Issue 52, 2021

Microscopic mechanism of light-induced tetrazole-quinone 1,3-dipolar cycloaddition: a MS-CASPT2 theoretical investigation

Abstract

Recently, experimentalists have developed a green and efficient method to synthesize pyrazole-fused quinones through light-induced tetrazole-quinone 1,3-dipole cycloadditions. However, the underlying microscopic mechanisms remain to be clarified. In this work, we have employed several electronic structure calculation methods (MS-CASPT2, CASSCF, DFT) to systematically explore the microscopic mechanism of related light-induced reactions and deactivation pathways. Upon excitation with ultraviolet light, one of the original reactants 2-(4-fluorophenyl)-5-phenyl-2H-tetrazole (FPT) reaches its S1 excited state. After that, due to the ultrahigh energy and the small energy barrier, the FPT molecule breaks the N2–N3 and N4–C5 bonds sequentially, removing the nitrogen atom finally in the S1 state. Combined with the cleavage of the second N4–C5 bond, the system reaches its conical intersection region and deactivates ultrafast to the ground state, generating the active intermediate ((4-fluorophenyl)diazen-1-ium-1-ylidene) (phenyl)methanide (FPNI). Subsequently, the active intermediate FPIN can react with naphthoquinone in the ground state by overcoming an energy barrier of about 5.7 kcal mol−1, after which the 1-(4-fluorophenyl)-3-phenyl-1H-benzo[f]indazole-4,9(3aH, 9aH)-dione (FP2HQ) is formed. The FP2HQ can be oxidized to obtain the 1-(4-fluorophenyl)-3-phenyl-1H-benzo[f]indazole-4,9-dione (PFQ). Due to the high energy and small barrier, the entire reaction process can easily take place, which ultimately leads to the efficient reaction. Our present work not only explains the experimental mechanism in detail but can also be helpful for the future design of related photoinduced reactions with the aid of theoretical calculations.

Graphical abstract: Microscopic mechanism of light-induced tetrazole-quinone 1,3-dipolar cycloaddition: a MS-CASPT2 theoretical investigation

Supplementary files

Article information

Article type
Paper
Submitted
15 Jun 2021
Accepted
18 Aug 2021
First published
05 Oct 2021
This article is Open Access
Creative Commons BY-NC license

RSC Adv., 2021,11, 32792-32798

Microscopic mechanism of light-induced tetrazole-quinone 1,3-dipolar cycloaddition: a MS-CASPT2 theoretical investigation

Y. He, D. Xu, Y. Zhang, C. Zhang, J. Guo, L. Li and X. Liang, RSC Adv., 2021, 11, 32792 DOI: 10.1039/D1RA04636E

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