3-Allyl-4-hydroxycoumarins and 4-allyl-3-hydroxycoumarins are obtained in 90%92% yields by the thermal [3,3] sigmatropic rearrangement of the corresponding ethers. 3-Allyl-4-hydroxy-6-methylpyrone is obtained from the direct alkylation of 4-hydroxy-6-methylpyrone with allyl halide. These substrates on treatment with SnCl4I2 at 25 °C give a mixture of both 5-exo- and 6-endo-cyclization products. However, regioselective formation of 5-exo products is observed when the reactions are conducted at lower temperatures (05 °C, kinetically controlled), while the reaction at a higher temperature (50 °C, thermodynamically controlled) affords regioselectively 6-endo cyclization products.Key words: stannic chloride, iodine, claisen rearrangement, 6-endocyclization, 5-exocyclization, kinetically controlled reaction, thermodynamically controlled reaction.
3-烯丙基-
4-羟基
香豆素和4-烯丙基-3-羟基
香豆素通过对应醚的热[3,3] sigmatropic重排反应以90%-92%的收率得到。3-烯丙基-
4-羟基-6-甲基
吡喃通过
4-羟基-6-甲基
吡喃与烯丙基卤化物的直接烷基化得到。这些底物在与SnCl4-I2在25°C处理时会产生一种既有5-内环反应产物又有6-外环反应产物的混合物。然而,当反应在较低温度(0-5°C,动力学控制)下进行时,观察到5-外环产物的选择性形成,而在较高温度(50°C,热力学控制)下进行的反应则选择性地生成6-内环产物。关键词:
氯化锡、
碘、克莱森重排反应、6-内环化、5-外环化、动力学控制反应、热力学控制反应。