烯丙位和高烯丙位酰胺基环烯烃环氧化的非对映选择性

五到七元环的烯丙位酰胺基环烯烃在有机溶剂中环氧化均得到很好的顺式立体选择性. 但对于高烯丙位酰胺基取代的环戊烯环氧化的非对映选择性则取决于具体的酰胺基: 4-乙酰胺基环戊烯得到与烯丙位系列类似的很好的顺式选择性, 但是4-苯甲酰胺基环戊烯环氧化的选择性变差. 对于高烯丙位环己烯系列, 4-乙酰胺基环己烯得到的是相应的顺式环氧化物, 而4-苯甲酰胺基环己烯环氧化除了得到顺式环氧产物以外, 还得到可能由反式环氧化物分子内环化生成的另一化合物: 外型-2-氧杂-3-苯基-4-氮杂双环[3.3.1]壬-3-烯-8-醇. 量子化学计算及其衍生物的环氧化结果支持这一结论. 该类高度顺式非对映选择性的酰胺基取代环烯烃的环氧化可用于具有特定立体结构的类似物的合成.

Diastereoselectivity in Epoxidation of Allylic and Homoallylic Amidocycloalkenes of Varied Size

Epoxidation of allylic amidocycloalkenes of five to seven membered rings consistently showed qualified syn-stereoselectivity. However, the cis-selectivity of homoallylic amido cyclopentene was related to the specific amido group. Epoxidation of 4-acetamidocyclopentene furnished good diastereoselectivity comparable to that of allylic ones. But 4-benzamidocyclopentene was epoxidized to obtain a relatively poor cis-selectivity. As to the homoallylic cyclohexene series, epoxidation of 4-acetamidocyclohexene afforded the corresponding cis-epoxide, whereas 4-benzamidocyclohexene gave, besides the cis-epoxide, an unex- pected product: exo-2-oxa-3-phenyl-4-azabicyclo[3.3.1]non-3-en-8-ol that might be formed from an in- tramolecular cyclization of the virtual trans-epoxide. The quantum calculations and the results of the epoxi- dation of the derivatives supported this mechanism. The highly cis-stereoselective epoxidation of the ami- docycloalkenes could be used to the synthesis of the stereodefined analogues.