Tandem pseudopericyclic processes in the cyclization of α-diazonitriles to 5-halo-1,2,3-triazoles. Scope and limitations

Issue in Honor of Prof. Albert Padwa ARKIVOC 2002 (viii) 166-179 General procedure for preparation of adducts 2, 4 of diazonitrile with HHal A 4.54 N solution of HHal in dry diethyl ether (4 mL) was added to the solution of 1 mmol diazo compound 1 in 50 mL dry diethyl ether at 0oC. The precipitate was filtered, washed with 50 mL dry ether and dried at 0oC under reduced pressure. 5-Halo-1,2,3-triazoles 3, 5, 6a–l. General procedure A solution of 1 mmol diazoacetonitrile 1 in 20 mL CHCl3 was added to 20 mL CHCl3 saturated with HHal. The reaction mixture was stirred for 10 h at 400C. The solvent was removed under reduced pressure, the product crystallized from ethanol, and dried. Table 3. The adducts 2, and 4 diazo compound and HHal Comp. Yield (%) IR (KBr), cm-1 C=O CN CN2 Find, % Hal Hal- Calc., % Hal Formula 2a 98 1690 2235 2155 38.7 38.7 38.8 C3H4Cl2N4O 2b 95 1685 2220 2150 36.3 36.2 36.0 C4H6Cl2N4O 2c 98 1680 2220 2160 26.6 26.5 26.7 C9H10Cl2N4O 2d 99 1675 2225 2153 27.4 27.3 27.4 C9H2Cl2N4O 4a 96 1700 2255 2157 58.8 58.8 58.8 C3H4Br2N4O 4b 98 1664 2231 2146 56.0 56.0 55.9 C4H6Br2N4O 4c 99 1660 2225 2150 45.1 44.9 45.1 C9H10Br2N4O 4d 98 1665 2220 2140 45.8 45.3 45.9 C9H2Br2N4O 4e 97 1645 2220 2145 42.4 42.4 42.3 C10H10Br2N4O2 4f 99 1668 2215 2135 44.1 44.1 44.1 C10H10Br2N4O 4g 99 1670 2230 2140 56.3 37.9 56.2 C9H7Br3N4O 4h 98 1670 2220 2150 53.1 53.0 53.1 C5H7Br2N3O2 4i 87 1645 2220 2135 59.1 58.7 59.0 C4H5Br2N3O 4j 89 1648 2220 2115 48.1 47.8 48.0 C9H7Br2N3O 4k 92 1640 2220 2135 44.1 44.0 44.0 C10H9Br2N3O2 4l 96 1650 2220 2130 46.2 46.2 46.1 C10H9Br2N4O 4m 98 1670 2230 2120 49.3 49.1 49.2 C4H2Br2F3N3O 4n 90 1685 2210 2115 41.5 41.4 41.6 C12H8Br2N4O 5-Chloro-1,2,3-triazole-4-carboxamide (3a). Yield 87%, white crystals, m.p. 192–4oC. IR, 3485 (NH), 1685 (C=O) cm-1. UV, .max, nm, (log e): 231 (3.81). Found: C, 24.7; H, 1.9; Cl, 24.2; N, 38.6. C3H3ClN4O requires C, 24.6; H, 2.1; Cl, 24.2; N, 38.2%. N-Methyl-5-chloro-1,2,3-triazole-4-carboxamide (3b). Yield 91%, white crystals, m.p. 192– 3oC. IR, 3390 (NH), 1640 (C=O) cm-1. UV, .max, nm, (log e): 207 (3.84), 237 (3.91). 1H NMR 8.82 (1H, br s, NH), 2.86 (3H, d, Me). Found: C, 92.8; H, 3.0; Cl, 21.9; N, 34.9. C3H5ClN4O requires: C, 29.9; H, 3.1; Cl, 22.1; N, 34.9%. ISSN 1424-6376 Page 175 ©ARKAT USA, Inc