Diethyl bromodifluoromethylphosphonate: a highly efficient and environmentally benign difluorocarbene precursor

A convenient method for the difluoromethylation of phenols and thiophenols, using diethyl bromodifluoromethylphosphonate (1) as a difluorocarbene precursor, is described. This commercially available phosphonate was found to undergo an extremely facile P-C bond cleavage on basic hydrolysis (−78 °C to rt), presumably leading to the bromodifluoromethyl anion, which subsequently converts to a difluorocarbene intermediate. The latter is trapped by phenolates 2 or thiophenolates 3 to give the corresponding difluoromethyl ethers and thioethers in good to excellent yield. The resulting eco-friendly side product, diethyl phosphate ion, is easily separated from the reaction mixture due to its excellent solubility in water. Due to the mild conditions applied to this reaction, phenolate ions bearing carbonyl or enolate functions are selectively difluoromethylated.

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