Enantioselective Direct Reductive Coupling of Conjugated Alkynes and α-Ketoesters

Significance

This report utilizes hydrogen to mediate the reductive coupling of conjugated alkynes with α-ketoesters. High enantioselectivity is obtained with (R)-xylyl-WALPHOS (1) as the chiral ligand. Interestingly, the authors found that aging of the dichloroethane solvent gave increased yields and selectivity. This could be explained by the increase in Brønsted acid concentration. The reaction was optimized by addition of 2 mol% of triphenylacetic acid. Various conjugated enynes were utilized giving an array of products with high optical purity. Single geometric isomers are obtained and no reduction of either alkene portion was seen.