Electrochemical Arylation of Aldehydes, Ketones, and Alcohols: from Cathodic Reduction to Convergent Paired Electrolysis.

Arylation of carbonyls, one of the most common approaches toward alcohols, has received tremendous attention, as alcohols are important feedstocks and building blocks in organic synthesis. Despite great progress, there is still a great gap to develop an ideal arylation method featuring mild conditions, good functional group tolerance, and readily available starting materials. We now show that electrochemical arylation can fill the gap. By taking advantage of synthetic electrochemistry, commercially available aldehydes (ketones) and benzylic alcohols can be readily arylated to provide a general and scalable access to structurally diverse alcohols (97 examples, >10 gram-scale). More importantly, convergent paired electrolysis, the ideal but challenging electrochemical technology, was employed to transform low-value alcohols into more useful alcohols. Detailed mechanism study suggests that two plausible pathways are involved in the redox neutral α-arylation of benzylic alcohols.

Electrochemical Synthesis of trans-2,3-Disubstituted Aziridines via Oxidative Dehydrogenative Intramolecular C(sp3)-H Amination.

An electrochemical oxidative dehydrogenative C(sp3)-H amination reaction to construct trans-2,3-disubstituted aziridines is reported, which avoids using external oxidants and generates only hydrogen gas as the byproduct. With KI as the mediator and electrolyte, the desired aziridines were prepared in good yields in an undivided cell at room temperature. The potential value of this mild electrochemical strategy was further highlighted by the gram-scale synthesis.

Organic Photoredox-Catalyzed Synthesis of δ-Fluoromethylated Alcohols and Amines via 1,5-Hydrogen-Transfer Radical Relay.

The hydrotrifluoromethylation of benzyl-protected homoallylic alcohol and amine derivatives catalyzed by 2,4,5,6-tetra(9 H-carbazol-9-yl)isophthalonitrile (4CzIPN) was developed. This reaction delivered δ-fluoromethylated free alcohols and amines with in situ deprotection of benzyl protecting group under mild irradiation conditions. 4CzIPN was found to be a competent metal-free photoredox catalyst for activating several types of fluoromethylation reagents including CF3SO2Cl, Togni's reagent, and 2-bromo-2,2-difluoroacetate via oxidative quenching and also CF3SO2Na through reductive quenching to allow direct hydrotrifluoromethylation of simple alkenes and Michael acceptors.

KO t Bu-promoted oxidative dimerizations of 2-methylquinolines to 2-alkenyl bisquinolines with molecular oxygen.

KO t Bu-promoted oxidative dimerizations of 2-methylquinolines with molecular oxygen as the oxidant have been developed for the first time. The mild reaction conditions allow the homo- and cross-dimerizations of 2-methylquinolines to give functionalized 2-alkenyl bisquinolines in highly trans-selective manners.