Organocatalytic Enantioselective Synthesis of Chiral Spiro-indoline-pyrazolones through a formal [4+1] Annulation Reaction of 4-Bromopyrazolones and aza-ortho-Quinone Methides

Abstract

In this communication, a straighforward asymmetric synthesis of spiro-indoline-pyrazolone compounds is described. This methodology consists in a formal [4+1] cycloaddition reaction of 4-bromopyrazolones and aza-ortho-quinone methides generated in situ catalyzed by a bisquinine-derived squaramide in CHCl₃ under basic conditions. A variety of chiral spirocyclic compounds bearing a pyrazolone and an indoline moieties were obtained in moderate to good yields (up to 68 %) and moderate to excellent enantioselectivities (up to 93 % ee).