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Co(III)-Catalyzed Coupling-Cyclization of Aryl C-H Bonds with alpha-Diazoketones Involving Wolff Rearrangement Xinwei Hu, Xun Chen, Youxiang Shao, Haisheng Xie, Yuanfu Deng, Zhuofeng Ke, Huanfeng Jiang, and Wei Zeng ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.7b03668 • Publication Date (Web): 16 Jan 2018 Downloaded from http://pubs.acs.org on January 16, 2018
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Table of Contents Graphic Co(III)-Catalyzed Coupling-Cyclization of Aryl C-H Bonds with Diazoketones Involving Wolff Rearrangement Xinwei Hu, Xun Chen, Youxiang Shao, Haisheng Xie, Yuanfu Deng, Zhuofeng Ke, Huanfeng Jiang, and Wei Zeng
R N Ar
N
R N
O
O +
H R = alkyl and aryl
Ar
CO2Et Co(III) cat. -N2
Ar
NO Co
•
R N Ar O
-NO
O
CO2Et Ar up to 86% yield 30+ examples Combination of cobalt-catalyzed Csp2-H activation/Wolff rearrangement Rapid access system for all-carbon quaternary center synthesis N2
Ar EtO2C
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Co(III)-Catalyzed Coupling-Cyclization of Aryl C-H Bonds with Diazoketones Involving Wolff Rearrangement Xinwei Hu,a,§ Xun Chen,a,c,§Youxiang Shao,b Haisheng Xie,a Yuanfu Deng,a Zhuofeng Ke,*,b Huanfeng Jiang,a and Wei Zeng*,a a
Key Laboratory of Functional Molecular Engineering of Guangdong Province, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510641, China b School of Materials Science and Engineering, PCFM Lab, Sun Yat-sen University, Guangzhou 510275, China c School of Pharmacy, Hainan Medical University, Haikou 571199, China Supporting Information Placeholder KEYWORDS: cobalt catalysis, coupling-cyclization, -diazoketones, Wolff rearrangement, quaternary 2-oxindoles. R N Ar
N
R N
O
O +
H R = alkyl and aryl
Ar
CO2Et Co(III) cat. -N2
Ar
NO Co
•
R N Ar O
O
-NO
CO2Et Ar up to 86% yield 30+ examples Combination of cobalt-catalyzed Csp2-H activation/Wolff rearrangement Rapid access system for all-carbon quaternary center synthesis N2
Ar EtO2C
ABSTRACT: An unusual cobalt(III)-catalyzed cross-coupling/cyclization of aryl C-H bonds of N-nitrosoanilines with -diazo-ketoesters has been achieved. This protocol features a unique combination of Csp 2-H activation/Wolff rearrangement process, allowing for the rapid assembly of quaternary 2-oxindoles. The empirical evidence and density functional theory (DFT) calculations reveal the trapping process of transient acceptor ketene intermediates by cobalt metallocycles.
Ketenes are extremely important transient synthons in organic chemistry.1 Over the past decades, transition metalcatalyzed cycloaddition and cross-coulping of ketenes with different reaction partners have been evidenced to enable assembly of complex carbonyl compounds, 2 in which most types of ketenes belong to donor ketenes such as -alkyl ketenes and -alkylaryl ketenes (generated in situ from acyl chlorides). 2j,2k In comparison, the chemical transformations involving acceptor ketenes such as -acyl ketenes have not been well established even under the photolysis and high-temperature conditions, possibly due to that acceptor ketenes are frequently unavailable,3 albeit various acceptor ketenes could provide a potential platform to construct structurally diverse carbonyl compounds. Therefore, developing new and efficient catalytic systems to trap transient acceptor ketenes under mild conditions is highly desirable. Direct carbenoid functionalization of inert C-H bonds belongs to one of the most challenging topics in organic synthesis.4 Recently, chelation-assisted cross-coupling of C-H bonds with diazo compounds has been extensively investigated for site-selectively installing a new C-C bond onto a coupling partner.5 Most particularly, cobalt-catalyzed C-H functionali-
zation has aroused great attention due to its low cost and environmental benignity.6,7 In this context, Glorius,8 Ackermann9 and Wang10 successively reported the Co(III)-catalyzed crosscoupling of aryl C-H bonds with diacceptor diazo compounds through carbene migratory insertion under chelation-assistance of pyridines, ketamines, amidines, and pyrazoles (Scheme 1a). However, transition metal-catalyzed Wolff rearrangement of diazo compounds still remains rather elusive under C-H activation system. Up to now, only noble metal salts could allow for the Wolff rearrangement of -diazoketones, resulting in the formation of donor ketenes (Scheme 1b),11 but earthabundant 1st-row transition metal-catalyzed Wolff rearrangement has not been reported yet. As the continuation of our interest in cobalt-catalyzed C-H functionalization,12 we herein explored a unprecedented cyclic coupling of Nnitrosoanilines13 (A) with diacceptor diazo compounds, in which cobalt complex-promoted Wolff rearrangement delivered acceptor -acyl ketenes. This protocol represents a unique platform to combine C-H activation/Wolff rearrangement for assembling quaternary 2-oxindoles14 (C) (Scheme 1c), which are the cornerstone of many natural products and medicinal molecules.15
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a) The General reaction pathway about Co(III)-catalyzed chelation-assisted C-H carbenoid insertion DG
DG Co(III)
Ar
O + Co(III) R1
Ar
H
DG
2
CO2R N2
Ar
O
Co
-N2
DG Co
Ar R1
R2O2C
10
Cp*Co(CO)I2
FeCl3
DCE
11d
11
Cp*Co(CO)I2
Cu(OAc)2
DCE
