Department of Chemistry , The University of Vermont , Burlington , Vermont 05405 , United States.
Department of Chemistry , Zhejiang University , Hangzhou 310027 , China.
J Am Chem Soc. 2019 Feb 27;141(8):3558-3565. doi: 10.1021/jacs.8b12420. Epub 2019 Feb 13.
Vinyl cations derived from diazo ketones participate in transition-metal-free C-H insertion reactions, but the corresponding amide and ester analog exhibit divergent reactivity profiles. Whereas cations formed from diazo ketones undergo a rearrangement and C-H insertion sequence, those from diazo amides do so less efficiently and tend to be competitively trapped before the insertion step occurs. Diazo esters undergo several rearrangement steps and fail to insert. DFT calculations reveal that this disparity stems from two factors: differing levels of electrostatic stabilization of the initially formed vinyl cation by the adjacent carbonyl oxygen and predistortion of the ketone and amide systems toward C-H insertion. The computational data is in strong agreement with experimental results, and this study explains how structural and electronic factors determine the outcome of reactions of diazo carbonyl-derived vinyl cations.
由重氮酮衍生的乙烯基阳离子参与无过渡金属的 C-H 插入反应，但相应的酰胺和酯类似物表现出不同的反应性。重氮酮形成的阳离子经历重排和 C-H 插入序列，而重氮酰胺形成的阳离子则效率较低，并且在插入步骤发生之前往往会被竞争性捕获。重氮酯经历几个重排步骤，无法插入。DFT 计算表明，这种差异源于两个因素：相邻羰基氧对最初形成的乙烯基阳离子的静电稳定程度不同，以及酮和酰胺系统向 C-H 插入的预变形。计算数据与实验结果非常吻合，该研究解释了结构和电子因素如何决定重氮羰基衍生的乙烯基阳离子反应的结果。
