Catalytic Synthesis of Nonracemic Azaproline Derivatives by Cyclization of β‐Alkynyl Hydrazines under Kinetic Resolution Conditions

Abstract

No metals required : Starting from readily accessible γ‐silyl allenyl esters, β‐alkynyl hydrazines were prepared in one step and subsequently cyclized in the presence of ammonium and phosphonium catalysts leading to dehydroazaproline products (see scheme; X=O, S). These heterocycles were also produced in high enantiomeric excesses using chiral ammonium phase‐transfer catalysts by a kinetic resolution.