Synthesis of novel 2,3-dihydro-8H-thieno[2,3-d]azepines and 1,2,3,4-tetrahydro-1H-3-benzazepines via photolyses of 6-azido-2,3-dihydrobenzo[b]thiophene and 6-azido-1,2,3,4-tetrahydronaphthalene

Abstract

Reduction of 6-amino-2,3-dihydrobenzo[b]thiophene 1,1-dioxide with DIBAL-H gave 6-amino-2,3dihydrobenzo[b]thiophene which was converted by standard procedures into 6-azido-2,3dihydrobenzo[b]thiophene (7). Photolyses of this azide in an excess of diethylamine gave 7-diethylamino-2,3-dihydro-8H-thieno[2,3-d]azepine (10) whose structure was confirmed by ¹H n.m.r. spectroscopic studies and by conversion through successive bromination and elimination of hydrogen bromide from the intermediate into 7-diethylamino-8H-thieno[2,3-d] azepine (13), which was shown to be different from 6-diethylamino-8H-thieno[2,3-c]azepine (12), prepared by debromination of its 2,3-dibromo derivative (11). By contrast with the behaviour of azide (7), irradiation of 6-azido-1,2,3,4-tetrahydronaphthalene (14) in THF containing diethylamine or morpholine gave a mixture of the two possible azepines, (17) and (19) or (18) and (20), respectively, with (19) and (20) being the major isomers.