Chinese Journal of Organic Chemistry >
A Density Functional Theory Study of the Mechanism of Cu(II)-Catalyzed Synthesis of Pyrido[1,2-a]benzimidazoles
Received date: 2015-02-06
Revised date: 2015-03-14
Online published: 2015-04-10
Supported by
Project supported by the National Natural Science Foundation of China (No. 21103072) and the Fundamental Research Funds for the Central Universities (No. 21615405).
The reaction mechanism of Cu(II)-catalyzed synthesis of pyrido[1,2-a]benzimidazoles was theoretically investigated with the aid of density functional theory calculations (DFT) at the B3LYP level. Five possible mechanisms for the synthesis were proposed: (1) C—H-bond-breaking step preceding deprotonation of imino group, and finally C—N bond formation (Pathway a), (2) deprotonation of imino group preceding C—H-bond-breaking step, and finally C—N bond formation (Pathway b), (3) C—H-bond-breaking as the first step, then C—N bond formation preceding deprotonation of imino group (Pathway c), (4) the anti-imino-cupration mechanism (Pathway d), (5) the Friedel-Crafts alkylation mechanism (Pathway e). The calculation results indicate that the most favorable pathway involves C—H bond breaking by concerted metalation/deprotonation (CMD), followed by N—H deprotonation along the triplet state and C—N bond formation (Pathway a). A clear understanding of the reaction mechanism of pyrido[1,2-a]benzimidazoles formation should lead to more efficient synthetic strategies.
Du Lijuan , Wu Caihong , Gu Honghong , Li Juan . A Density Functional Theory Study of the Mechanism of Cu(II)-Catalyzed Synthesis of Pyrido[1,2-a]benzimidazoles[J]. Chinese Journal of Organic Chemistry, 2015 , 35(8) : 1726 -1732 . DOI: 10.6023/cjoc201501034
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