Electrohydrogenative Coupling of Thioamides with Olefins by Cobalt Catalysis

Abstract

Catalytic reduction of unsaturated substrates provides a powerful tool for bulk and fine chemical synthesis. However, very few examples have been reported on the reductive transformation of thioamides, presumably because of the poisoning of catalysts by sulfur-containing molecules. Herein, we describe an efficient and sustainable hydrogenative coupling of thioamides with olefins under electrocatalytic conditions. The key to success for this reductive process is the application of an earth-abundant cobalt complex as the cost-effective and robust molecular electrocatalyst. As only protons (H⁺) and electrons (e^–) as the hydrogen source and redox equivalent, this polarity-reversed electrochemical protocol is showcased by highly selective and straightforward synthesis of a wide range of α-branched amines, as well as deuterium isotope labeling applications. Over 60 α-branched amines, including 12 deuterated analogues, have been successfully synthesized. Notably, a variety of functional groups, including aryl halides, esters, and nitriles, are well tolerated under the mild electrochemical conditions. Furthermore, late-stage modification of complex molecules has also been achieved. Mechanistic studies indicate that the in-situ generated imines and α-amino radicals by cobalt-electrocatalytic desulfurization of thioamides are identified as the key intermediates in this transformation. This work provides an alternative and versatile method for the synthesis of structurally diverse α-branched amines, with advantages including sustainability, high selectivity, and compatibility with isotope labeling and complex molecular functionalization.

Keywords

Cobalt hydride catalysis / Electrosynthesis / Deuteration / Hydrogenative coupling / Thioamides / Olefin / α-Amino radical / Desulfurization

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