Investigation of the interaction of a NHC-CDI zwitterion with ZnCl2 in dichloromethane led to the serendipitous discovery of a highly selective, double C–Cl activation of dichloromethane.

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( p -Tol) betaine adduct ( 1a ) and its cationic derivatives 2a and 3a as catalyst precursors for the dichloromethane valorization via transformation into high added value products CH 2 Z 2 (Z = OR, SR or NR 2 ). This process implies selective chloride substitution of dichloromethane by a range of nucleophiles Na + Z – (preformed or generated in situ 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 CH 2 Z 2 derivatives were isolated in quantitative yields after filtration and evaporation, which facilitates recycling the dichloromethane excess. Mechanistic studies for the synthesis of methylal CH 2 (OMe) 2 rule out organocatalysis as being responsible for the CH 2 transfer, and a phase-transfer catalysis mechanism is proposed instead. Furthermore, we observed that 1a and 2a 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.

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