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

formula: see text] A concise total synthesis of (+/-)-differolide (1) has been achieved. 2-Vinylbutenolide (2) was prepared by enyne metathesis of allyl propynoate (3) using the Grubbs initiator 4. This reaction was examined by 1H NMR spectroscopy, which led to the hypothesis that low concentration of ruthenium species and high concentration of enyne substrate would be advantageous. Accordingly, slow addition of 4 to solutions of enyne 3 was found to be beneficial. Spontaneous dimerization of 2 gave (+/-)-differolide (1) and an isomer.