substitution on the diene. Cyclic dienes react with the oxyallyl cation by forming only one carbon-carbon bond, but the site of bond formation can be affected by steric hindrance. Electron-rich alkenes intercept the allyl cation by forming one carbon-carbon bond, or two carbon-carbon bonds through [3 + 2] cyclization. In some instances, further treatment of the initial products with BF(3) x Et(2)O leads
用 BF(3) x Et(2)O 处理
丙二烯基
乙烯基酮会通过 Nazarov 反应生成环状氧烯丙基阳离子,当该反应在无环二烯存在下进行时,[4 + 3] 和 [3] + 2] 产品以高区域和立体选择性有效获得。[4 + 3] 与 [3 + 2] 产物的比例取决于二烯上的取代。环状二烯通过仅形成一个碳-碳键与氧烯丙基阳离子反应,但键形成的位置会受到空间位阻的影响。富电子烯烃通过[3+2]环化形成一个碳-碳键或两个碳-碳键来拦截烯丙基阳离子。在某些情况下,用 BF(3) x Et(2)O 进一步处理初始产品会导致平衡产品的产量良好。