摘要/Abstract

通过密度泛函理论（DFT）方法分别研究了银和钪催化重氮化合物与1，3-二羰基化合物C—C键和C—H键插入的反应机理以及反应具有化学选择性的原因.计算研究表明，重氮化合物首先与Ag和Sc反应形成相应的银卡宾和钪卡宾.配位数低的银卡宾与1，3-二羰基化合物经过亲电加成、分子内环化、选择性开环和烯醇异构等过程，选择性地发生C—C键插入反应，生成α-位含全碳季碳中心的1，4-二羰基化合物.配位数高的钪卡宾与1，3-二羰基化合物经过亲电加成和质子化过程，选择性地发生C—H键插入反应，生成α-位含叔碳中心的1，3-二羰基化合物.理论计算表明，关键过渡态的环张力以及银和钪金属中心配位数的差异共同影响了该反应的化学选择性.该结果为发展过渡金属催化的卡宾转移反应提供了新思路.
关键词: 密度泛函理论, 银卡宾, 钪卡宾, 化学选择性
Density functional theory (DFT) calculations were carried out to investigate the mechanism and chemoselectivity of silver-or scandium-catalyzed insertion of diazo compounds into C-C or C-H bonds of 1,3-dicarbonyl compounds. The results show that silver and scandium carbenes are readily generated by metal-induced extrusion of nitrogen from diazo compounds. When low-coordinated silver(I) is used as the catalyst, carbene insertion into the C-C bond of 1,3-dicarbonyls leads to 1,4-dicarbonyl product containing an all-carbon α-quaternary center, through a cascade sequence of electrophilic addition, intramolecular cyclization, selective ring-opening and enol isomerization. When highly coordinated scandium(III) is used, carbene insertion into C-H bond of 1,3-dicarbonyls leads to 1,3-dicarbonyl product containing α-tertiary center, through a cascade sequence of electrophilic addition and protonation. Computational studies show that the chemoselectivity results from the cooperative effect of ring tension and the difference in coordination number of metal centers, which provides useful insight into the development of transition metal-catalyzed carbene transfer reactions.
Key words: density functional theory, silver carbenoid, scandium carbenoid, chemoselectivity


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