The alkoxyl radical is an important reactive intermediate in mechanistic studies and organic synthesis; however, its current generation from alcohol oxidation heavily relies on transition metal activation under strong oxidative conditions. Here we report the first visible-light-induced alcohol oxidation to generate alkoxyl radicals by cyclic iodine(III) reagent catalysis under mild reaction conditions. The β-fragmentation of alkoxyl radicals enables selective C(sp(3))-C(sp(3)) bond cleavage and alkynylation/alkenylation reactions with various strained cycloalkanols, and for the first time with linear alcohols.
Chemoselective C(sp(3))-C(sp(2)) coupling reactions under mild reaction conditions are useful for synthesizing alkyl-substituted alkenes having sensitive functional groups. Reported here is a visible-light-induced chemoselective alkenylation through a deboronation/decarboxylation sequence under neutral aqueous reaction conditions at room temperature. This reaction represents the first hypervalent-iodine-enabled radical decarboxylative alkenylation reaction, and a novel benziodoxole-vinyl carboxylic acid reaction intermediate was isolated. This C(sp(3))-C(sp(2)) coupling reaction leads to aryl-and acyl-substituted alkenes containing various sensitive functional groups. The excellent chemoselectivity, stable reactants, and neutral aqueous reaction conditions of the reaction suggest future biomolecule applications.
Inert chemical bond cleavage and functionalization reactions provide expedient synthetic routes and are fundamental in organic synthesis. Alkoxyl radicals enable inert chemical bond cleavages by hydrogen atom transfer and β-fragmentation reactivity; however their further synthetic transformations and functional group compatibility are limited by traditional alkoxyl radical generation methods. Recently, visible-light-induced alkoxyl radical generation methods have emerged and led to new advancements in inert chemical bond cleavage reactions and subsequent functionalization, with excellent chemoselectivity and functional group compatibility. In this Feature Article, the generation of alkoxyl radicals by different visible-light-induced methods and their common or distinct reactivity are discussed, which are categorized by C(sp3)-H, C(sp3)-C(sp3), and C(sp3)-X bond cleavages and subsequent transformations.
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