Sodium Borohydride Reduction of 1-Acyl-1,2(1H)-Diazepines and their Iron Tricarbonyl Complexes. Some Reactions of 2,3-Dihydro-1,2(1H)-Diazepines

Sodium borohydride reduction of the 1,2(lH)-diazepines 1a-e and 7, and the 1,2(1H)-diazepine iron tricarbonyl complexes 4a–b provides the 2,3-dihydro-1,2(1H)-diazepines 2a–e and 8, and the (2,3-dihydro-1,2(1H)-diazepine)Fe(CO)3 derivatives 5a–b, respectively. Fe(CO)3 complexes 5a and 6a may be also directly obtained from the 1,2(1H)-diazepines 2a and 3a, respectively. A number of diacylated compounds (3a–c, 6a–b, and 9) are prepared some of which (2a, 3a, 8, and 9) are readily converted into their corresponding (4 + 2)π cycloadducts (14a–d). Treatment of the borohydride reduction products 2a–c with sodium methoxide in methanol gives the 3,4-dihydro-1,2(2H)-diazepines 15a–c. Acetylation of 15a affords the 2-acetyl derivative 16a which may also be prepared by sodium methoxide deacetylation of either 3a or 9. 2-Tosyl-3,4-dihydro-1,2(2H)-diazepine (18) is obtained from 2a by a similar tosylation and deacetylation sequence. When either 2a or 3a are subjected to sodium methoxide in methanol-O-d, compounds 15a and 16a, respectively, are produced which show high deuterium incorporation at C4 and C6 (n.m.r. analysis). Photolysis of the 2,3-dihydro-1,2(1H)-diazepines 2a, 3a, 8, and 9 and the 3,4-dihydro-1,2(2H)-diazepine 16a affords the unstable 2,3-diazabicyclo[3.2.0]hept-6-ene 23a, 23b, 25a, and 25b and 1,2-diazabicyclo[3.2.0]hept-6-ene 27 derivatives, respectively. Treatment of either 25a or25b with sodium methoxide results cleanly in N2-deacylation to give compound 26.