Enantioselective synthesis of benzylbutyrolactones from 5-hydroxyfuran-2(5H )-one. New chiral synthons for dibenzylbutyrolactone lignans by a chemoenzymatic route

A chemoenzymatic method is described for the asymmetric synthesis of benzylbutyrolactones. (R)-5-Acetoxyfuran-2(5H)-one (12) was obtained with ee > 99% in a multigram scale catalytic esterification using immobilized lipase PS. The addition of lithiated dithianes to chiral synthon 12 was followed by an effective multistep reduction to produce enantiomerically pure benzylbutyrolactones.