Dimerization-carbostannylation of alkynes catalyzes by a palladium-diiminecomplex: Regioselectivity, stereoselectivity and mechanism

Double insertion of alkynes into the C-Sn bond of an alkynyl-, alkenyl-, al lyl- or arylstannane proceeded in the presence of a palladium-diimine compl ex to afford highly conjugated alkenylstannanes with exclusive syn selectiv ity. Perfect regioselectivities were observed in the dimerization-carbostan nylation of ethyl propiolate with a palladium-1.2-bis[(2,6-diisopropylpheny l)imino]acenaphthene complex. which allowed regio- and stereoselective synt hesis of stannyl-substituted muconic acid derivatives. The pi -conjugation of the dimerization-carbostannylation products was further extended through a cross-coupling or homocoupling reaction. A palladacyclopentadiene is pro posed as an intermediate species.