Palladium−Iminophosphine-Catalyzed Alkynylstannylation of Alkynes

A palladium complex coordinated by an iminophosphine ligand was found to catalyze the addition of alkynylstannanes to a carbon−carbon triple bond of various alkynes in moderate to good yields with exclusive syn selectivity. The alkynyl group in the stannanes was attached mainly to the internal carbon of terminal alkynes, except for 1-alkyn-3-ones and alkynoates, where the alkynyl group was connected to the terminal carbon. Steric bulk of the ligand markedly influenced on the regioselectivity and reaction rate: an iminophosphine with a bulkier imino moiety accelerated the alkynylstannylation with higher regioselectivity. On the basis of these observations, the mechanism of the present reaction is discussed.