Transition-Metal-Free TBAI-Facilitated Addition–Cyclization of N-Methyl-N-arylacrylamides with Arylaldehydes or Benzenesulfonohydrazides: Access to Carbonyl- and Sulfone-Containing N-Methyloxindoles

A highly efficient addition–cyclization of N-methyl-N-arylacrylamides with arylaldehydes or benzenesulfonohydrazides was developed using a catalytic amount of the quaternary ammonium salt (TBAI) under metal-free conditions, leading to the carbonyl- and sulfone-containing oxindoles. Compared to previous methods, which require excessive amounts of explosive organic peroxides and precious or toxic metal reagents, the present protocol, which gave access to 3,3-disubstituted oxindoles, is a safe and green approach, resulting in the formation of various useful carbonyl- and sulfone-containing oxindoles in yields of 40–94%.