Tandem imino-pinacol coupling-aza-Michael reaction promoted by Zn/InCl3: a novel multicomponent strategy for diastereoselective synthesis of monocyclic 1,4-diazepine in water

Aldimine formed in situ on bimolecular reductive coupling in the presence of zinc and accelerated by indium(III) chloride in water afforded N,N'-diphenyl-1,2-diaryl-1,2-diamino ethane which on aza-Michael addition with alpha,beta-unsaturated ketone and subsequent dehydrative cycloaddition yielded monocyclic 1,4-diazepine in excellent yield and with high diastereoselectivity in one-pot. The whole reaction sequence proceeded smoothly with quantitative conversion of reactants into product. The reaction pathway was supported by isolation of N,N'-diphenyl-1,2-diaryl-1,2-diamino ethane and its conversion into product by reaction with alpha,beta-unsaturated ketone under similar reaction conditions.