Premium
Reagent addition sequence and equivalent in N‐heterocyclic carbene‐catalyzed nonpolar inversion enable conversion from aldimine to benzoxazole
Author(s) -
Li Xiaoyan,
Liu Jiabin,
Zhang QiaoChu,
Zhang Wenjing,
Lan Yu
Publication year - 2020
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.26249
Subject(s) - umpolung , chemistry , exothermic reaction , reagent , catalysis , benzoxazole , carbene , reaction mechanism , photochemistry , combinatorial chemistry , computational chemistry , organic chemistry , nucleophile
The umpolung reaction catalyzed by N‐heterocyclic carbenes (NHCs) has been widely studied and well recognized, but their role in the nonpolar inversion reaction under oxidative condition has been rarely reported. In this paper, the mechanism of the oxidative nonpolar inversion reaction catalyzed by NHCs to produce benzoxazole is investigated in detail. The reaction occurs through five processes. For oxidation in the second process, two successive tautomerizations followed by oxidation are energetically more favorable than the other two pathways. The rate‐determining step is the oxidation by 3,3′‐5,5′‐tetra‐ tert ‐butyl‐4,4′‐diphenoquinone. Mechanism calculations of the uncatalyzed reaction reveal that the very highly exothermic nature of the initial step is the main reason for the extremely high energy barrier in the following step. With the participation of NHC, this unfavorable transformation can be deftly prevented according to the specific sequence and equivalent of reagent addition, enabling the reaction to occur under mild conditions.