1, 2-Disubstituted olefins undergo the vinylic substituilon reaction with triarylphosphine- palladium acetate catalysts, stereospecifically via a syn addition of the organopalladium intermediate followed by a syn “palladium hydride” elimination. 2 In the absence of a triarylphosphine, aryl iodides, but not bromides, reacted also, but with considerable loss of atereochemistry, presumably because of multiple palladi um hydride readdition- ...