Unlocking the 5‐ exo Pathway with the Au I ‐Catalyzed Alkoxycyclization of 1,3‐Dien‐5‐ynes

Abstract

The first general regio‐ and stereoselective 5‐exo gold(I)‐catalyzed alkoxycyclization of a specific class of 1,5‐enynes such as 1,3‐dien‐5‐ynes has been described, despite 1,5‐enynes being known to almost invariably proceed via endo cyclizations under gold‐catalysis. The configuration of the terminal alkene in the starting 1,3‐dien‐5‐yne plays a crucial role on the regiochemical outcome of the reaction. A wide variety of interesting alkoxy‐functionalized alkylidenecyclopentenes have been synthesized from 1‐monosubstituted (E)‐1,3‐dien‐5‐ynes. On the contrary, the corresponding Z isomers evolve affording formal 6‐endo cyclization products. In addition, mechanistic exploration supports a highly stabilized carbocation as a key intermediate instead of a highly constrained cyclopropyl gold carbene from E isomers, and also accounts for the well differentiated reactivity observed between both E/Z geometrical isomers as well as for the stereochemical outcome of the reaction.