Reactivity of chiral α-amidoalkylphenyl sulfones with stabilized carbanions.: Stereoselective synthesis of optically active 1-aminopyrrolizidine

Metal enolates and functionalized allylzinc reagents react with optically active alpha-amidoalkylphenyl sulfones to give N-carbamoylamino derivatives with variable levels of anti diastereoselectivity. Zinc enolates provide comparable results with respect to lithium enolates in terms of diastereoselectivity but afford beta-amino ester derivatives in lower yield. The synthetic utility of the obtained chiral N-carbamoylamino esters is demonstrated by the first enantioselective synthesis of (-)-1-aminopyrrolizidine a central intermediate for the preparation of various biologically active substances.