Studies on the benzoxazine series. Part 3—Preparation and13C NMR structural Study of γ Effects of SomeN-substituted 3,4-dihydro-2H-1,3-benzoxazines
作者:Kari Neuvonen、Kalevi Pihlaja
DOI:10.1002/mrc.1260280309
日期:1990.3
Seventeen N-substituted 3,4-dihydro-2H-1,3-benzoxazines [N-substituent = Et, Pri, But, CH2C6H5 or CH(CH3)C6H5] were prepared and their structures studied in the light of 13C chemical shifts. The γ effects caused by C(α)-methyl or C(α)-phenyl substitution at the heterocyclic ring carbons were found to be valuable structural parameters. By using N-tert-butyl derivatives as models, and by dividing γtot effects into their components, the rotamer populations due to the rotation around the NC(α) bond could be evaluated. The method also allows the configurational assignment of diastereomeric N-α-methylbenzyl derivatives. The effect of the half-chair structure on the 13C NMR parameters is discussed.
研究人员制备了 17 种 N 取代的 3,4-二氢-2H-1,3-苯并噁嗪[N 取代基 = Et、Pri、But、CH2C6H5 或 CH(CH3)C6H5],并根据 13C 化学位移研究了它们的结构。研究发现,杂环碳原子上的 C(α)-甲基或 C(α)-苯基取代引起的 γ 效应是有价值的结构参数。通过使用 N-叔丁基衍生物作为模型,并将γtot 效应分成不同的部分,可以评估围绕 NC(α)键旋转所产生的旋转体群。该方法还可以对非对映的 N-α-甲基苄基衍生物进行构型分配。该方法还讨论了半椅结构对 13C NMR 参数的影响。