Enantioselective Organocatalytic Construction of Spiroindane Derivatives by Intramolecular Friedel-Crafts-Type 1,4-Addition

The highly enantioselective organocatalytic construction of spiroindanes containing an all-carbon quaternary stereocenter by intramolecular Friedel-Crafts-type 1,4-addition is described. The reaction was catalyzed by a cinchonidine-based primary amine and accelerated by water and p-bromophenol. A variety of spiro compounds containing quaternary stereocenters were obtained with excellent enantioselectivity (up to 95 % ee). The reaction was applied to the asymmetric formal synthesis of the spirocyclic natural products (-)-cannabispirenones A and B. Art and crafts: Intramolecular Friedel-Crafts-type 1,4-addition under organocatalytic conditions enabled the highly enantioselective construction of spiroindanes containing an all-carbon quaternary stereocenter. The reaction was applied to the asymmetric formal synthesis of the spirocyclic natural products (-)-cannabispirenone A and B (see scheme).