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-vinylcyclobu- tanols, 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 catal- ysis. In the presence of a catalytic amount of Pd(OAc)2- (PPh3)2, AgTFA and triflic acid, the reaction of 1 or 2 with aryl iodides affords 2,3,4-trisubstituted dihydrofur- ans, 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 trans- position of allylic alcohol and ring opening of the azetidine/oxetane by an internal hydroxyl group.