Chemoselective Intermolecular Cross-Benzoin Reaction of Aliphatic Aldehydes and Isatins via N-Heterocyclic Carbene Catalysis

Abstract

An N-heterocyclic carbene (NHC)-catalyzed chemoselective intermolecular cross-benzoin reaction of aliphatic aldehydes with isatins is developed, affording biologically important 3-substituted 3-hydroxyoxindoles (on gram scale) in moderate to good yields (46–90%). The employment of a morpholinone-derived pentafluorophenyl-substituted triazolium salt as the electron-deficient NHC pre-catalyst is essential to make the reaction go through the cross-benzoin reaction pathway rather than the hydroacylation reaction pathway.