描述了由水杨醛和α-烯丙基化的醇产生的邻醌甲基的分子内[4 + 2]环加成反应。在催化量的苯磺酸(BSA)的存在下,反应在EtOH中顺利进行,通过三键形成工艺以中等至极好的收率和高的非对映选择性提供了呋喃[3,2- c ]苯并吡喃。该反应提供了一个简单而直接的方案,可以有效地构建呋喃[3,2- c ]苯并吡喃骨架。提出了一种可能的机制,包括半缩醛形成/杂-Diels-Alder反应,以使观察到的结果合理化。
General and Highly α-Regioselective Zinc-Mediated Prenylation of Aldehydes and Ketones
摘要:
A simple, efficient, and general alpha-prenylation approach for the synthesis of a variety of alpha-prenylated alcohols has been successfully developed. A wide range of alpha-prenylated alcohol derivatives could be obtained in good yields by highly alpha-regioselective zinc-mediated prenylation of various aldehydes and ketones with prenyl bromide at 120 degrees C in HMPA. By simply altering the reaciton solvent and temperature, the method allows the achievement of a highly notable opposite regiocontrol, providing the expected regiochemical product. The method provides a convenient route for the direct alpha-prenylation of carbonyl compounds in a highly alpha-regioselective manner using a cheap and convenient mediator. Two possible pathways are proposed to account for the formation of these synthetically difficult-to-obtain molecules.