Reactions of enaminones with diazocarbonyl compounds

The [Cu(acac)₂]-catalyzed reactions of several tertiary enaminones with three diazocarbonyl compounds, i.e., dimethyl diazomalonate, ethyl diazoacetoacetate, and ethyl diazoacetate, yielded amino- and additionally carbonyl-substituted dihydrofurans, together with further furan derivatives. Due to the conjugation of α-carbonyl/α-Ph groups, reactions proceeded only via 1,5-electrocyclization of corresponding keto-ylides. On the other hand, in the absence of any α-substituent, tertiary enaminone and ethyl diazoacetate, reacted via an accompanying mechanism by a push-pull cyclopropane intermediate, to yield a 2,4-dicarbonyl-substituted furan in one step with moderate yield.