Ali Shaikh A, Iman Muhammad Z N, Wazeer Mohamed I M, Fettouhi Mohammed B
Chemistry Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia.
Spectrochim Acta A Mol Biomol Spectrosc. 2008 Aug;70(3):482-90. doi: 10.1016/j.saa.2007.07.032. Epub 2007 Jul 31.
A series of (betaR,5R)- and (betaR,5S)-2,5-disubstituted isoxazolidines: 5-(substituent)-beta-phenyl-2-isoxazolidineethanols, have been prepared by asymmetric nitrone cycloaddition reactions and their NMR spectra recorded over a wide range of temperatures. The spectra at low temperatures indicate the presence of the (betaR,5S) diasteromer almost exclusively as a single invertomer having trans disposition of the substituents at N(2) and C(5), while the (betaR,5R) diasteromer remained as a mixture of two interconverting invertomers in deuterated chloroform. The effect of H-bonding - intramolecular in CDCl(3) and intermolecular in CD(3)OD - on the population ratio of the invertomers and nitrogen inversion process has been investigated. The nitrogen inversion barriers are determined using complete line-shape analysis, and their dependence on solvent is discussed. Due to steric factor the trans-invertomers are found to be more stable than their cis counterparts.
通过不对称硝酮环加成反应制备了一系列（βR，5R）-和（βR，5S）-2,5-二取代异恶唑烷：5-（取代基）-β-苯基-2-异恶唑烷乙醇，并在很宽的温度范围内记录了它们的核磁共振谱。低温下的谱图表明，（βR，5S）非对映异构体几乎完全以单一的反转异构体形式存在，其N(2)和C(5)上的取代基呈反式排列，而（βR，5R）非对映异构体在氘代氯仿中则以两种相互转化的反转异构体混合物形式存在。研究了氢键（在CDCl₃中为分子内氢键，在CD₃OD中为分子间氢键）对反转异构体的种群比例和氮反转过程的影响。使用完整的线形分析确定了氮反转势垒，并讨论了它们对溶剂的依赖性。由于空间因素，发现反式反转异构体比其顺式对应物更稳定。
