NHC Precursor Catalyzed C3-Chloromethylation of Oxindole with Dichloromethane as C1 Synthon.

The construction of sterically hindered all-carbon α-chloromethyl quaternary centers remains a major synthetic challenge due to both steric congestion and limited efficient methods. Herein, we report a mild and efficient protocol for the chloromethylation of oxindoles using dichloromethane (DCM) as a C1 synthon, mediated by an NHC precursor. This reaction proceeded under mild conditions with broad substrate scope, high chemoselectivity, and good to excellent yields across over 30 examples. Preliminary mechanistic studies suggested a unique pathway distinct from that of conventional NHC catalysis. The method demonstrated excellent scalability and offered a versatile and green approach to access α-chloromethyl quaternary centers, providing valuable intermediates for further transformations in pharmaceutical and organic synthesis.