Porras-Santos Luis F, Sandoval-Lira Jacinto, Hernández-Pérez Julio M, Quintero Leticia, López-Mendoza Pedro, Sartillo-Piscil Fernando
Centro de Investigación de la Facultad de Ciencias Químicas, Benemérita Universidad Autónoma de Puebla (BUAP), 14 Sur Esq. San Claudio, Col. San Manuel 72570, Puebla, Mexico.
Departamento de Ciencias Básicas, TecNM campus Instituto Tecnológico Superior de San Martín Texmelucan, Camino a la Barranca de Pesos, San Martín Texmelucan 74120, Puebla, Mexico.
J Org Chem. 2024 Aug 16;89(16):11281-11292. doi: 10.1021/acs.joc.4c00978. Epub 2024 Aug 5.
The TEMPO oxoammonium cation has been proven to be both an efficient oxidizing reagent and an electrophilic substrate frequently found in organic reactions. Here, we report that this versatile chemical reagent can also be used as an efficient promoter for C- and N-glycosylation reactions through a Ferrier rearrangement with moderate to high yields. This unprecedented reactivity is explained in terms of a Lewis acid activation of glycal by TEMPO forming a type of glycal-TEMPO mesomeric structure, which occurs through an extended vinylogous hyperconjugation toward the π* orbital [LP → π*, π* → σ*, and LP → π*]. This enables the formation of the respective Ferrier glycosyl cation, which is trapped by various nucleophiles. The extended hyperconjugation (or double hyperconjugation) toward the π* orbital, which confers the Lewis acid character of the TEMPO cation, was supported by natural bond orbital analysis at the M06-2X/6-311+G** level of theory.
TEMPO氧鎓阳离子已被证明既是一种有效的氧化试剂，又是有机反应中常见的亲电底物。在此，我们报道这种多功能化学试剂还可通过费里尔重排用作C-和N-糖基化反应的有效促进剂，产率适中至较高。这种前所未有的反应活性可通过TEMPO对烯丙基醇的路易斯酸活化来解释，形成一种烯丙基醇-TEMPO共振结构，这是通过向π轨道的扩展乙烯型超共轭[孤对电子→π，π*→σ*，以及孤对电子→π*]发生的。这使得能够形成相应的费里尔糖基阳离子，该阳离子被各种亲核试剂捕获。在M06-2X/6-311+G*理论水平下的自然键轨道分析支持了向π轨道的扩展超共轭（或双超共轭），这赋予了TEMPO阳离子路易斯酸性质。
