Enantioselective reductive coupling of 1,3-enynes to glyoxalates mediated by hydrogen: Asymmetric synthesis of β,γ-unsaturated α-hydroxy esters

Catalytic hydrogenation of 1,3-enynes 1a-8a in the presence of ethyl glyoxalate at ambient pressure and temperature using a rhodium catalyst modified by (R)-(3,5- ^tBu-4-MeOPh)-MeO-BIPHEP results in highly regio- and enantioselective reductive coupling to furnish the corresponding a-hydroxy esters 1b-8b. As demonstrated by the elaboration of a-hydroxy ester 1b, the terminal and internal olefin moieties embodied by the diene side chain are subject to selective manipulation, one over the other.