We describe the development of gold-and platinum-catalyzed cycloisomerizations of 1, 5- enynes. This catalytic process displays a wide alkyne scope and furnishes a range of highly functionalized 1, 4-and 1, 3-cyclohexadienes. In the case of 1-siloxy-1-yne-5-enes, the reactions are efficiently catalyzed by AuCl (1 mol%) at ambient temperature to afford siloxy cyclohexadienes or the corresponding 1, 2-and 1, 3-cyclohexenones upon subsequent ...