Theoretical investigations toward the [3 + 2]-dipolar cycloadditions of nitrones with vinyldiazoacetates catalyzed by Rh2(R-TPCP)4: mechanism and enantioselectivity. Issue 59 (3rd June 2016)

• Record Type: Journal Article
• Authors: Ma, Ling-Ling; Wang, Wan; Wang, Gui-Chang
• Is Part Of: RSC advances. Volume 6:Issue 59(2016)
• Page Start: 53839
• Page End: 53851
• Publication Date: 2016-06-03
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/c6ra07873g
• Languages: English
• ISSNs: 2046-2069

Abstract

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 PM6 theory. 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.