palladium-formate reducing system to give stereoselective formation of functionalized 1,2,4-trisubstituted-1,3-dienes in good to high yield. With arylethynyl,dialkylcarbinols this reaction provides a convenient entry into conjugateddienes containing an oxygem atom at the allylic position. The nature of the base (Et3N, n-Bu3N, NaHCO3) and the temperature affect the regiochemical outcome of the reaction. A high degree