Electrochemical Arene Radical Cation Promoted Spirocyclization of Biaryl Ynones: Access to Alkoxylated Spiro[5,5]trienones.

Herein, a novel electrochemical arene radical cation promoted dearomative spirocyclization of biaryl ynones with alcohols is described, providing a conceptually novel transformation mode for producing diverse alkoxylated spiro[5,5]trienones. The catalyst- and chemical-oxidant-free spirocyclization protocol features broad substrate scope and high functional group tolerance. Mechanistic studies reveal that the generation of arene radical cation via anodic single-electron oxidation is crucial, with sequential 6-endo-dig cyclization, dissociation of hemiketal, anodic oxidation, and nucleophilic attack of alcohols.

Electroreductive Carboxylation of Propargylic Acetates with CO2: Access to Tetrasubstituted 2,3-Allenoates.

An electroreductive carboxylation of propargylic alcohols with CO2 and then workup with TMSCHN2 to construct tetrasubstituted 2,3-allenoates is developed. This method allows the incorporation of an external ester group into the resulting allene system through electroreduction, carboxylation, and deacetoxylation cascades. Mechanistically, electricity on/off experiments and cyclic voltammetry analysis support the preferential generation of the CO2 radical anion or the 3-aryl propargylic acetate radical anion based on the electron nature of the aryl rings.

Nickel Photocatalyzed Reductive 1,4-Dicarbofunctionalization of 1,3-Enynes with N-Methylamines and Organohalides Enabled by Site-Selective C(sp3)-H Functionalization.

A cooperative nickel and photoredox reductive catalysis for 1,4-dicarbofunctionalization of 1,3-enynes with tertiary N-methylamines and organohalides to produce tetrasubstituted allenes is presented. This method enables the generation of the aminoalkyl C(sp3)-centered radicals by site selective cleavage of the N-methyl C(sp3)-H bonds in tertiary N-methylamines and is extended to alkyl bromides as the electrophilic terminating regents. Mechanistic studies indicate that the reaction involves a radical process and a Ni0/NiI/NiIII catalytic cycle.

Nickel-Catalyzed Arylcarbamoylation of Alkenes of N-(o-Iodoaryl)acrylamides with Nitroarenes via Reductive Aminocarbonylation: Facile Synthesis of Carbamoyl-Substituted Oxindoles.

Nickel-catalyzed arylcarbamoylation reactions of alkenes of N-(o-haloaryl)acrylamides with CO and nitroarenes via reductive aminocarbonylation to produce carbamoyl-substituted oxindoles with an all-carbon quaternary stereogenic center are presented. Starting with N-(o-haloaryl)acrylamides, simple CO, and inexpensive nitroarenes and using a Ni catalyst, a dinitrogen-based ligand, a Zn reductant, a TMSCl additive, and a base system, this protocol enables the synthesis of various carbamoyl-substituted oxindoles and allows the efficient late-stage derivatization of valuable molecules.

Synthesis of N-arylsulfonamides via Fe-promoted reaction of sulfonyl halides with nitroarenes in an aqueous medium.

A fascinating Fe-promoted protocol for the synthesis of N-arylsulfonamides has been developed. Starting from commercially available nitroarenes and sulfonyl chlorides, moderate to excellent yields of the corresponding N-arylsulfonamides can be obtained. In particular, Fe dust serves as the sole reductant in the transformation and it can be easily performed on a large scale.