), 1.98 – 1.77 (m, 2H), 1.41 – 1.18 (m, 4H), 0.90 (t, J = 7.2 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 173.2, 157.7, 150.5, 141.6, 112.0, 110.0, 58.4, 48.6, 40.8, 39.5, 34.4, 30.5, 29.1, 28.7, 27.0, 22.1, 13.8; [M+H]⁺ = 364.2; HRMS (ESI): m/z calcd for (C₁₇H₂₆N₅O₂S): 364.18017; found: 364.18077.

5-(1-(2,6-dimethylphenyl)-1H-tetrazol-5-yl)-4-(4-methoxy-benzyl)-5-methyl-1,4-thiazepan-3-one (29d)

white solid (m.p. 182–184 °C); 27% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.45 (t, J = 7.6 Hz, 1H), 7.33 – 7.27 (m, 2H), 7.05 (d, J = 8.3 Hz, 2H), 6.80 (d, J = 8.6 Hz, 2H), 5.09 (d, J = 16.3 Hz, 1H), 3.89 – 3.79 (m, 1H), 3.76 (s, 3H), 3.16 – 2.97 (m, 3H), 2.88 (dd, J = 15.0, 6.9 Hz, 1H), 2.76 (dd, J = 12.5, 5.7 Hz, 1H), 2.20 – 2.08 (m, 1H), 1.94 (s, 3H), 1.93 (s, 3H), 1.61 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 173.2, 159.3, 158.5, 136.6, 135.9, 132.5, 131.2, 130.6, 129.3, 129.1, 127.7, 114.0, 58.7, 55.2, 47.1, 41.3, 36.6, 33.8, 28.6, 18.0, 17.9; [M+H]⁺ = 438.0; HRMS (ESI): m/z calcd for (C₂₃H₂₈N₅O₂S): 438.19582; found: 438.19671.

5-(1-isopropyl-1H-tetrazol-5-yl)-5-methyl-4-(3-(trifluoro-methyl)benzyl)-1,4-thiazepan-3-one (29e)

viscous liquid; 38% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.74 (s, 1H), 7.67 (d, J = 7.6 Hz, 1H), 7.58 (d, J = 7.8 Hz, 1H), 7.52 (t, J = 7.7 Hz, 1H), 5.58 (d, J = 16.0 Hz, 1H), 4.63 – 4.49 (m, 1H), 4.39 (d, J = 15.9 Hz, 1H), 4.00 (ddd, J = 14.5, 11.2, 2.9 Hz, 1H), 3.17 (d, J = 15.0 Hz, 1H), 2.86 – 2.68 (m, 2H), 2.69 (d, J = 15.0 Hz, 1H), 2.16 – 2.05 (m, 1H), 1.76 (s, 3H), 1.62 – 1.48 (m, 6H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 174.2, 156.8, 138.9, 131.1, 131.0, 129.4, 125.3, 124.5, 122.6, 59.1, 52.2, 47.6, 39.5, 34.5, 30.1, 27.2, 23.2, 23.1; [M+H]⁺ = 302.1; HRMS (ESI): m/z calcd for (C₁₈H₂₃N₅OS): 414.15699; found: 414.15684.

5-(1-cyclopentyl-1H-tetrazol-5-yl)-4-(2,5-dimethoxybenzyl)-4,5-dihydrobenzo[f][1,4]oxazepin-3(2H)-one (31a)

viscous liquid; 23% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.40 (tt, J = 8.0, 1.9 Hz, 1H), 7.21 – 7.05 (m, 3H), 6.87 – 6.77 (m, 3H), 5.62 (s, 1H), 5.39 (d, J = 15.1 Hz, 1H), 4.98 (d, J = 16.7 Hz, 1H), 4.43 (d, J = 16.7 Hz, 2H), 4.15 – 4.03 (m, 1H), 3.74 (s, 3H), 3.67 (s, 3H), 2.15 – 1.85 (m, 3H), 1.85 – 1.72 (m, 1H), 1.66 – 1.63 (m, 1H), 1.50 – 1.32 (m, 1H), 1.30 – 1.22 (m, 1H), 1.18 – 1.05 (m, 1H);¹³C NMR (100 MHz, CDCl₃) δ ppm 169.8, 157.6, 153.8, 153.5, 151.8, 132.0, 130.6, 128.7, 125.1, 122.1, 115.9, 114.3, 111.8, 110.0, 73.4, 59.6, 56.1, 55.7, 55.6, 47.1, 32.9, 32.8, 24.5, 24.3; [M+H]⁺ = 450.3; HRMS (ESI): m/z calcd for (C₂₄H₂₈N₅O₄): 450.2136; found: 450.213.

4-cyclopropyl-5-(1-(naphthalen-2-yl)-1H-tetrazol-5-yl)-4,5-dihydrobenzo[f][1,4]oxazepin-3(2H)-one (31b)

viscous liquid; 20% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.88 (d, J = 7.7 Hz, 1H), 7.78 (d, J = 8.7 Hz, 1H), 7.72 (d, J = 7.6 Hz, 1H), 7.66 – 7.56 (m, 1H), 7.40 (d, J = 2.0 Hz, 1H), 7.10 (td, J = 7.6, 2.0 Hz, 1H), 7.00 (dd, J = 8.6, 2.1 Hz, 2H), 6.97 (d, J = 8.0 Hz, 2H), 6.60 – 6.45 (m, 2H), 5.63 (s, 1H), 4.92 (d, J = 16.5 Hz, 1H), 4.33 (d, J = 16.5 Hz, 1H), 3.08 – 2.97 (m, 1H), 1.05 – 0.76 (m, 5H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 171.25, 156.90, 156.02, 133.45, 132.38, 131.43, 130.51, 130.04, 129.75, 128.83, 128.18, 128.13, 127.89, 127.67, 125.42, 124.35, 122.42, 121.38, 77.31, 76.99, 76.68, 73.58, 58.71, 33.47, 8.77, 7.83; [M+H]⁺ = 398.2; HRMS (ESI): m/z calcd for (C₂₃H₂₀N₅O₂): 398.16115; found: 398.16105.

5-(1-(2,6-dimethylphenyl)-1H-tetrazol-5-yl)-4-(4-fluoro-benzyl)-4,5-dihydrobenzo[f][1,4]oxazepin-3(2H)-one (31c)

white solid (m.p. 178–179 °C); 62% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.26 – 7.14 (m, 4H), 7.08 (d, J = 7.6 Hz, 1H), 7.04 – 6.96 (m, 3H), 6.76 (d, J = 7.6 Hz, 1H), 6.70 – 6.62 (m, 1H), 5.96 (d, J = 7.4 Hz, 1H), 5.62 (d, J = 15.3 Hz, 1H), 5.11 (dd, J = 16.8, 2.2 Hz, 1H), 5.03 (d, J = 2.2 Hz, 1H), 4.50 (dd, J = 16.8, 2.5 Hz, 1H), 4.25 (d, J = 15.3 Hz, 1H), 1.77 (s, 3H), 1.22 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 170.1, 163.7, 161.3, 157.1, 154.7, 136.9, 133.7, 131.7, 131.4, 131.3, 131.1, 130.7, 130.1, 130.0, 129.3, 128.8, 128.3, 124.8, 121.4, 115.9, 115.7, 73.3, 55.1, 50.9, 16.8, 16.4; [M+H]⁺ = 444.1; HRMS (ESI): m/z calcd for (C₂₅H₂₃FN₅O₂): 444.18303; found: 444.18303.

5-(1-isopropyl-1H-tetrazol-5-yl)-4-(3-(trifluoromethyl)benz-yl)-4,5-dihydrobenzo[f][1,4]oxazepin-3(2H)-one (31d)

viscous liquid; 55% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.63 – 7.56 (m, 1H), 7.52 – 7.42 (m, 4H), 7.24 – 7.17 (m, 1H), 7.15 (d, J = 7.7 Hz, 1H), 7.07 (d, J = 7.5 Hz, 1H), 5.83 (d, J = 16.0 Hz, 1H), 5.32 (s, 1H), 4.99 (d, J = 16.9 Hz, 1H), 4.52 (d, J = 16.9 Hz, 1H), 4.32 (d, J = 15.7 Hz, 1H), 3.97 – 3.82 (m, 1H), 1.43 (d, J = 5.6 Hz, 3H), 0.86 (d, J = 5.4 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 170.1, 157.6, 152.5, 137.1, 132.5, 131.6, 130.2, 129.4, 128.5, 125.6, 124.8, 124.5, 122.3, 73.5, 55.5, 51.5, 51.4, 22.3, 21.7; [M+H]⁺ = 432.2; HRMS (ESI): m/z calcd for (C₂₁H₂₁N₅O₂): 432.16419; found: 432.16378.

5-(1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-1H-tetrazol-5-yl)-4-isopentyl-4,5-dihydrobenzo[f][1,4]oxazepin-3(2H)-one (31e)

white solid (m.p. 209–210 °C); 27% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.31 – 7.22 (m, 1H), 7.00 (d, J = 8.0 Hz, 1H), 6.89 (td, J = 7.5, 1.1 Hz, 1H), 6.82 – 6.75 (m, 2H), 6.50 – 6.35 (m, 2H), 5.37 (s, 1H), 4.86 (dd, J = 16.6, 1.0 Hz, 1H), 4.38 – 4.18 (m, 5H), 4.16 – 4.04 (m, 1H), 3.34 – 3.21 (m, 1H), 1.65 – 1.53 (m, 1H), 1.53 – 1.43 (m, 2H), 0.92 (s, 3H), 0.91 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 169.2, 156.9, 155.5, 145.5, 143.7, 131.5, 130.4, 128.9, 126.2, 124.5, 121.5, 118.9, 117.7, 115.3, 73.3, 64.4, 64.2, 56.7, 48.3, 36.7, 25.9, 22.6, 22.5; [M+H]⁺ = 436.3; HRMS (ESI): m/z calcd for (C₂₃H₂₆N₅O₄): 436.19793; found: 436.19759.

4-(benzo[d][1,3]dioxol-5-ylmethyl)-5-(1-butyl-1H-tetrazol-5-yl)-4,5-dihydrobenzo[f][1,4]oxazepin-3(2H)-one (31f)

viscous liquid; 41% (three steps); ¹H NMR (400 MHz, CDCl₃) δ ppm 7.48 – 7.40 (m, 1H), 7.22 – 7.09 (m, 2H), 7.02 (d, J = 7.5 Hz, 1H), 6.77 (dd, J = 7.7, 2.0 Hz, 1H), 6.73 – 6.67 (m, 2H), 6.02 – 5.92 (m, 2H), 5.70 (d, J = 15.0 Hz, 1H), 5.37 (s, 1H), 4.97 (dd, J = 16.8, 1.9 Hz, 1H), 4.46 (dd, J = 16.8, 2.2 Hz, 1H), 4.06 (d, J = 15.1 Hz, 1H), 3.82 – 3.59 (m, 2H), 1.52 – 1.36 (m, 1H), 1.19 – 0.94 (m, 3H), 0.74 (t, J = 7.2 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ ppm 169.7, 157.7, 153.5, 148.2, 147.5, 132.3, 130.3, 129.5, 128.6, 125.4, 122.2, 121.9, 108.9, 108.3, 101.2, 73.5, 54.3, 51.2, 47.6, 30.9, 19.4, 13.3; [M+H]⁺ = 422.1; HRMS (ESI): m/z calcd for (C₂₂H₂₄N₅O₄): 422.18228; found: 422.8213.