Asymmetric oganocatalytic Friedel-Crafts hydroxyalkylation of indoles using electrophilic pyrazole-4,5-diones

The electrophilic reactivity of a series of novel pyrazole-4,5-dione derivatives in the organocatalytic Friedel-Crafts reaction with various substituted indoles has been tested. The disclosed procedure catalyzed by a cinchona alkaloid derivative allows the conjugation of two very important aza-heterocyclic scaffolds to generate a new class of indolylpyrazolones bearing a tetrasubstituted stereocenter in excellent yields (up to 99%) and with enantioselectivities of up to 94:6 er. © Georg Thieme Verlag Stuttgart. New York