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A DFT Study on the Binuclear Copper(I)-Catalyzed Synthesis Mechanism of 1,2,3-Triazolo[1,5-c]Pyrimidine via Interrupted Click and Ketenimine Rearrangement
Authors:Zhaoman Zhou  Qianqian Yue  Prof?Dr Yanying Zhao
Institution:1. Department of Chemistry, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou, 310018 China

Office of Academic Research, Guangxi Modern Polytechnic College, Hechi, 547000 China;2. Department of Chemistry, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou, 310018 China

Abstract:In this paper, the mechanism of the full catalytic cycle for binuclear Cu(I)-catalyzed sulfonyl azide-alkyne cycloaddition reaction for the synthesis of triazolopyrimidines was rationalized by density functional theoretical (DFT) calculations. The computed reaction route consists of: (a) formation of dicopper intermediates, including C?H activation of terminal alkyne, 3+2 ring cycloaddition and ring-reducing reaction and transmetalation, (b) interrupted CuAAC reaction, including di-copper catalyzed ring-opening of 2H-azirines and C?C bond formation to generate the copper-triazoles and -ketenimines, (c) two-step C?N cross-coupling and following (d) multi-step hydrogen transfer by the hydrogen bonding chain of water to promote the C?N formation and another C?N cleavage through the removal of p-tolyl sulfonamides. Our DFT results indicate that the multi-step hydrogen transfer process is the rate-determining step along the potential energy surface profile. The explicit water model was used for systematic determination of barrier for C?C cross-coupling, C?N bond formation and cleavage, and p-tolylsulfonamide removal. A critical insight in the interrupted CuAAC reaction was proposed. Further prediction interprets H2O hydrogen bond chain plays an important role in C?N bond formation and cleavage, and the removal of p-tolylsulfonamide. This may have fundamental guidance on the design of 1, 5-herterocyclic functionalized triazolopyrimidines via interrupted CuAAC rearrangement reaction, as well as hydrogen bond chain of water.
Keywords:crossing-coupling  C?N formation and cleavage  hydrogen transfer  ketenimine rearrangement  triazolopyrimidines
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