Synlett 2013; 24(12): 1485-1492
DOI: 10.1055/s-0033-1338953
letter
© Georg Thieme Verlag Stuttgart · New York

Synthesis of Highly Regioselective Bifunctional Tricyclic Tetrazole-1H-benzo[b][1,4]diazepins

Ahmad Shaabani*
a   Faculty of Chemistry, Shahid Beheshti University, G. C., P. O. Box 19396-4716, Tehran, Iran   Fax: +98(21)22431663   Email: a-shaabani@sbu.ac.ir
,
Zeinab Hezarkhani
a   Faculty of Chemistry, Shahid Beheshti University, G. C., P. O. Box 19396-4716, Tehran, Iran   Fax: +98(21)22431663   Email: a-shaabani@sbu.ac.ir
,
Hamid Mofakham
a   Faculty of Chemistry, Shahid Beheshti University, G. C., P. O. Box 19396-4716, Tehran, Iran   Fax: +98(21)22431663   Email: a-shaabani@sbu.ac.ir
,
Seik Weng Ng
b   Department of Chemistry, University of Malaya, 50603, Kuala Lumpur, Malaysia
› Author Affiliations
Further Information

Publication History

Received: 18 March 2013

Accepted after revision: 24 April 2013

Publication Date:
06 June 2013 (online)


Abstract

A new approach for the synthesis of arrays of bifunctional tricyclic tetrazole-1H-benzo[b][1,4]diazepines has been investigated. It includes a sequential two-step isocyanide-based condensation reaction of diamines or 2-nitroanilines, ethyl 3-oxobutanoate or 2,2,6-trimethyl-4H-1,3-dioxin-4-one, isocyanides and trimethylsilyl azide in good yields.

 
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  • 23 General Procedure for the Synthesis of 1H-Tetrazol-5-yl-4-methyl-1H-benzo[b][1,4]diazepines 9a–h Diamines (1.00 mmol) and ethyl 3-oxobutanoate (1.50 mmol) or 2,2,6-trimethyl-4H-1,3-dioxin-4-one (1.20 mmol) in o-xylene (2 mL) were activated by exposure to microwave irradiation (700 W, multimode reactor) for 10 min. The benzo[b][1,4]diazepines 4ac were recrystallized by cooling in o-xylene. The crystals were filtered and washed with Et2O (2 × 5 mL) and then recrystallized from acetone to give benzo[b][1,4]diazepines 4ac.18 To a solution of 1,4-diazepines 4ac (0.50 mmol) and PTSA·H2O (0.05 g, 2.50 mol%) in MeOH (5.00 mL) was added isocyanide (0.50 mmol) and trimethylsilyl azide (0.75 mmol), and the resulting mixture was stirred at r.t. After completion of the reaction, as indicated by TLC (EtOAc–n-hexane, 3:1) after 1 h, the precipitate was filtered off and washed with H2O and MeOH, and then crystallized from acetone to give products 9ah. General Procedure for the Synthesis of 1H-Tetrazol-5-yl-4-methyl-1H-benzo[b][1,4]diazepines 9a,b,d,e Ethyl 3-oxobutanoate (1.10 mmol) and 2-nitroanilines (1.00 mmol) were stirred in MeOH (2 mL) at r.t. for 1 h, and then trimethylsilyl azide (1.50 mmol) and isocyanide (1.50 mmol) were added. The reaction mixture was stirred for 48 h at r.t. until the reaction was complete (indicated by TLC).19 To this solution was added SnCl2·2H2O (5 mmol), and the resulting mixture stirred at reflux for 12 h. Then, the solvent was removed under vacuum, and the crude product was purified to give products 8ad. To a stirred solution of products 8ad in dry THF (10 mL) was added NaH as a 60% suspension in oil (0.121 g, 2.5 mmol), and the mixture was heated to reflux for 5 h. On completion, the reaction mixture was extracted with EtOAc (3 × 20 mL) and H2O (30 mL). The organic layer was cooled, dried over Na2SO4, and the solvent was removed under vacuum to give products 9a,b,d,e.20 Analytical Data 4-(1-Cyclohexyl-1H-tetrazol-5-yl)-4-methyl-4,5-dihydro-1H-benzo[b][1,4]diazepin-2(3H)-one (9a) Colorless crystals; mp >270 °C. IR (KBr): 3347, 3295, 3200, 3139, 3087, 2926, 2851, 1675, 1634, 1597, 1526, 1449, 1376 cm–1. 1H NMR (300.13 MHz, DMSO-d 6): δ = 1.00–1.80 (13 H, m, 5 CH2 of cyclohexyl and CH3), 2.65 (1 H, ABq, J = 13.9 Hz, CH2), 2.79 (1 H, ABq, J = 13.9 Hz, CH2), 5.14 (1 H, m, CH of cyclohexyl), 6.01 (1 H, s, NH), 6.80–6.97 (4 H, m, HAr), 9.84 (1 H, br s, NHCO). 13C NMR (75.47 MHz, DMSO-d 6): δ = 25.1, 25.5, 25.6, 29.2, 33.4, 33.8, 47.1, 59.1, 61.2, 122.1, 122.2, 125.2, 129.9, 137.2, 157.9, 170.0. Anal. Calcd for C17H22N6O: C, 62.56; H, 6.79; N, 25.75. Found: C, 62.52; H, 6.69; N, 25.70. 4-(1-Cyclohexyl-1H-tetrazol-5-yl)-4,7-dimethyl-4,5-dihydro-1H-benzo[b][1,4]diazepin-2(3H)-one (9b) Colorless crystals; mp 245–247 °C. IR (KBr): 3347, 3295, 3200, 3139, 3087, 2926, 2851, 1675, 1634, 1597, 1526, 1449, 1376 cm–1. 1H NMR (300.13 MHz, DMSO-d 6): δ = 1.00–1.80 (13 H, m, 5 CH2 of cyclohexyl and CH3), 2.20 (3 H, s, CH3), 2.55 (1 H, ABq, J = 14.2 Hz, CH2), 2.79 (1 H, ABq, J = 13.9 Hz, CH2), 5.12 (1 H, m, CH of cyclohexyl), 5.89 (1 H, s, NH), 6.58 (1 H, ABq, J = 7.6 Hz, H-Ar), 6.76 (H, s, HAr), 6.93 (1 H, ABq, J = 7.7 Hz, HAr), 9.75 (1 H, br s, NHCO).13C NMR (75.47 MHz, DMSO-d 6): δ = 20.9, 25.1, 25.6, 28.3, 33.4, 33.8, 47.0, 59.1, 61.2, 122.4, 122.6, 127.5, 134.3, 137.1, 157.9, 169.9. Anal. Calcd for C18H24N6O: C, 63.51; H, 7.11; N, 24.69. Found: C, 63.41; H, 7.02; N, 24.60. 4-(1-Cyclohexyl-1H-tetrazol-5-yl)-4-methyl-8-nitro-4,5-dihydro-1H-benzo[b][1,4]diazepin-2(3H)-one (9c) Red powder; mp 233–234 °C. IR (KBr): 3347, 3295, 3200, 3139, 3087, 2926, 2851, 1675, 1634, 1597, 1526, 1449, 1376 cm–1. 1H NMR (300.13 MHz, DMSO-d 6): δ = 1.00–1.80 (13 H, m, 5 CH2 of cyclohexyl and CH3), 3.12 (2 H, m, CH2), 4.71 (1 H, m, CH of cyclohexyl), 7.04 (1 H, s, NH), 7.70 (1 H, s, HAr), 7.84 (2 H, m, HAr), 10.00 (1 H, br s, NHCO). 13C NMR (75.47 MHz, DMSO-d 6): δ = 23.4, 24.7, 25.1, 29.8, 32.9, 33.9, 46.2, 58.2, 63.2, 115.3, 117.9, 120.5, 123.2, 134.3, 148.0, 158.4, 167.4. Anal. Calcd for C17H21N7O3: C, 54.98; H, 5.70; N, 26.40. Found: C, 54.90; H, 5.60; N, 26.35. 4-(1-tert-Butyl-1H-tetrazol-5-yl)-4-methyl-4,5-dihydro-1H-benzo[b][1,4]diazepin-2(3H)-one (9d) Colorless crystals; mp 246–247 °C. IR (KBr): 3348, 3289, 3196, 3128, 3075, 2970, 2917, 2870, 1674, 1648, 1600, 1523, 1467, 1374 cm–1. 1H NMR (300.13 MHz, DMSO-d 6): δ = 1.70 (9 H, m, 3 CH3), 1.80 (3 H, s, CH3), 2.61 (1 H, ABq, J = 13.6 Hz, CH2), 3.21 (1 H, ABq, J = 13.9 Hz, CH2), 6.03 (1 H, br s, NH), 6.70–7.10 (4 H, m, HAr), 9.57 (1 H, br s, NHCO). 13C NMR (75.47 MHz, DMSO-d 6): δ = 31.0, 32.8, 49.0, 63.1, 64.3, 121.0, 121.6, 122.6, 125.2, 127.5, 131.2, 160.0, 170.1. Anal. Calcd for C15H20N6O: C, 59.98; H, 6.71; N, 27.98. Found: C, 59.88; H, 6.65; N, 27.99. 4-Methyl-4-[1-(2,4,4-trimethylpentan-2-yl)-1H-tetrazol-5-yl]-4,5-dihydro-1H-benzo[b][1,4]diazepin-2(3H)-one (9e) White crystals; mp 263–265 °C. IR (KBr): 3357, 3310, 3196, 3075, 2962, 2891, 2860, 1672, 1603, 1507, 1393, 1319 cm–1. 1H NMR (300.13 MHz, DMSO-d 6): δ = 1.70 (12 H, br s, 4 CH3), 2.25 (2 H, s, CH2), 2.64 (8 H, s, 2 CH3 and CH2), 5.73 (1 H, s, NH), 6.70–7.20 (4 H, m, HAr), 9.70 (1 H, br s, NHCO). 13C NMR (75.47 MHz, DMSO-d 6): δ = 28.1, 30.8, 31.6, 43.6, 45.8, 53.6, 63.0, 67.6, 121.9, 123.3, 125.1, 126.2, 128.9, 130.6, 161.9, 167.2. Anal. Calcd for C19H28N6O: C, 64.02; H, 7.92; N, 23.58. Found: C, 64.05; H, 7.85; N, 23.55. 4-(1-Benzyl-1H-tetrazol-5-yl)-4-methyl-4,5-dihydro-1H-benzo[b][1,4]diazepin-2(3H)-one (9f) Yellow powder; mp 192–194 °C. IR (KBr): 3354, 3285, 3212, 3028, 2965, 2854, 1681, 1635, 1517, 1450, 1374 cm–1. 1H NMR (300.13 MHz, DMSO-d 6): δ = 1.75 (3 H, br s, CH3), 2.91 (2 H, br s, CH2), 5.69 (1 H, ABq, J = 15.3 Hz, CH2), 6.01 (1 H, ABq, J = 15.3 Hz, CH2), 6.88 (1 H, m, NH), 7.00–7.45 (9 H, m, HAr), 8.70 (1 H, br s, NHCO). 4.30 (2 H, m, CH2), 5.13 (1 H, br s, NH), 6.66 (1 H, d, J = 7.95 Hz, HAr), 6.76 (2 H, m, HAr), 7.27 (5 H, m, HAr), 8.45 (1 H, m, NHCO), 9.47 (1 H, br s, NHCO). 13C NMR (75.47 MHz, DMSO-d 6): δ = 28.9, 46.5, 52.3, 62.0, 121.8, 122.4, 125.5, 128.0, 128.5, 128.6, 129.1, 130.5, 135.6, 137.4, 159.0, 170.1. Anal. Calcd for C18H18N6O: C, 64.66; H, 5.43; N, 25.13. Found: C, 64.60; H, 5.33; N, 25.10. 4-Methyl-4-[1-(2-methylbenzyl)-1H-tetrazol-5-yl]-4,5-dihydro-1H-benzo[b][1,4]diazepin-2(3H)-one (9g) Yellow powder; mp 192–194 °C. IR (KBr): 3354, 3285, 3212, 3028, 2965, 2854, 1681, 1635, 1517, 1450, 1374 cm–1. 1H NMR (300.13 MHz, DMSO-d 6): δ = 1.75 (3 H, s, CH3), 1.85 (3 H, s, CH3), 2.73 (2 H, br s, CH2), 6.44 (1 H, m, NH), 6.80–7.00 (4 H, m, HAr), 7.20–7.40 (4 H, m, HAr), 9.79 (1 H, br s, NHCO). 13C NMR (75.47 MHz, DMSO-d 6): δ = 23.0, 29.8, 46.1, 58.9, 61.5, 121.9, 122.1, 122.4, 125.4, 126.9, 127.5, 128.5, 128.9, 129.0, 129.4, 137.6, 139.9, 158.6, 169.6. Anal. Calcd for C19H20N6O: C, 65.50; H, 5.79; N, 24.12. Found: C, 65.50; H, 5.79; N, 24.12. 4-(1-tert-Butyl-1H-tetrazol-5-yl)-4-methyl-8-nitro-4,5-dihydro-1H-benzo[b][1,4]diazepin-2(3H)-one (9h) Red powder; mp 237–239 °C. IR (KBr): 3348, 3289, 3196, 3128, 3075, 2970, 2917, 2870, 1674, 1648, 1600, 1523, 1467, 1374 cm–1. 1H NMR (300.13 MHz, DMSO-d 6): δ = 1.82 (9 H, m, 3 CH3), 2.31 (3 H, br s, CH3), 3.19 (2 H, s, CH2), 4.37 (1 H, br s, NH), 7.65 (2 H, s, HAr), 8.47 (1 H, s, HAr), 9.13 (1 H, br s, NHCO). 13C NMR (75.47 MHz, DMSO-d 6): δ = 30.7, 31.3, 44.8, 63.8, 64.8, 121.9, 123.9, 124.1, 126.2, 130.5, 148.5, 159.4, 170.4. Anal. Calcd for C15H19N7O3: C, 52.17; H, 5.55; N, 28.39. Found: C, 52.11; H, 5.48; N, 28.30.