The arylative oxygenation of the electron-rich olefins styrene, α-methylstyrene, vinyl pyrrolidinone, and vinyl oxazolidinone was accomplished using arenediazonium salts and catalytic amounts of FeSO4 in an effective single electron transfer radical process. A broad range of aryldiazonium salts was tolerated using water, methanol, or their combination with acetonitrile to furnish the corresponding carbohydroxylated and carbomethoxylated products (42 examples), including functionalized dihydroisocoumarin and dihydrobenzofuran systems in good to excellent yields (up to 88%). The protocols developed for the Fe(II)-catalyzed carbohydroxylation were also compared to Ru(II) and Ir(III) photoredox carbooxygenations of these electron-rich olefins. The Fe(II)-catalyzed process proved to be highly competitive compared to the photoredox and the uncatalyzed processes. The proposed mechanism for the Fe(II)-catalyzed reactions involves the synergic combination with an effective Fe+2/Fe+3 redox system and a radical polar crossover mechanism featuring an unprecedented capture of the reactive N-acyliminium in the case of vinyl pyrrolidinone and vinyl oxazolidinone.

This review provides an overview of the use of aryldiazonium salts as the source of aryl radicals and their application in the development of selective transformations over the last 13 years. Examples were organized under thermal and photocatalytic transformations. This review provides an accessible follow‐up in this field for both radical and catalytic chemists working in industry as well as academia.

A new enantioselective intramolecular strategy for the synthesis of enantioenriched bridged benzoxacines, unsaturated spirobenzofurans, 2,3‐dihydrobenzofuran and 2,3‐indoline acetate scaffolds in a tandem‐like diazotization/Heck‐Matsuda process directly from anilines has been developed. The process combines the in situ diazotization of the aniline, followed by the intramolecular Heck‐Matsuda reaction, thus skipping the isolation and purification of potentially unstable or hard‐to‐synthesize aryldiazonium salts. The practicality and robustness of the sequence were demonstrated by the synthesis of 30 complex motifs in yields up to 91% and enantiomeric ratios up to 97:3, including quaternary stereocenters. The in‐tandem processes from anilines were compared to conventional Heck‐Matsuda reactions using pre‐synthesized aryldiazonium salts. With few exceptions, the reactions starting directly from the anilines afforded better overall yields and enantioselectivity, demonstrating the efficiency of the method.

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A new enantioselective intramolecular strategy for the synthesis of enantioenriched bridged benzoxacines, unsaturated spirobenzofurans, methyl-2,3-dihydrobenzofuran acetates, and methyl-2,3-indoline acetate scaffolds in a tandem-like diazotization/Heck Matsuda process directly from anilines has been developed. The process combines the in situ diazotization of the aniline, followed by the intramolecular Heck-Matsuda reaction, thus skipping the isolation and purification of unstable or hard-to-synthesize aryldiazonium salts. The practicality and robustness of the sequence were demonstrated by the synthesis of 26 examples of complex structural motifs with yields up to 91% and enantiomeric ratio (er) up to 97:3, including quaternary stereocenters. The in-tandem processes from anilines were compared to conventional Heck Matsuda reactions using pre-synthesized aryldiazonium salts. With few exceptions, the reactions starting directly from the anilines afforded better overall yields and er, demonstrating the efficiency of this method.