Aryl Radical Activation of C–O Bonds: Copper-Catalyzed Deoxygenative Difluoromethylation of Alcohols
2021
Cai, Aijie | Yan, Wenhao | Liu, Wei
Given their ubiquity in natural products and pharmaceuticals, alcohols represent one of the most attractive starting materials for the construction of C–C bonds. We report herein the first catalytic strategy to harness the reactivity of aryl radicals for the activation of C–O bonds in alcohol-derived xanthate esters, allowing for the discovery of the first catalytic deoxygenative difluoromethylation reaction. Under copper-catalyzed conditions, a wide variety of alkyl xanthate esters, readily synthesized from alcohol feedstocks, were activated by catalytically generated aryl radicals and were converted to the alkyl-difluoromethane products via alkyl radical intermediates. This scalable protocol exhibits a broad substrate scope and functional group tolerance, enabling late-stage modification of complex pharmaceutical agents. A one-pot protocol has been developed that allows for the direct use of free alcohols without purification of the xanthate esters. Mechanistic studies are consistent with the hypothesis of aryl radicals being formed and initiating the cleavage of the C–O bonds of xanthate esters, to generate alkyl radicals as the key intermediates. This aryl radical activation approach represents a new strategy for the activation of alcohols as cross-coupling partners.
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