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.