Dual Cobalt and Photoredox Catalysis Enabled Intermolecular Oxidative Hydrofunctionalization

Abstract

A general protocol has been developed for the Markovnikov-selective intermolecular hydrofunctionalization based on visible-light-mediated Co/Ru dual catalysis. The key feature involves the photochemical oxidation of an organocobalt(III) intermediate derived from hydrogen atom transfer, which is supported by electrochemical analysis, quenching studies, and stoichiometric experiments. This redox process enables the efficient branch-selective alkylation of pharmaceutically important nucleophiles (phenols, sulfonamides, and various N-heterocycles) using a wide range of alkenes including moderately electrondeficient ones. Moreover, light-gated polar functionalization via organocobalt species was demonstrated.

Earth-Abundant 3d Transition Metal Catalysts for Hydroalkoxylation and Hydroamination of Unactivated Alkenes

“…In 2019, in order to widen the application scope of this cobalt-catalyzed alkene hydrofunctionalization methodology, the Zhu research group proposed to use an additional catalytic oxidant for a better redox matching during the radical-polar crossover process that converts the organocobalt(III) species (resulting from metal-hydride HAT of alkene followed by cage collapse) into the cationic organocobalt(IV) intermediates [96,97]. By evaluating the electrochemical properties of 4a-Co and its cyclohexenediamine-derivative as well as a model alkylcobalt(III)-salen complex, it was hypothesized that the facile reductive quenching of the excited state of Ru(bpy) 3+ by organocobalt(III) species should lead to the formation of the key Co(IV) intermediate and that subsequent nucleophilic trapping should give the desired Markovnikov product.…”

Photocatalysis in Dual Catalysis Systems for Carbon‐Nitrogen Bond Formation

“…More recently, Zhu and co‐workers reported another protocol for Markovnikov‐selective hydroamination by addition of N‐heterocycles to styrenes (Scheme 60). [80] …”

“…They reported the synthesis of an alkaloid clausine C by deacetylation of 404 (Scheme 71b) obtained by their standard procedure. Furthermore, Zhang, and most recently Zhu and co‐workers employed carbazoles for hydroamination of olefins [79,80] …”

Silane- and peroxide-free hydrogen atom transfer hydrogenation using ascorbic acid and cobalt-photoredox dual catalysis

“…We were motivated to devise silane-and peroxide-free catalytic HAT hydrogenation reactions in order to expand the scope of HAT hydrogenations beyond the canonical synthesis of complex molecules. We hypothesized that this might be possible by using ascorbic acid [38][39][40][41] and a combined cobalt/photoredox catalysis [42][43][44][45][46][47][48][49][50][51][52] (Fig. 1d).…”