Sodium tetrachloroaurate(III) dihydrate-catalyzed efficient synthesis of 1,5-benzodiazepine and quinoxaline derivatives

Ren-xin Shi; Yun-kui Liu; Zhen-yuan Xu

doi:10.1631/jzus.B0900288

. 2010 Feb;11(2):102–108. doi: 10.1631/jzus.B0900288

Sodium tetrachloroaurate(III) dihydrate-catalyzed efficient synthesis of 1,5-benzodiazepine and quinoxaline derivatives^{^*}

Ren-xin Shi ¹, Yun-kui Liu ^1,^†, Zhen-yuan Xu ^1,^†,^‡

PMCID: PMC2816313 PMID: 20104644

Abstract

Both 1,5-benzodiazepine and quinoxaline derivatives are important heterocycles in pharmaceuticals. We describe an efficient and clean method for the synthesis of 1,5-benzodiazepines from o-phenylenediamine and ketones catalyzed by sodium tetrachloroaurate(III) dihydrate under mild conditions. The catalyst was shown to be equally effective for the synthesis of quinoxalines from o-phenylenediamine and α-bromo ketones under the similar reaction conditions. This method produced good yields.

Keywords: 1,5-benzodiaepines; o-phenylenediamine; Ketones; Quinoxalines; Gold catalyst

1. Introduction

Benzodiazepines and quinoxalines have recently received much attention as important classes of heterocyclic compounds in pharmaceuticals. The benzodiazepine derivatives have been found to have wide applications in medical chemistry, such as anti-convulsant, anti-anxiety, analgesic, hypnotic, sedative, antidepressant and anti-inflammatory agents (Smalley, 1979; Landquist, 1984; Randall and Kappel, 1973). In addition, 1,5-benzodiazepines are intermediates used for the synthesis of other fused ring compounds such as triazolo-, oxazino- or furano-benzodiazepines (Essaber et al., 1998; El-snyed et al., 1999; Xu et al., 1999; Zhang et al., 1999; Reddy et al., 2000). On the other hand, quinoxaline derivatives have also shown a broad spectrum of biological activities, which has led them to be privileged structures in drug discovery (Zaragoza and Stephensen, 1999; Wu and Ede, 2001).

To date, several methods for the preparation of 1,5-benzodiazepines have been reported in the literatures, including condensation reactions of o-phenylenediamine with α,β-unsaturated carbonyl compounds (Ried and Stahlofen, 1957), β-haloketones (Ried and Torinus, 1959) or ketones promoted by BF₃·Et₂O (Herbert and Suschitzky, 1974), NaBH₄ (Morales et al., 1986), polyphosphoric acid or SiO₂, (Jung et al., 1999), MgO/POCl₃ (Balakrishna and Kaboudin, 2001), Yb(OTf)₃ (Curini et al., 2001), Al₂O₃/P₂O₅ or AcOH under microwave (Kaboudin and Navaee, 2001), ionic liquid (Jarikote et al., 2003), SmI₂ (Luo et al., 2005), HBF₄-SiO₂ (Bandgar et al., 2006), dodecyl sulfonic acid (Sharma et al., 2007), AgNO₃ (Kumar et al., 2006), H₁₄[NaP₅W₃₀O₁₁₀] (Heravi et al., 2007a), polyaniline-sulfate salt (Srinivas et al., 2007), and 2,4,6-trichloro-1,3,5-triazine (Kuo et al., 2008). Meanwhile, a number of methods have also been developed for the synthesis of quinoxalines, involving condensation of 1,2-diamines with 1,2-dicarbonyl compounds (Kaupp and Naimi-Jamal, 2002; More et al., 2005; 2006; Bhosale et al., 2005; Heravi et al., 2007b), 1,4-addition of 1,2-diamines with 1,2-diaza-1,3-butadienes (Aparicio et al., 2006), oxidation-trapping of α-hydroxy ketones with 1,2-diamine (Raw et al., 2004; Kim et al., 2005; Robinson and Taylor, 2005), cyclization-oxidation of polymer-linked 2-nitrophenyl carbamate with α-bromo ketones (Singh et al., 2003), and oxidative-coupling of epoxides with o-phenylenediamine (Antoniotti and Duñach, 2002). However, many of these procedures for the syntheses of 1,5-benzodiazepines and quinoxalines have limitations, i.e., harsh reaction conditions, high catalyst loading, occurrence of several side products, tedious work-up procedures, use of toxic and/or hazardous transition metals, and so on. Therefore, the development of clean and efficient methods for the syntheses of these valuable compounds is desirable.

Gold is a soft transition metal showing high electrophilic affinity to alkynes, alkenes, and allenes (Hashmi and Hutchings, 2006; Gorin and Toste, 2007; Hashmi, 2007; Hashmi and Rudolph, 2008; Li et al., 2008). It can also act as a Lewis acid for the activation of electrophiles (Arcadi et al., 2006). Recently, there has been growing interest in gold-catalyzed organic transformations because gold catalysts usually exhibit extraordinary reactivity and show high selectivity in the reactions. Besides, gold catalysts are quite robust, and most of the reactions tolerate both oxygen and acidic protons; thus, neither air nor humidity needs to be excluded. As part of our ongoing interest in the gold-catalyzed transformations (Liu et al., 2009a; 2009b), we herein described clean and efficient syntheses of 1,5-benzodiazepines and quinoxaline derivatives using sodium tetrachloroaurate(III) dihydrate as catalyst under mild reaction conditions.

2. Materials and methods

A representative procedure for the synthesis of 1,5-benzodiazepines 3 or quinoxalines 5 is described as follows: to a 25-ml flask, o-phenylenediamine 1 (0.11 g, 1.0 mmol), NaAuCl₄·2H₂O (0.008 g, 0.02 mmol), ketones 2 (2.2 mmol, for synthesis of 3) or α-bromo ketones 4 (1.2 mmol, for synthesis of 5), and EtOH (5 ml) were added. The mixture was stirred at room temperature for the given time in Table 2 (for 3) or Table 3 (for 5). Upon completion, the solvent was removed under vacuum. The residue was purified by chromatography using cyclohexane/ethyl acetate (6:1, v/v) as eluent to afford 1,5-benzodiazepines 3 or quinoxalines 5.

Table 2.

Synthesis of various 1,5-benzodiazepines 3 from o-phenylenediamine 1 and ketones 2 catalyzed by NaAuCl₄·2H₂O^a

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Table 3.

Synthesis of various quinoxalines 5 from o-phenylenediamine 1 and α-bromo ketones 4 catalyzed by NaAuCl₄·2H₂O^a

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3. Results and discussion

Initially, the reaction of o-phenylenediamine 1 with acetone 2e was tested as a model reaction for optimization of the reaction conditions (Table 1). In the absence of a gold catalyst, the reaction could hardly take place (Entry 1). The reaction proceeded smoothly to give the desired product 3e in 80% yield when 1 and 2e were treated with 2% (mole fraction) of AuCl₃ at room temperature for 5 h (Entry 2). Under the catalysis of HAuCl₄·4H₂O, the yield of 3e was increased to be 85% (Entry 3). So far, the best result was obtained by using NaAuCl₄·2H₂O as a catalyst, which gave 3e in 95% yield (Entry 4). Solvent screening experiments showed that ethanol is the best choice for the reaction (Entries 4–8). It is noteworthy that the reaction could still proceed well even in water or solvent-free condition (Entries 9 and 10).

Table 1.

Optimization of reaction condition^a

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With optimized conditions in hand, a variety of substrates were used in this reaction to establish the generality and efficiency (Fig. 1, Table 2). In most cases, the reaction proceeded smoothly to give 3 in good to excellent yields under mild conditions. Reactions of o-phenylenediamine with acetophenones possessing electron-withdrawing groups generally gave better yield of 3 than those containing electron-donating groups (Entries 4 vs. 2, 3). Both acyclic and cyclic alkylketones were suitable substrates for the reaction (Entries 5–10). Note that lower yields were obtained from the more hindered alkylketones (Entries 5–7 vs. 8). The condensation of 2-butanone 2f or 4-methyl 2-pentanone 2g with o-phenylenediamine selectively gave 3f or 3g, respectively (Entries 6 and 7), along with small amount of the diastereoisomer 3f′ or 3g′.

Encouraged by the successful application of NaAuCl₄·2H₂O as a catalyst in the synthesis of 1,5-benzodiazepines, we expected that quinoxalines 5 will be obtained if o-phenylenediamine 1 is allowed to react with α-bromo ketones 4 (Das et al., 2007). Indeed, when 1 equivalent of 1 was treated with 1.2 equivalents of 4 in ethanol under similar reaction conditions, quinoxalines 5 were produced in high yields (Fig. 2, Table 3). Control experiment showed that much lower yield of 5a (33%) was obtained in the absence of the gold catalyst (Entry 1). A variety of aromatic ring-tethered α-bromo ketones were investigated to establish the scope and generality of the reaction, and in all cases quinoxalines 5 were produced in good to excellent yields in the presence of NaAuCl₄·2H₂O under mild reaction conditions. In the reaction, gold catalyst may act as a bifunctional catalyst; namely, it serves as a Lewis acid catalyst to help the cyclization process via activation of the carbonyl group (Yang et al., 2007) as well as an oxidative catalyst for the dehydrogenation of the in situ generated dihydroquinoxalines with dioxygen (Zhu and Angelici, 2007; Liu et al., 2009a).

Fig. 2 — Synthesis of quinoxalines 5 using NaAuCl₄·2H₂O as catalyst

4. Conclusion

In summary, we described a clean and efficient protocol for syntheses of 1,5-benzodiazepines and quinoxalines. The advantages of the present method lie in relatively low catalyst loading, mild reaction conditions, simple operation, and good yields.

5. Experimental details

All the starting chemicals were commercial products (Aldrich or J & K Chemica). Melting points were measured on a Büchi B-545 and uncorrected. Infrared (IR) spectra were recorded on a Bruker EQUINOX 55 spectrometer. ¹H NMR and ¹³C NMR spectra were obtained on a Bruker AVANCE III 500 (500 MHz) instrument in CDCl₃ using tetramethylsilane (TMS) as internal standard. Chemical shifts (δ) are expressed in ×10⁻⁶ and coupling constants (J) are given in Hz. Mass spectra were obtained on an HP 5989B mass spectrometer. Gas chromatograph-mass spectrometer (GC-MS) experiments were performed with an Agilent 6890N GC system equipped with a 5973N mass-selective detector.

2-methyl-2,4-diphenyl-2,3-dihydro-1H-1,5-benzodiazepine (3a): yellow solid, m.p. 151–152 °C [152–153 °C (Mahajan et al., 2008)]; ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 1.77 (s, 3H, CH₃), 2.98 (d, J=12.8 Hz, 1H, CH^a), 3.15 (d, J=12.8 Hz, 1H, CH^b), 3.55 (br s, 1H, NH), 6.85–7.60 (m, 14H, ArH); IR (KBr): ν _max (cm⁻¹) 3325, 1632, 1595; MS (70 eV): m/z (%)=312 (18%) [M⁺].

2-methyl-2,4-di(4-methylphenyl)-2,3-dihydro-1H-1,5-benzodiazepine (3b): yellow solid, m.p. 141–143 °C [142–144 °C (Kuo et al., 2006)]; ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 2.25–2.31 (m, 9H, CH₃), 2.95 (d, J=13.2 Hz, 1H, CH^a), 3.06 (d, J=13.2 Hz, 1H, CH^b), 3.52 (br s, 1H, NH), 6.81–7.56 (m, 12H, ArH); IR (KBr): ν _max (cm⁻¹) 3270, 1644, 1601; MS (70 eV): m/z (%)=340 (14%) [M⁺].

2-methyl-2,4-di(4-methoxylphenyl)-2,3-dihydro-1H-1,5-benzodiazepine (3c): yellow solid, m.p. 119–120 °C [(120–121 °C (Reddy et al., 2007)]; ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 1.76 (s, 3H, CH₃), 2.95 (d, J=13.2 Hz, 1H, CH^a), 3.01 (d, J=13.2 Hz, 1H, CH^b), 3.78 (s, 3H, OCH₃), 3.88 (s, 3H, OCH₃), 6.77–7.51 (m, 12H, ArH); IR (KBr): ν _max (cm⁻¹) 3350, 1631, 1596; MS (70 eV): m/z (%)=372 (16%) [M⁺].

2-methyl-2,4-di(4-chlorophenyl)-2,3-dihydro-1H-1,5-benzodiazepine (3d): yellow solid, m.p. 159–160 °C [162–163 °C (Mahajan et al., 2008)]; ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 1.75 (s, 3H, CH₃), 2.90 (d, J=13.2 Hz, 1H, CH^a), 3.10 (d, J=13.2 Hz, 1H, CH^b), 3.47 (br s, 1H, NH), 6.84–7.53 (m, 12H, ArH); IR (KBr): ν _max (cm⁻¹) 3328, 1632, 1593; MS (70 eV): m/z (%)=380 (22%) [M⁺].

2,2,4-trimethyl-2,3-dihydro-1H-1,5-benzodiaze-pine (3e): yellow solid, m.p. 137–139 °C [136–137 °C (Mahajan et al., 2008)]; ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 1.34 (s, 6H, CH₃), 2.25 (s, 2H, CH₂), 2.39 (s, 3H, CH₃), 2.96 (br s, 1H, NH), 6.70–7.18 (m, 4H, ArH); IR (KBr): ν _max (cm⁻¹) 3335, 1642, 1593; MS (70 eV): m/z (%)=188 (28%) [M⁺].

2.4-diethyl-2-methyl-2,3-dihydro-1H-1,5-benzo-diazepine (3f): yellow solid, m.p. 139–140 °C [140–142 °C (Mahajan et al., 2008)]; ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 0.94 (t, J=7.6 Hz, 3H, CH₃), 1.25 (m, 6H, CH₃), 1.62 (m, 2H, CH₂), 2.14 (d, J=12.8 Hz, 1H, CH^a), 2.23 (d, J=12.8 Hz, 1H, CH^b), 2.59 (q, J=7.2 Hz, 2H, CH₂), 3.08 (br s, 1H, NH), 6.69–7.26 (m, 4H, ArH); IR (KBr): ν _max (cm⁻¹) 3328, 1636, 1605; MS (70 eV): m/z (%)=216 (15%) [M⁺].

2-methyl-2,4-diisobutyl-2,3-dihydro-1H-1,5-benzodiazepine (3g): yellow solid, m.p. 115–116 °C [117–119 °C (Mahajan et al., 2008)]; ¹H NMR (CDCl₃, 500 Hz): δ (×10⁻⁶) 0.96–1.02 (m, 12H), 1.33 (s, 3H), 1.50–1.54 (m, 2H), 1.72–1.76 (m, 1H), 2.13–2.24 (m, 3H), 2.46 (d, J=6.4 Hz, 2H), 3.14 (br s, 1H, NH), 6.68–7.26 (m, 4H, ArH); IR (KBr): ν _max (cm⁻¹) 3320, 1650, 1600; MS (70 eV): m/z (%)=272 (12%) [M⁺].

2,2,4-triethyl-3-methyl-2,3-dihydro-1H-1,5-benzodiazepine (3h): yellow solid, m.p. 139–140 °C [142–143 °C (Mahajan et al., 2008)]; ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 0.75–1.60 (m, 15H), 2.51 (s, 3H, CH₃), 2.82 (q, J=6.8 Hz, 1H, CH), 3.84 (br s, 1H, NH), 6.61–7.34 (m, 4H, ArH); IR (KBr): ν _max (cm⁻¹) 3322, 1639, 1595; MS (70 eV): m/z (%)=244 (26%) [M⁺].

1′,2′,3′,4′,10′,11a′-hexahydrospiro[cyclohexane-1,11′-dibenzo[b,e][1,4]diazepine] (3i): yellow solid, m.p. 133–134 °C [135–136 °C (Mahajan et al., 2008)]; ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 1.12–1.89 (m, 16H), 2.27–2.38 (m, 3H), 3.82 (br s, 1H, NH), 6.76–7.29 (m, 4H, ArH); IR (KBr): ν _max (cm⁻¹) 3290, 1640, 1600; MS (70 eV): m/z (%)=268 (23%) [M⁺].

2,3,9,10a-tetrahydro-1H-spiro[benzo[b]cyclopenta[e][1,4]diazepine-10,1′-cyclopentane] (3j): yellow solid, m.p. 135–136 °C [136–137 °C (Mahajan et al., 2008)]; ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 1.25–1.96 (m, 12H), 2.27–2.36 (m, 3H), 4.0 (br s, 1H, NH), 6.60–7.26 (m, 4H, ArH); IR (KBr): ν _max (cm⁻¹) 3338, 1660, 1598; MS (70 eV): m/z (%)=240 (28%) [M⁺].

2-phenyl quinoxaline (5a) (Das et al., 2007): ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 7.51–7.58 (m, 3H), 7.74–7.82 (m, 2H), 8.12–8.21 (m, 4H), 9.34 (s, 1H); MS (70 eV): m/z (%)=206 (100%) [M⁺].

2-(4-methylphenyl)quinoxaline (5b) (Das et al., 2007): ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 2.44 (s, 3H), 7.31 (d, J=8.0 Hz, 2H), 7.70–7.78 (m, 2H), 8.09–8.15 (m, 4H), 9.30 (s, 1H); MS (70 eV): m/z (%)=220 (100%) [M⁺].

2-(4-methoxylphenyl)quinoxaline (5c) (Das et al., 2007): ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 3.91 (s, 3H), 7.09 (d, J=8.5 Hz, 2H), 7.70–7.79 (m, 2H), 8.09–8.19 (m, 4H), 9.30 (s, 1H); MS (70 eV): m/z (%)=236 (100%) [M⁺].

2-(2-methoxylphenyl)quinoxaline (5d) (Cho and Oh, 2007): ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 3.91 (s, 3H), 7.07 (d, J=8.0 Hz, 2H), 7.17 (t, J=7.0 Hz, 1H), 7.47–7.51 (m, 1H), 7.74–7.79 (m, 2H), 7.89–7.91 (m, 1H), 8.12–8.18 (m, 2H), 9.34 (s, 1H); MS (70 eV): m/z (%)=236 (100%) [M⁺].

2-(3-methoxylphenyl)quinoxaline (5e) (Cho and Oh, 2007): ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 3.95 (s, 3H), 7.08 (d, J=8.0 Hz, 2H), 7.47 (t, J=8.0 Hz, 1H), 7.74–7.81 (m, 4H), 8.12–8.18 (m, 2H), 9.32 (s, 1H); MS (70 eV): m/z (%)=236 (100%) [M⁺].

2-(4-chlorophenyl)quinoxaline (5f) (Das et al., 2007): ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 7.54 (d, J=8.5 Hz, 2H), 7.75–7.82 (m, 2H), 8.11–8.16 (m, 4H), 9.30 (s, 1H); MS (70 eV): m/z (%)=240 (100%) [M⁺].

2-(4-bromophenyl)quinoxaline (5g) (Das et al., 2007): ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 7.70 (d, J=8.5 Hz, 2H), 7.70–7.81 (m, 2H), 8.08–8.15 (m, 4H), 9.30 (s, 1H); MS (70 eV): m/z (%)=284 (100%) [M⁺].

2-(4-fluorophenyl)quinoxaline (5h) (Das et al., 2007): ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 7.23–7.28 (m, 2H), 7.74–7.81 (m, 2H), 8.08–8.15 (m, 4H), 9.30 (s, 1H); MS (70 eV): m/z (%)=224 (100%) [M⁺].

2-(2-furyl)quinoxaline (5i) (Das et al., 2007): ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 6.64 (d, J=1.5 Hz, 1H), 7.33 (t, J=3.0 Hz, 1H), 7.69–7.78 (m, 3H), 8.07–8.12 (m, 2H), 9.26 (s,1H); MS (70 eV): m/z (%)=196 (100%) [M⁺].

2-(2-thienyl)quinoxaline (5j) (Peter et al., 2004): ¹H NMR (CDCl₃, 500 MHz): δ (×10⁻⁶) 7.21 (t, J=3.5 Hz, 1H), 7.55 (d, J=4.0 Hz, 1H), 7.68–7.77 (m, 2H), 7.86 (t, J=3.0 Hz, 1H), 8.06–8.09 (m, 2H), 9.24 (s, 1H); MS (70 eV): m/z (%)=212 (100%) [M⁺].

Footnotes

^{^*}

Project supported by the Natural Science Foundation of Zhejiang Province (No. Y407168), the Foundation of Education of Zhejiang Province (No. Z200803599), and the Opening Foundation of Zhejiang Provincial Top Key Discipline (No. 56310101634), China

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[B33] 33.Morales HR, Bulbarela A, Contreras R. New synthesis of dihydro- and tetrahydro-1,5-benzodiazepines by reductive condensation of o-phenylenediamine and ketones in the presence of sodium borohydride. Heterocycles. 1986;24(1):135–139. doi: 10.3987/R-1986-01-0135. [DOI] [Google Scholar]

[B34] 34.More SV, Sastry MNV, Wang CC, Yao CF. Molecular iodine a powerful catalyst for the easy and efficient synthesis of quinoxalines. Tetrahedron Lett. 2005;46(37):6345–6348. doi: 10.1016/j.tetlet.2005.07.026. [DOI] [Google Scholar]

[B35] 35.More SV, Sastry MNV, Yao CF. Cerium (IV) ammonium nitrate (CAN) as a catalyst in tap water: a simple, efficient and green approach to the synthesis of quinoxalines. Green Chem. 2006;8(1):91–95. doi: 10.1039/b510677j. [DOI] [Google Scholar]

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[B53] 53.Zhu B, Angelici RJ. Non-nanogold catalyzed aerobic oxidation of secondary amines to imines. Chem Commun. 2007;(21):2157–2159. doi: 10.1039/b700555e. [DOI] [PubMed] [Google Scholar]

PERMALINK

Sodium tetrachloroaurate(III) dihydrate-catalyzed efficient synthesis of 1,5-benzodiazepine and quinoxaline derivatives^{^*}

Ren-xin Shi

Yun-kui Liu

Zhen-yuan Xu

Abstract

1. Introduction