Wang Xiaochen group, Nankai University: Boron catalyzed negative hydrogen transfer induced cyclization

The functionalization of hydrocarbon bonds has been a hot topic in Chemistry for many years because of its rapid and convenient construction of carbon carbon bonds and carbon heterobonds Among them, the functionalization of a-position hydrocarbon bond of nitrogen atom mainly includes: (1) reaction with alkyllithium reagent to generate lithium compound and then react with electrophilic reagent; (2) oxidation to generate imine positive ion and then react with nucleophilic reagent; (3) transition metal catalyzed activation of hydrocarbon bond; (4) insertion reaction of metal carbene However, these methods usually require the use of equivalent organometallic reagents or oxidants, or the use of transition metal catalysts In addition, the intramolecular cyclization induced by negative hydrogen transfer can generate various heterocyclic compounds through the cyclization induced by 1,5-hydrogen transfer at the α position This kind of reaction requires that the substrate contains negative hydrogen acceptors (such as carbonyl, imine, electron deficient olefin, etc.), and in order to improve the reaction activity, Lewis acid or protonic acid is usually added to coordinate with the negative hydrogen acceptor to enhance the electrophilicity of the acceptor In general, the substrate without negative hydrogen receptor can not react Recently, Wang Xiaochen, State Key Laboratory of elemental organic chemistry, Nankai University, used B (C6F5) 3 as transient negative hydrogen acceptor to realize the intramolecular cyclization of N, N-dialkyl aromatic amines substituted by o-alkenes It should be noted that this kind of substrate does not contain negative hydrogen acceptor and can not react without boron catalyst The mechanism study shows that B (C6F5) 3 first grabs the negative hydrogen ion at the nitrogen a position to generate imine positive ion and boron hydrogen negative ion, then olefin attacks imine positive ion to generate cyclization reaction and carbonium intermediate, and finally negative hydrogen and carbonium ion generate addition reaction The reaction substrate has a wide range and good functional group compatibility It can be used to prepare some nitrogen heterocyclic compounds which are difficult to be synthesized by other methods This achievement was recently published in ACS Catalysis (DOI: 10.1021 / acscalal 8b04485) Third year master students Tian Junjie and Zeng Ningning are co authors of the paper The research was supported by the Central Organization Department's thousand talents program, the Foundation Committee, Tianjin Science and Technology Commission, the Ministry of education and Nankai University.