Arylative Ring Expansion of 3-Vinylazetidin-3-Ols and 3-Vinyloxetan-3-Ols to Dihydrofurans by Dual Palladium and Acid Catalysis.

In contrast to the well-studied 1-vinylcyclobutanols, the reactivity of 3-vinylazetidin-3-ols 1 and 3-vinyloxetan-3-ols 2 under transition metal catalysis remains largely unexplored. We report herein their unique reactivity under dual palladium and acid catalysis. In the presence of a catalytic amount of Pd(OAc) 2 (PPh 3 ) 2 , AgTFA and triflic acid, the reaction of 1 or 2 with aryl iodides affords 2,3,4-trisubstituted dihydrofurans, which are valuable heterocycles in organic synthesis. Mechanistic studies reveal that this arylative ring-expansion reaction proceeds via a domino process involving Heck arylation of alkene, acid-catalyzed transposition of allylic alcohol and ring opening of the azetidine/oxetane by an internal hydroxyl group.