TY - JOUR
T1 - Chemoselective Catalytic Dehydrogenative Cross-Coupling of 2-Acylimidazoles
T2 - Mechanistic Investigations and Synthetic Scope
AU - Tanaka, Tsukushi
AU - Hashiguchi, Kayoko
AU - Tanaka, Takafumi
AU - Yazaki, Ryo
AU - Ohshima, Takashi
N1 - Funding Information:
This work was financially supported by JSPS KAKENHI Grant Number JP15H05846 in Middle Molecular Strategy, JP16H01032 in Precisely Designed Catalysts with Customized Scaffolding, Grant-in-Aid for Scientific Research (C) (#16K08166), and Platform Project for Supporting Drug Discovery and Life Science Research (Basis for Supporting Innovative Drug Discovery and Life Science Research (BINDS)) from AMED under Grant Number JP17am0101091. R.Y. thanks the Sumitomo Foundation for financial support.
Publisher Copyright:
© 2018 American Chemical Society.
PY - 2018/9/7
Y1 - 2018/9/7
N2 - Chemoselective iron-catalyzed dehydrogenative cross-coupling using 2-acylimidazoles is described. The addition of a phosphine oxide ligand substantially facilitated the generation of tert-butoxy radicals from di-tert-butyl peroxide, allowing for efficient benzylic C-H bond cleavage under mild conditions. Extensive mechanistic studies revealed that the enolization of 2-acylimidazole proceeded through dual iron catalyst activation, followed by subsequent chemoselective cross-coupling with a benzyl radical over an undesired benzyl radical-derived homocoupling dimer that inevitably formed in earlier reported conditions. A variety of alkylarenes, aliphatic alkane, and functionalized 2-acylimidazoles were applicable, demonstrating the synthetic utility of the present catalysis. Contiguous all-carbon quaternary carbons were constructed through dehydrogenative cross-coupling. The catalytic chemoselective activation of 2-acylimidazole over bidentate coordinative and much more acidic malonate diester was particular noteworthy. Catalytic oxidative cross-enolate coupling of two distinct carboxylic acid equivalents was also achieved using acetonitrile as a coupling partner.
AB - Chemoselective iron-catalyzed dehydrogenative cross-coupling using 2-acylimidazoles is described. The addition of a phosphine oxide ligand substantially facilitated the generation of tert-butoxy radicals from di-tert-butyl peroxide, allowing for efficient benzylic C-H bond cleavage under mild conditions. Extensive mechanistic studies revealed that the enolization of 2-acylimidazole proceeded through dual iron catalyst activation, followed by subsequent chemoselective cross-coupling with a benzyl radical over an undesired benzyl radical-derived homocoupling dimer that inevitably formed in earlier reported conditions. A variety of alkylarenes, aliphatic alkane, and functionalized 2-acylimidazoles were applicable, demonstrating the synthetic utility of the present catalysis. Contiguous all-carbon quaternary carbons were constructed through dehydrogenative cross-coupling. The catalytic chemoselective activation of 2-acylimidazole over bidentate coordinative and much more acidic malonate diester was particular noteworthy. Catalytic oxidative cross-enolate coupling of two distinct carboxylic acid equivalents was also achieved using acetonitrile as a coupling partner.
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U2 - 10.1021/acscatal.8b02361
DO - 10.1021/acscatal.8b02361
M3 - Article
AN - SCOPUS:85051194739
VL - 8
SP - 8430
EP - 8440
JO - ACS Catalysis
JF - ACS Catalysis
SN - 2155-5435
IS - 9
ER -