Nickel-Catalyzed Reductive Benzylation of Aldehydes with Benzyl Halides and Pseudohalides

Photocatalytic Decarboxylative Coupling of Arylacetic Acids with Aromatic Aldehydes

An efficient protocol was proposed for the preparation of secondary alcohols in good to excellent yields via photoredox-catalyzed decarboxylative couplings between readily available arylacetic acids and a variety of less reactive (hetero)aromatic aldehydes. The formation of carbanion is the key intermediate in this reaction. Various substituted arylacetic acids and aldehydes were all compatible with this transformation under mild reaction conditions. Furthermore, the current protocol was successfully applied to the direct alcoholization of several drug acids.

Silyl-mediated photoredox-catalyzed radical–radical cross-coupling reaction of alkyl bromides and ketoesters

A strategy for cross-coupling between organic bromides and carbonyl compounds is developed by combining photocatalysis and halogen atom transfer using a photocatalyst and tris(trimethylsilyl)silane.

Catalytic Aldehyde and Alcohol Arylation Reactions Facilitated by a 1,5-Diaza-3,7-diphosphacyclooctane Ligand

We report a catalytic method to access secondary alcohols by the coupling of aryl iodides. Either aldehydes or alcohols can be used as reaction partners, making the transformation reductive or redox-neutral, respectively. The reaction is mediated by a Ni catalyst and a 1,5-diaza-3,7-diphosphacyclooctane. This P₂N₂ ligand, which has previously been unrecognized in cross-coupling and related reactions, was found to avoid deleterious aryl halide reduction pathways that dominate with more traditional phosphines and NHCs. An interrupted carbonyl-Heck type mechanism is proposed to be operative, with a key 1,2-insertion step forging the new C-C bond and forming a nickel alkoxide that may be turned over by an alcohol reductant. The same catalyst was also found to enable synthesis of ketone products from either aldehydes or alcohols, demonstrating control over the oxidation state of both the starting materials and products.

Nickel-Catalyzed Cross-Coupling of Alkyl Carboxylic Acid Derivatives with Pyridinium Salts via C-N Bond Cleavage

The electrophile-electrophile cross-coupling of carboxylic acid derivatives and alkylpyridinium salts via C-N bond cleavage is developed. The method is distinguished by its simplicity and steers us through a variety of functionalized ketones in good to excellent yields. Besides acid chlorides, carboxylic acids were also employed as acylating agents, which enabled us to incorporate acid-sensitive functional groups such as MOM, BOC, and acetal. Control experiments with TEMPO revealed a radical pathway.

Deoxygenative cross-electrophile coupling of benzyl chloroformates with aryl iodides

This work describes Ni-catalyzed cross-electrophile coupling of benzyl chloroformate derivatives with aryl iodides that generates a wide range of diaryl methane products. The mild reaction conditions merit the C-O bond radical fragmentation of benzyl chloroformates via halide abstraction or a single electron reduction by a Ni catalyst. This work offers a new substrate type for cross-electrophile couplings.

Visible-Light-Driven External-Reductant-Free Cross-Electrophile Couplings of Tetraalkyl Ammonium Salts

Cross-electrophile couplings between two electrophiles are powerful and economic methods to generate C-C bonds in the presence of stoichiometric external reductants. Herein, we report a novel strategy to realize the first external-reductant-free cross-electrophile coupling via visible-light photoredox catalysis. A variety of tetraalkyl ammonium salts, bearing primary, secondary, and tertiary C-N bonds, undergo selective couplings with aldehydes/ketone and CO₂. Notably, the in situ generated byproduct, trimethylamine, is efficiently utilized as the electron donor. Moreover, this protocol exhibits mild reaction conditions, low catalyst loading, broad substrate scope, good functional group tolerance, and facile scalability. Mechanistic studies indicate that benzyl radicals and anions might be generated as the key intermediates via photocatalysis, providing a new direction for cross-electrophile couplings.

Nickel-Catalyzed Reductive Etherification of Aldehydes at Room Temperature: C-O vs C-C Bond Formation

The reaction of secondary and tertiary benzyl alcohols activated by 2,4,6-trichloro-1,3,5-triazine (TCT) with aldehydes in the presence of NiCl₂·dmg as a precatalyst in ethylene glycol afforded ethers at room temperature. A selective C-O vs C-C bond formation was observed for the secondary and tertiary benzyl alcohols in comparison with primary ones.

Direct Synthesis of Secondary Benzylic Alcohols Enabled by Photoredox/Ni Dual-Catalyzed Cross-Coupling

An operationally simple, mild, redox-neutral method for the cross-coupling of α-hydroxyalkyltrifluoroborates is reported. Utilizing an Ir photocatalyst, α-hydroxyalkyl radicals are generated from the single-electron oxidation of the trifluoroborates, and these radicals are subsequently engaged in a nickel-catalyzed C-C bond-forming reaction with aryl halides. The process is highly selective, functional group tolerant, and step economical, which allows the direct synthesis of secondary benzylic alcohol motifs.