NHC-CDI Betaine Adducts and Their Cationic Derivatives as Catalyst Precursors for Dichloromethane Valorization.

Zwitterionic adducts of N-heterocyclic carbene and carbodiimide (NHC-CDI) are an emerging class of organic compounds with promising properties for applications in various fields. Herein, we report the use of the ICyCDI(-Tol) betaine adduct () and its cationic derivatives and as catalyst precursors for the dichloromethane valorization via transformation into high added value products CHZ (Z = OR, SR or NR). This process implies selective chloride substitution of dichloromethane by a range of nucleophiles NaZ (preformed or generated from HZ and an inorganic base) to yield formaldehyde-derived acetals, dithioacetals, or aminals with full selectivity. The reactions are conducted in a multigram-scale under very mild conditions, using dichloromethane both as a reagent and solvent, and very low catalyst loading (0.01 mol %). The CHZ derivatives were isolated in quantitative yields after filtration and evaporation, which facilitates recycling the dichloromethane excess. Mechanistic studies for the synthesis of methylal CH(OMe) rule out organocatalysis as being responsible for the CH transfer, and a phase-transfer catalysis mechanism is proposed instead. Furthermore, we observed that and react with NaOMe to form unusual isoureate ethers, which are the actual phase-transfer catalysts, with a strong preference for sodium over other alkali metal nucleophiles.