Herrera R, Nagarajan A, Morales M A, Méndez F, Jiménez-Vázquez H A, Zepeda L G, Tamariz J
Departamento de Química Orgánica, Escuela Nacional de Ciencias Biológicas, IPN, Prol. Carpio y Plan de Ayala, 11340 México.
J Org Chem. 2001 Feb 23;66(4):1252-63. doi: 10.1021/jo001393n.
Captodative olefins 1-acetylvinyl carboxylates proved to be highly regioselective dipolarophiles in 1,3-dipolar cycloadditon to propionitrile oxide, arylphenylnitrile imines, diazoalkanes, and nitrones to yield the corresponding 5-substituted heterocycles. The addition of the latter was also stereoselective, being slightly susceptible to steric demand of the carboxylate substituent in the olefin. All atempts to cleave the isoxazolidine N-O bond under reductive conditions failed, providing diverse products with side-group reduction. FMO theory was unsuccessful to explain the regioselectivity observed with nitrones, since the opposite orientation was predicted. The recently formulated DFT/HSAB theoretical model was able to rationalize this regioselectivity, identifying the nucleophilic and electrophilic atoms involved in the process via calculation of interaction energies, suggesting the specific direction of the electronic process at each of the reaction sites.
捕获型烯烃1-乙酰基乙烯基羧酸盐被证明是1,3-偶极环加成反应中高度区域选择性的亲偶极体，可与丙腈氧化物、芳基苯基腈亚胺、重氮烷和硝酮反应生成相应的5-取代杂环。与后者的加成反应也是立体选择性的，对烯烃中羧酸盐取代基的空间需求略有敏感。在还原条件下所有裂解异噁唑烷N-O键的尝试均失败，得到了带有侧基还原的多种产物。前线分子轨道理论无法解释观察到的与硝酮的区域选择性，因为预测的是相反的取向。最近提出的密度泛函理论/软硬酸碱理论模型能够解释这种区域选择性，通过计算相互作用能确定参与该过程的亲核和亲电原子，表明每个反应位点电子过程的特定方向。
