Tantalum pentachloride-catalyzed reactions of alkynes with Et3Al

Tantalum pentachloride-catalyzed reaction of 1,2-dialkyl-acetylenes with Et₃Al affords regio- and stereoselectively tetraalkyl-substituted (Z,E)-hexa-1,3-dienes and (Z)-tri-substituted olefins in a ratio of 2 : 1. In cases of 1-alkynylphosphines, 1-alkynylsilanes and 2-alkynylamines, the corresponding functionalized monoolefins are formed.