Direct Synthesis of Chiral Allenoates from the Asymmetric C-H Insertion of α-Diazoesters into Terminal Alkynes.

The asymmetric C-H insertion of α-diazoesters into 1-alkynes was achieved using chiral cationic guanidinium salts and copper(I) complexes. Optically active 2,4-disubstituted allenoates were generated under mild reaction conditions from various α-diazoesters and 1-alkynes in high yield (up to 99%) and enantioselectivity (up to 97:3 e.r.). Control experiments excluded the possibility of an asymmetric isomerization of alkynoates.