Direct Aroylation of Olefins through a Cobalt/Photoredox‐Catalyzed Decarboxylative and Dehydrogenative Coupling with α‐Oxo Acids

Abstract

A photoredox/cobalt dual catalytic procedure has been developed that allows benzoylation of olefins. Here the photoredox catalyst effects the decarboxylation of α-ketoacids to form benzoyl radicals. After addition of this radical to styrenes, the cobalt catalyst abstracts a H-atom. Hydrogen evolution from the putative cobalt hydride intermediate allows a Heck-like aroylation without the need for a stoichiometric oxidant. Mechanistic studies reveal that electronically different styrenes lead to a curved Hammett plot, thus suggesting a change in product-determining step in the catalytic mechanism.

Strategies and Mechanisms of First-Row Transition Metal-Regulated Radical C–H Functionalization

“…The Tunge group also developed a cobaloxime/photoredox-catalyzed method for the C(sp 2 )−H aroylation of olefins using α-oxo acids as acyl radical precursors in 2022. 369 In 2020, Dong's group reported a HAT reaction between alkyl radicals and [Co(II)] complexes as an approach to C(sp 2 )−H arylation and employed this technique for the cobaloximecatalyzed dehydrogenative cyclization of o-teraryls (45-26) (Scheme 45d). 370 The simple model compound 1,4-dihydronaphthalene was used to investigate the role of light and the Co catalyst in this process.…”

Single-Step Synthesis of γ-Ketoacids through a Photoredox-Catalyzed Dual Decarboxylative Coupling of α-Oxo Acids and Maleic Anhydrides

“…The commercially available phenylglyoxylic acid 1a and phenyl maleic anhydride 2a were selected as model substrates for exploring this transformation. The determined optimal reaction conditions were based on our previously reported successful system, with minor adaptations that included lowering the photocatalyst loading to 2.5 mol % ( PC1 - Mes-Acr-Ph + BF 4 ) and employing dimethylaminopyridine (DMAP) as the substoichiometric base for inducing the initial decarboxylation. Adding sufficient water as a cosolvent was also necessary for aiding hydrolysis (see Supporting Information for extensive optimization results).…”

“…A common observation in these photocatalytic decarboxylative protocols is that alkyl oxo acids generally provide lower product yields than the analogous aryl acids. The acyl radical formed in these cases have been observed to undergo decarbonylation to the subsequent carbon centered radical . Similarly, when the thioester derivative of an α-oxo-acid was used, this subsequent decarbonylation was observed, yielding the sulfide 3n as a product of thiophenoxy radical addition.…”