期刊
ORGANIC & BIOMOLECULAR CHEMISTRY
卷 14, 期 46, 页码 10875-10885出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c6ob01901c
关键词
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资金
- National Natural Science Foundation of China [21402158]
- Education Department of Sichuan Province [14ZB0131]
- Xihua University [Z1313319]
- Open Research Subject of Key Laboratory (Research center for advanced computation) of Xihua University [szjj2015-051]
The carboxylative cyclization of a propargyl alcohol with CO2 mediated by a N-heterocyclic olefin (NHO) or N-heterocyclic carbene (NHC) has been comparatively studied using density functional theory (DFT) calculations. The calculations show that the advantageous catalytic performance of the NHO in the title reaction can be attributed to two aspects: (i) the active site of the NHO extends outside the imidazolium ring, which enhances the reactivity and stability of the [NHOH](+)[carbonate](-) ionic pair intermediate. Thus, the turnover frequency (TOF)-determining intramolecular cyclization step is kinetically more favorable in the NHO system. (ii) As the basicity of the NHO is weaker than the NHC, deprotonation of the propargyl alcohol by the NHO is relatively more difficult. Consequently, the side reaction of ring-opening transesterification of the alpha-alkylidene cyclic carbonate with the nucleophilic [NHOH](+)[alkoxide](-) ionic pair intermediate can be inhibited using the NHO system. The present mechanistic study provides a basis for further application of these promising organocatalysts in more organic transformations.
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