Rhodium(III)-Catalyzed Annulation between N-Sulfinyl Ketoimines and Activated Olefins: C–H Activation Assisted by an Oxidizing N–S Bond

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• 作者：Qiang Wang ; Yingzi Li ; Zisong Qi ; Fang Xie ; Yu Lan ; Xingwei Li
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：March 4, 2016
• 年：2016
• 卷：6
• 期：3
• 页码：1971-1980
• 全文大小：755K
• ISSN：2155-5435

文摘

C–H activation under redox-neutral conditions, especially by Rh(III) catalysis, has offered attractive synthetic strategies. Previous work in redox-neutral C–H activation relied heavily on the cleavage of oxidizing N–O and N–N directing groups, and cleavable N–S bonds have been rarely used, although they may offer complementary coupling patterns. In this work, N-sulfinyl ketoimines were designed as a novel substrate for the redox-neutral coupling with different activated olefins via a Rh-catalyzed C–H activation pathway. The coupling with acrylate esters afforded 1H-isoindoles with the formation of three chemical bonds around a quaternary carbon. Furthermore, the coupling with maleimides furnished pyrrolidone-fused isoquinolines. A broad scope of substrates has been established. The mechanism of the coupling with acrylates has been studied in detail by a combination of experimental and computational methods. This coupling proceeds via imine-assisted C–H activation of the arene followed by ortho C–H olefination to afford a Rh(III) olefin hydride intermediate which, upon deprotonation, may exist in equilibrium with a Rh(I) olefin species. Cleavage of the N–S bond occurs only after C–H olefination to generate a Rh(III) imide species. DFT studies indicated that the imide group can undergo migratory insertion to produce a Rh(III) secondary alkyl which isomerizes under the assistance of acetic acid to a Rh(III) tertiary alkyl that is prone to insertion of the second acrylate.