An enyne metathesis/(4+2)-dimerization route to (+/-)-differolide

[GRAPHICS] A concise total synthesis of (+/-)-differolide (1) has been achieved. 2-Vin ylbutenolide (2) was prepared by enyne metathesis of allyl propynoate (3) u sing the Grubbs initiator 4, This reaction was examined by H-1 NMR spectros copy, which led to the hypothesis that low concentration of ruthenium speci es and high concentration of enyne substrate would be advantageous. Accordi ngly, slow addition of 4 to solutions of enyne 3 was found to be beneficial . Spontaneous dimerization of 2 gave (+/-) differolide (1) and an isomer.