Synthesis of Fluorinated Spiroindolenines by Transition Metal-Catalyzed Indole Dearomatizations

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A new strategy to access fluorinated spiroindolenines has been developed, involving a selective functionalization of indoles with fluorinated moieties and subsequent catalytic dearomatization. Trifluomethylthio (SCF3), diethyl phosphono(difluoromethyl)thio (SCF2P(O)(OEt)2) and (phenylsulfonyl)difluoromethyl (CF2SO2Ph) groups were successfully embedded at the C2 position of indole derivatives substituted with alkynes, allenes, and allyl carbonate moieties at the C3 position. A gold-catalyzed cycloisomerization gave access to six spiroindolenines, and an enantioselective palladium catalyzed cyclization provided 10 fluorinated spirocyclic products with up to 77% ee.