conformation to one which is characterized by a diastereo-zeroplane consisting of the s-trans vinyl group, the stereogenic center and the methyl group (Fig. 3). A stereochemical model of the transition state for [2+2]cycloaddition of chlorosulfonyl isocyanate and vinyl ethers is proposed, based on the lowest energy conformation derived from NOE coefficients, which agrees well with the experimental facts and provides
将
乙烯基取代的
异丙基醚测得的稳态NOE系数与由分子力学程序生成的构象进行比较,可以表征最有利的基态构象。具有高置信度,可以将最低的能量构象分配给一个特征,该构象的特征是由反式
乙烯基,立体异构中心和
甲基组成的非对映零平面(图3)。基于NOE系数的最低能量构象,提出了
氯磺酰基
异氰酸酯和
乙烯基醚的[2 + 2]环加成过渡态的立体
化学模型,该模型与实验事实吻合得很好,并提供了合理的解释方向。不对称感应。