The regioselective chemistry of alkoxyxenon fluoride

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Xenon difluoride reacts with methanol to form the unstable reactive species methoxyxenon fluoride ( 1 ). In the absence of unsaturated hydrocarbons, this specie quantitatively disproportionates to formaldehyde and hydrogen fluoride; however, in the presence of alkene substrates a competitive methoxyfluorination reaction results. During methoxyfluorination, the highly reactive intermediate ( 1 ) displays a novel ambivalent addition character depending upon whether catalysis is accomplished by protonic acids (H 2SO 4 & HF generated in-situ ) or Lewis acid species (BF 3 & BF 3 etherate). Catalysis with protonic acids produces an apparent fluorine electrophilic intermediate ( 2 ) where fluorine adds first and results in Markownikoff fluoromethoxy products predominating. Reaction in the presence of Lewis acids provides a positive oxygen electrophile as intermediate ( 3 ) where the methoxy group adds first and produces ▪ mainly anti -Markownikoff fluoromethoxy products. The reaction mechanism involving species 1 , 2 , and 3 were studied by using five alkenes with varying structural features; in the case of the very electron rich alkene dihydropyran, reaction with XeF 2 occurred before 1 could form. Current mechanistic studies of this alkoxyfluorination reaction involve varying the alcoholic substrate with electron-donating and electron-withdrawing alkoxy moieties.