He Y, Xu DH, Zhang YJ, Zhang C, Guo JM, Li L, Liang XQ. Microscopic mechanism of light-induced tetrazole-quinone 1,3-dipolar cycloaddition: a MS-CASPT2 theoretical investigation.
RSC Adv 2021;
11:32792-32798. [PMID:
35493565 PMCID:
PMC9042216 DOI:
10.1039/d1ra04636e]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Accepted: 08/18/2021] [Indexed: 11/21/2022] Open
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.
The microscopic mechanisms of light-induced tetrazole-quinone 1,3-dipolar cycloaddition are elucidated using high level MS-CASPT2 calculations.![]()
Collapse