Advances in free-radical alkylation and arylation with organoboronic acids

Photoredox-Catalyzed Radical Hydroalkylation of Azobenzenes with Alkylboronic Acids

The facile synthesis of N-alkyl-N,N'-diarylhydrazines has been a long-standing challenge. Here, we report a photoredox-catalyzed hydroalkylation of azobenzenes with alkylboronic acids, which successfully affords diverse N-alkyl-N,N'-diarylhydrazines. With an acridinium salt as the photocatalyst and upon visible light irradiation, a broad range of azobenzenes and alkylboronic acids reacted smoothly in the presence of a Lewis base at ambient temperature. Mechanistic studies revealed that the reaction proceeds via the generation of alkyl radicals and is facilitated by photoredox catalysis.

Synthesis of Polysubstituted Aromatics via the Pd(II)-Initiated Borono-Catellani Reaction

Herein, we report a novel palladium(II)-initiated borono-Catellani reaction that utilizes widely accessible aryl boronic acids that serve as both the reaction-initiating and -terminating substrates for the first time. The borono-Catellani reaction was facilitated by cooperative catalysis between Pd(OAc)2 and NBE, with air serving as the oxidizing agent, opening new venues for developing novel Catellani-type reactions. Importantly, this method is compatible with a wide range of substrates, including naphthaleneboronic acid, phenylboric acid derivatives, alkyl iodides, and aryl iodides, under these environmentally friendly and mild reaction conditions, thereby demonstrating versatile functional group compatibility for the synthesis of valuable polysubstituted aromatics.

Copper-Catalyzed 1,4-Alkylarylation of 1,3-Enynes with Ethers and Aryl Boronic Acids Enabled via C(sp3)-H Functionalization

Herein, we present a copper-catalyzed, three-component intermolecular 1,4-alkylarylation of 1,3-enynes with ethers and aryl boronic acids. This method, driven by α-C(sp3)-H functionalization of the oxygen atom in ethers, regioselectively produces various tetrasubstituted allenes from simple, readily available precursors. Key features include mild reaction conditions and a simple catalytic system.

Ethynyl-B(dan) in [3+2] Cycloaddition and Larock Indole Synthesis: Synthesis of Stable Boron-Containing Heteroaromatic Compounds

The cycloaddition of nitrile oxides with ethynyl-B(dan) (dan=naphthalene-1,8-diaminato) allowed the facile preparation of diverse isoxazolyl-B(dan) compounds, all of which displayed excellent protodeborylation-resistant properties. The dan-installation on the boron center proves vital to the high stability of the products as well as the perfect regioselectivity arising from hydrogen bond-directed orientation in the cycloaddition. The diminished boron-Lewis acidity of ethynyl-B(dan) also renders it amenable to azide-alkyne cycloaddition, Larock indole synthesis and related heteroannulations. The obtained boron-containing triazole, indoles, benzofuran and indenone exhibit sufficient resistance toward protodeborylation. Despite the commonly accepted transmetalation-inactive property derived from the diminished Lewis acidity, the synthesized heteroaryl-B(dan) compound was still found to be convertible to the oligoarene via sequential Suzuki-Miyaura coupling.