Synthesis of 1,2-Dihydrobenz[c]azepin-3-one via Acid-catalyzed Cyclization of N-Arylmethyl-N-methyl-3-phenylsulfanylacrylamide

Treatment of N-arylmethyl-N-methyl-cis-3-phenylsulfanyl acrylamide (5) with p-toluenesulfonic acid induced two reactions; cyclization to 1,2-dihydrobenz[c]azepin-3-ones (7) and N-dearylmethylation to N-methylacrylamides (9 and 10) depending on the structures of the substrates. The route provides a simple method of preparing 6-methoxy- (7e), 8-methoxy- (7d), 6,8-dimethoxy- (7f), and 8,9-dimethoxy-N-methyl-1,2-dihydrobenz-[c]azepin-3-ones (7g), although the scope is limited by some side reactions.