Double insertion of alkynes into the C–Sn bond of an alkynyl-, alkenyl-, allyl- or arylstannane proceeded in the presence of a palladium–diimine complex to afford highlyconjugatedalkenylstannanes with exclusive syn selectivity. Perfect regioselectivities were observed in the dimerization–carbostannylation of ethyl propiolate with a palladium–1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene complex