An efficient route to 2,6-disubstituted styrenes via the palladium-catalyzed [4+2] cyclodimerization of conjugated enynes

An efficient and general method for the synthesis of 2,6-disubstituted styrenes 5 via the palladium-catalyzed [4+2] homobenzannulation of conjugated enynes 4 was developed. In all cases, the reactions proceeded in regiospecific manner, affording the disubstituted styrenes, bearing various functional groups at the 2 and 6 positions of the benzene ring, as a single reaction product in good to excellent yields. Initial attempts at cross-cycloaddition of two different enynes indicated low degrees of chemoselectivity of this process. Accordingly, the cross-dimerization products 6 in all cases were accompanied with notable amounts of the chemoisomeric homodimers 5.