Synthesis of thieno[2,3-c]- and thieno[3,2-c]-azepinones

Abstract

The 7-benzyl-5,6,7,8-tetrahydro-4H-thieno[2,3-c]azepin-4-one (11) has been synthesized from the N-benzyl-N-(2-thenyl)-β-alanine (10) by a tin(IV) chloride-catalysed Friedel-Crafts cyclization. In addition, N-benzyl- and N-(p-tolylsulphonyl)-N-(3-thenyl)-β-alanine (16a) and (16b) cyclized more effectively to give 5-benzyl- and 5-(p-tolylsulphonyl)-4,5,6,7-tetrahydro-8H-thieno[3,2-c]azepin-8-one (17a) and (17b), respectively. Attempts to remove the p-tolylsulphonyl group from compound (17b) was achieved by use of polyphosphoric acid (PPA) and afforded the 4,5,6,7-tetrahydro-8H-thieno[3,2-c]azepin-8-one (19). In contrast, 7-bromo-5-(p-tolylsulphonyl)-4,5,6,7-tetrahydro-8H-thieno-[3,2-c]azepin-8-one (20) gave the novel heterocyclic system, 6,7-dihydroazirino[1,2-a]-thieno[2,3-d]pyridin-8-one (22) under similar conditions.