Issue 59, 2016, Issue in Progress

Theoretical investigations toward the [3 + 2]-dipolar cycloadditions of nitrones with vinyldiazoacetates catalyzed by Rh2(R-TPCP)4: mechanism and enantioselectivity

Abstract

The mechanism of Rh2(R-TPCP)4-catalyzed [3 + 2]-dipolar cycloadditions between vinyldiazoacetate and nitrone to form 2,5-dihydroisoxazole has been studied by ONIOM methodology calculations including density functional theory and semi-empirical PM6 theory. This mechanism begins with carbenoid formation catalyzed by a rhodium catalyst, followed by vinylogous addition/cyclization of an iminium to construct a five-membered ring isoxazolidines, and followed by the functionalization processes of 1,3-hydride abstraction/proton transfer to generate 2,5-dihydroisoxazoles. The calculated results indicate a distinct stepwise fashion of this [3 + 2]-cycloaddition because of the extremely transient intermediate that emerged in the vinylogous reaction, and the cyclization of iminium addition is deemed to be the enantio-controlling step. According to analysis of thermodynamic information, the process of protonation has the highest energy barrier in this catalytic cycle and is determined as the rate-controlling step. A higher enantioselective formation of (R)-2,5-dihydroisoxazole derived from the reaction between aryl nitrone and s-trans vinylcarbenoid is evaluated. What's more, we kinetically analyze the enantioselectivity of this complete catalytic cycle by the AUTOF program and provide the reactivity trends with an activation strain model.

Graphical abstract: Theoretical investigations toward the [3 + 2]-dipolar cycloadditions of nitrones with vinyldiazoacetates catalyzed by Rh2(R-TPCP)4: mechanism and enantioselectivity

Supplementary files

Article information

Article type
Paper
Submitted
26 Mar 2016
Accepted
18 May 2016
First published
19 May 2016

RSC Adv., 2016,6, 53839-53851

Theoretical investigations toward the [3 + 2]-dipolar cycloadditions of nitrones with vinyldiazoacetates catalyzed by Rh2(R-TPCP)4: mechanism and enantioselectivity

L. Ma, W. Wang and G. Wang, RSC Adv., 2016, 6, 53839 DOI: 10.1039/C6RA07873G

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