Selective demethylation of O-aryl glycosides by iridium-catalyzed hydrosilylation

Abstract

The cleavage of alkyl ethers by hydrosilylation is a powerful synthetic tool for the generation of silyl ethers. Previous attempts to apply this transformation to carbohydrate derivatives have been constrained...

Light-Promoted Transfer of an Iridium Hydride in Alkyl Ether Cleavage

“…This proposal is inspired by work on related systems that operate without light, [33][34][35][36][37]43,44 as well as the reported photochemical behavior of the bipyridine-supported iridium hydride reported by Miller. 24 Complex 2 likely reacts with NaBAr F 4 and triethylsilane to form the electrophilic σ-silane complex 4 that has been previously characterized by Djukic and co-workers under relevant alcohol dehydrosilylation conditions.…”

“…Complex 1 is a reported catalyst for the dehydrosilylation of alcohols using triethylsilane in the absence of light . The proposed mechanism for this transformation involves the intermediacy of a cationic σ-silane complex that undergoes heterolytic Si–H cleavage followed by bimolecular reaction of the resulting hydride and oxonium ions in a second step. , A closely related mechanism is operative in hydrosilylative ether cleavage, a transformation with only a few reported catalysts comprised of either electron-deficient boranes , or cationic iridium complexes. − In the absence of light, 1 is a very poor catalyst for alkyl ether reduction, which we postulated might be due to the modest nucleophilicity of the hydride intermediate. Under blue-light irradiation, however, 1 catalyzes the hydrosilylative demethylation of trans -4-( tert -butyl)­cyclohexyl methyl ether to the corresponding silyl ether in 43% yield (Table , entry 2).…”