Asymmetric 1,4-additions to 5-alkoxy-2(5h)-furanones

The synthesis of enantiomerically pure 5-menthyloxy-2(5H)-furanones is described as well as the diastereoselective 1,4-addition of thiols to these butenolides to yield new homochiral C4-synthons. Kinetic resolution of 5-methoxy-2(5H)-furanone, with an enantiomeric excess of 13%, was achieved by cinchonidine catalyzed thiophenol addition. The synthetic utility of the asymmetric thiol additions is illustrated in an efficient route to enantiomerically pure (R)- and (S)-3,4-epoxy-1-butanol.