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  • Title: Copper-Catalyzed Radical C-C Bond Cleavage and [4+1] Annulation Cascade of Cycloketone Oxime Esters with Enaminothiones.
    Author: He Y, Lou J, Wu K, Wang H, Yu Z.
    Journal: J Org Chem; 2019 Feb 15; 84(4):2178-2190. PubMed ID: 30632756.
    Abstract:
    Carbon-carbon bond formation is among the most important reactions in organic synthesis. Reconstruction of a carbon-carbon bond through ring-opening C-C bond cleavage of a strained carbocycle usually occurs via a thermodynamically preferable pathway. However, carbon-carbon bond formation through thermodynamically less favorable C-C bond cleavage has seldom been documented. Herein, we disclose an unusual C-C bond cleavage of cycloketone oxime esters for [4+1] annulation. Under anaerobic copper(I) catalysis, cycloketone oxime esters underwent regioselective, thermodynamically less favorable radical C-C bond cleavage followed by annulation with enaminothiones; that is, α-thioxo ketene N, S-acetals efficiently affording 2-cyanoalkyl-aminothiophene derivatives. Cyclobutanone, -pentanone, -hexanone, and -heptanone oxime esters could act as the effective C1 building blocks in the annulation reaction. An iminyl radical mechanism is proposed for the rare C-C bond cleavage/[4+1] annulation cascade.
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