3-hydroxyphenyl-substituted dihydrofurans fused with a cyclohexane 1a−c exclusively gave the corresponding syn/anti-stereoisomeric mixtures of dioxetanes 2a−c. The syn/anti-π-facial selectivity in the 1,2-cycloaddition of singlet oxygen (1O2) was found to be remarkably sensitive to the solvent as well as the reaction temperature. In fact, the solvent effect was so conspicuous that inversion of the syn/anti-π-facial selectivity
将3-羟基苯基取代的二氢
呋喃与
环己烷1a - c熔融进行单线加氧,仅得到相应的二氧杂
环丁烷2a - c的正/反立体异构混合物。发现在单线态氧(1 O 2)的1,2-环加成中的顺/反-π表面选择性对溶剂以及反应温度非常敏感。实际上,溶剂的作用是如此明显,以至于syn / anti的反转在不同的溶剂如
氯仿和
甲苯中观察到-π表面选择性。L
SER(线性溶剂能关系)分析表明,
路易斯酸度/碱度和HBD(氢键供体)/ HBA(氢键受体)能力以及溶剂的双极性/极化率在此变化中起重要作用在顺/反-π面部选择性。对单线态加氧的温度依赖性的研究表明,从1 O 2到1的顺式/反-π-面部选择性1,2-环加成反应是构象(熵)控制的过程。