Enantioselective Silylation of Simple Alcohols by Catalyst-Controlled Dehydrogenative Si-O Coupling

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Non-enzymatic kinetic resolution (KR) of alcohols through silylation rapidly established itself as an alternative to the common acylation in the last ten years. Substoichiometric amounts of chiral imidazole-type bases together with chlorosilanes enabled the KR and the related desymmetrization of a broad range of 1,2- and 1,3-diol motifs. Attempts to resolve monools, i.e., simple secondary or even tertiary alcohols, have only been met with limited success so far. The field was recently further advanced by the identification of chiral Brønsted acids as catalysts, and one of them, for the first time, allowed for the KR of unfunctionalized alcohols using hexamethyldisilazane as silylation reagent. Our approach to stereoselective alcohol silylation is based on transition-metal-catalyzed silicon-oxygen coupling of alcohols and hydrosilanes, liberating dihydrogen as the sole waste. Both reagent- and catalyst-controlled KRs were developed by us a few years ago but high selectivity factors were only achieved with donor-functionalized and as such biased alcohols. After considerable experimentation, we found a powerful catalyst/hydrosilane combination that mediates the dehydrogenative coupling between simple alcohol and commercially available hydrosilanes with high efficiency. The project aims at putting this new method on a sound basis, including broad substrate scope and extension to desymmetrization reactions.