Studies in 1-Aza-1,3-butadienes: Diels-Alder Cyclo-Addition Reaction of 1-Aza-1,3-butadienes with Ketene Leading to the Synthesis of δ-Lactams

Abstract

Snyder et at⁽¹⁾ have reported the formation of Diels-Alder type adduct from the reaction of N-2-ethylhexene-2-ylidene-aniline and maleic anhydride which then cyclised to the corresponding product, 5,7-diethyl-2-phenyl-2-aza-bicyclo[2,3,1]oct-6-ene-3-one-8- carboxylic acid. Demoulin et at⁽²⁾ have recently reported that 1-dimethylamino-2-azabutadienes react with electrophilic acetylenic and olefinic dienophiles with loss of dimethylamine to give pyridines or dihydropyridines. Layer⁽³⁾ has pointed out that cinnamylidene aniline does not undergo 1,4-cycloaddition since it has no ε-hydrogen atom which must tautomerise, if the reaction is to succeed as the reaction involved the enamine and not the imine. Extensive studies have been carried out on the addition of ketenes⁽⁴⁾ to carbon-nitrogen double bonds to yield β -lactams. Recently, a cycloaddition of a substituted ketene with conjugeted imines has been reported⁽⁵⁾. But the reaction of these imines with ketene obtained under Reformatsky reaction conditions has not been reported so far. Therefore, the cycloaddition of 1-aza- 1, 3-butadienes with ketene obtained from α -bromoethyl acetate and zinc dust has been carried out, 1-Aza-1, 3-butadienes were obtained by reacting equimolar amounts of cinnamaldehyde⁽³⁾ and aromatic amines either in ethyl alcohol or in benzene using a Dean and Stark water separtor.