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 unique 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 electron-deficient ones. Moreover, light-gated polar functionalization via organocobalt species was demonstrated.

The Direct Decarboxylative N-Alkylation of Azoles, Sulfonamides, Ureas, and Carbamates with Carboxylic Acids via Photoredox Catalysis

“…It is worth noting that a single regioisomer was observed for imidazole 27 and indazoles 28 and 29a selectivity trend that is consistent with other reports where a nucleophilic displacement mechanism is proposed. 23 However, this regioselectivity is opposite to that obtained when copper catalysis is employed for N-alkylation via a reductive elimination mechanism, highlighting the complementarity of this decarboxylative protocol. 13 We attribute the observed regioselectivity for exclusive N 2 -alkylation to be due to formation of the kinetic product, which would be favored under our proposed S N 1-type reaction pathway.…”

Electrocatalytic Radical-Polar Crossover Hydroetherification of Alkenes with Phenols

“…This is mainly due to solvent cage escape process (k1) leading to the formation of solvent-separated radicals, which can irreversibly be driven to unwanted side reactions (Figure 1C, middle part). [43,[46][47] Thus, the development of a new catalytic strategy that allows proficient and controllable generation of highvalent cobalt(IV)-alkyl species or carbocations from the corresponding alkenes over solvent-cage escape process remains a major challenge for hydrofunctionalization with important but challenging nucleophiles such as phenols. [47][48][49] Herein we report a cobalt-catalyzed electrochemical radical polar crossover hydroetherification of alkenes in which a controllable electricity under HFIP co-solvent system drives systematic consecutive oxidations of cobalt catalyst to generate carbocationic species from a comprehensive class of olefins, which would subsequently be entrapped by phenols to afford the desired alkyl aryl ethers (Figure 1C, lower part).…”

“…[43,[46][47] Thus, the development of a new catalytic strategy that allows proficient and controllable generation of highvalent cobalt(IV)-alkyl species or carbocations from the corresponding alkenes over solvent-cage escape process remains a major challenge for hydrofunctionalization with important but challenging nucleophiles such as phenols. [47][48][49] Herein we report a cobalt-catalyzed electrochemical radical polar crossover hydroetherification of alkenes in which a controllable electricity under HFIP co-solvent system drives systematic consecutive oxidations of cobalt catalyst to generate carbocationic species from a comprehensive class of olefins, which would subsequently be entrapped by phenols to afford the desired alkyl aryl ethers (Figure 1C, lower part). We envisioned that the preferential use of alcoholic solvents such as HFIP would increase the microviscosity of the reaction system [46] , thereby eventually acquiring optimal chemoselectivity.…”

Cobalt Hydride Oxidase Catalysis Enabled Hydroamination of Unactivated Olefins

“…Second, oxidation of the resulting alkylcobalt(III) complex (B) by another molecule of Co(III)−X (X = anionic ligand or counterion) species (C) in the presence of an amine could lead to the amination product, presumably via an innersphere mechanism involving an organocobalt(IV) intermediate. 30,[32][33][34] The catalyst regeneration would involve aerobic oxidation of Co(II) species and a series of ligand transfers, which produces silanols as a benign byproduct. The underlying key is to eliminate free alkyl radicals in the reaction system, and isolate the dioxygen reduction from the oxidative functionalization process by invoking two distinct Co(III) species.…”

“…Next, electron transfer between 12 (Ep vs Fc + /Fc ~ −0.01 V) and a cationic Co(III) complex 10 (E1/2 vs Fc + /Fc = −0.02 V) would lead to a Co(II) complex 8 and a highly electrophilic organocobalt(IV) intermediate 13. 34 From 13, nucleophilic displacement at the α-carbon of the alkyl ligand would finally furnish the hydroamination product, meanwhile producing another molecule of 8.…”