Palladium-Catalyzed Regioselective Cyclopropanating Allenylation of (2,3-Butadienyl)malonates with Propargylic Carbonates and Their Application to Synthesize Cyclopentenones

An efficient and highly regioselective route to synthesize polysubstituted 1,3,4-alkatrien-2-yl cyclopropane derivatives via Pd(0)-catalyzed highly regioselective coupling cyclization of (2,3-butadienyl)malonate or bis(phenylsulfonyl)methane with propargylic carbonates was reported. The reaction proceeded smoothly under neutral conditions to afford the products in 73-96% yields. The products may be efficiently converted to cyclopentenone derivatives via a catalytic Pauson-Khand reaction under ambient conditions.