Synthesis of polysubstituted furans by palladium-catalyzed coupling of butatrienyl carbinols with aryl halides and triflates

An efficient one-pot two-step synthesis of polysubstituted furans is described using readily available 4,5-epoxy-2-alkynyl esters as starting materials. In the first step, reduction of these with SmI2 affords buta-1,2,3-trienyl carbinol intermediates which, in the second step, participate in Pd(0)-catalyzed cyclization reactions with aryl halides and triflates by a mechanism probably involving oxidative addition, intramolecular oxypalladation and reductive elimination steps. In this manner, up to four carbon substituents are incorporated onto the furan ring, with the aryl group being introduced at the furan 3- or 4-positions. These features make the method particularly suitable for regioselective synthesis of tetrasubstituted furans.