Concise synthesis of (S,S)-(+)-Dehydrohomoancepsenolide

[GRAPHICS] A concise total synthesis of the bis-butenolide 3 in optically active form is reported. Key steps are a zinc mediated "three component coupling" with formation of dienyne 9 which undergoes ring closing metathesis (RCM) on treatment with (PCy3)(2)Cl2Ru=CHPh. Dimerization of the resulting butenolide 11 is then achieved via alkyne metathesis using (tBuO)(3)W=CCMe3 as the catalyst. A Lindlar reduction completes this synthesis which delivers product 3 in only five steps with an overall yield of 25%.