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Mechanism and Selectivity Investigation on Dirhodium-Catalyzed C–H Functionalization of N-Arylpiperidines: A Computational Study
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DOI:10.1039/D6NJ01693F.png)
Abstract
En 中文
Rhodium catalysts exhibit high yields and excellent regio-; stereo- and enantioselectivity in C-H functionalization; providing a streamlined route to the synthesis of drug target. In this study; density functional theory (DFT) calculations were performed to illustrate the reaction mechanism; regio- and stereoselectivity of dirhodium-catalyzed piperidine transformations. The computational results indicate that the reaction proceeds through three steps: (i) coordination of the dirhodium catalyst with the diazo compound to form a rhodium carbene intermediate; (ii) C-H bond activation of piperidine by this carbene; and (iii) C-C coupling to yield the C-H functionalized product. In the overall catalytic cycle; the formation of the rhodium carbene intermediate is the rate-determining step. The model catalyst Rh₂(OAc)₄ adequately describes the catalytic mechanism and regioselectivity of asymmetric C-H functionalization but fails to account for enantioselectivity; which could only be explained by real chiral large ligands. Charge analysis on piperidines confirms that electronic effects of substituent regulate the regioselectivity and yield. The enantioselectivity of the reaction is controlled not only by the weak interactions between the rhodium carbene and piperidine; but also by the deformation energy of the transition-state.
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