A Stereoselective Entry into Functionalized 1,2-Diamines by Zinc-Mediated Homologation of α-Aminoacids

A general, stereoselective synthesis of 4,5-disubstituted imidazolidines-2-ones from α-aminoacids has been developed: the key steps are a Blaise reaction of bromoacetate on α-aminonitriles and further reduction. Although reduction with sodium cyanoborohydride afforded a mixture of cis and trans isomers 6a−e with moderate to good stereoselectivity, reduction with sodium in liquid ammonia gave the trans isomers 8a−e with complete stereoselectivity. Acidic hydrolysis of the urea gave 4-amino-pyrrolidinones, which can be precursors to β,γ-diaminoacids or 3-aminopyrrolidines.