Platinum and Ruthenium Chloride-Catalyzed Cycloisomerization of1-Alkyl-2-ethynylbenzenes: Interception of x-Activated Alkynes with aBenzylic C-H Bond

摘要

Air-stable and commercially available alkynophilic metal salts, such as PtCl_2, PtCl_4, and [RuCl_2(CO)_3]_catalyze the cycloisomerization of 1-alkyl-2-ethynylbenzenes to produce substituted indenes even atan ambient temperature. Electrophilically activated alkynes can be intercepted by simple benzylicC-H bonds at primary, secondary, and tertiary carbon centers. Mechanistic studies, such as labelingstudies and kinetic isotope and substituent effects, indicate that the cycloisomerization proceedsthrough the formation of a vinylidene intermediate and turnover-limiting 1,5-shift of benzylichydrogen.