Enantioselective And Diastereodivergent Synthesis Of Spiroindolenines Via Chiral Phosphoric Acid-Catalyzed Cycloaddition

A diastereodivergent and enantioselective synthesis of chiral spirocyclohexyl-indolenines with four contiguous stereo-genic centers is achieved by a chiral phosphoric acid-catalyzed cycloaddition of 2-susbtituted 3-indolylmethanols with 1,3-dienecarbamates. Modular access to two different diastereoisomers with high enantioselectivities was obtained by careful choice of reaction conditions. Their functional group manipulation provides an efficient access to enantioenriched spirocyclohexyl-indolines and -oxindoles. The origins of this stereocontrol have been identified using DFT calculations, which reveal an unexpected mechanism compared to our previous work dealing with enecarbamates.