Photoinduced Proton Transfer Reactions for Mild O-H Functionalization Reactions of Unreactive Alcohols

Hexafluoroisopropanol is typically considered as an unreactive solvent and not as a reagent in organic synthesis. Herein, we report on a mild and efficient photochemical reaction of aryl diazoacetates with hexafluoroisopropanol that enables, under stoichiometric reaction conditions, the synthesis of fluorinated ethers in excellent yield. We support these findings with mechanistic studies, which indicate a preorganization of hexafluoroisopropanol and the diazoalkane as an unreactive Lewis Acid-Base adduct. Only upon photoexcitation, this adduct undergoes a protonation-substitution reaction to the reaction product. We conclude with investigations on the applicability of this photochemical transformation and could show that a broad variety of acidic alcohols can be subjected to this transformation and thus demonstrate the feasibility of this concept in O-H functionalization reactions (52 examples, up to 98% yield).