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Open AccessArticle

[2+2+2] Annulation of N-(1-Naphthyl)acetamide with Two Alkynoates via Cleavage of Adjacent C–H and C–N Bonds Catalyzed by an Electron-Deficient Rhodium(III) Complex

Department of Chemical Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8550, Japan
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Academic Editor: Michal Szostak
Molecules 2018, 23(12), 3325; https://doi.org/10.3390/molecules23123325
Received: 21 November 2018 / Revised: 7 December 2018 / Accepted: 12 December 2018 / Published: 14 December 2018
(This article belongs to the Special Issue Amide Bond Activation)
It has been established that an electron-deficient cationic CpE-rhodium(III) complex catalyzes the non-oxidative [2+2+2] annulation of N-(1-naphthyl)acetamide with two alkynoates via cleavage of the adjacent C–H and C–N bonds to give densely substituted phenanthrenes under mild conditions (at 40 °C under air). In this reaction, a dearomatized spiro compound was isolated, which may support the formation of a cationic spiro rhodacycle intermediate in the catalytic cycle. The use of N-(1-naphthyl)acetamide in place of acetanilide switched the reaction pathway from the oxidative [2+2+2] annulation-lactamization via C–H/C–H cleavage to the non-oxidative [2+2+2] annulation via C–H/C–N cleavage. This chemoselectivity switch may arise from stabilization of the carbocation in the above cationic spiro rhodacycle by the neighboring phenyl and acetylamino groups, resulting in the nucleophilic C–C bond formation followed by β-nitrogen elimination. View Full-Text
Keywords: alkynes; C–H bond cleavage; C–N bond cleavage; cyclopentadienyl complexes; N-(1-naphthyl)acetamide; rhodium; [2+2+2] annulation alkynes; C–H bond cleavage; C–N bond cleavage; cyclopentadienyl complexes; N-(1-naphthyl)acetamide; rhodium; [2+2+2] annulation
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Terasawa, J.; Shibata, Y.; Fukui, M.; Tanaka, K. [2+2+2] Annulation of N-(1-Naphthyl)acetamide with Two Alkynoates via Cleavage of Adjacent C–H and C–N Bonds Catalyzed by an Electron-Deficient Rhodium(III) Complex. Molecules 2018, 23, 3325.

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