Racemic 2-isopropyl-2-methylhex-5-enal has been synthesised in order to probe ene cyclisations leading to menthol analogues. The objective was first to discover catalytic conditions for preferential cyclisation to the menthol rather than the neomenthol series and then to develop (dynamic) kinetic resolution procedures which afforded a single enantiomer of product. It was found that catalytic quantities of both Me2AlCl and a bulky methylaluminium bis(phenoxide) reagent gave products attributed to a Meerwein-Pondorff-Verley reaction. In this the aldehyde is reduced to a primary alcohol and the ene product oxidised to the corresponding α,β-unsaturated ketone. By contrast, a related bulky chloroaluminium reagent catalysed the ene cyclisation cleanly, but preferentially to the undesired neomenthyl stereoisomer.
为了探索导致薄荷醇类似物的烯丙基化反应,合成了外消旋2-异丙基-2-甲基己-5-烯醛。首要目标是发现有利于烯丙基化生成薄荷醇而非新薄荷醇系列的催化条件,然后开发(动态)动力学分辨程序,以获得产品的单对映体。发现催化量的Me2AlCl和体积庞大的甲基铝双(酚氧基)试剂可产生与Meerwein-Pondorff-Verley反应相关的产物。在此反应中,醛被还原为初级醇,烯基产物被氧化为相应的α,β-不饱和酮。相比之下,相关的体积庞大氯化铝试剂催化的烯丙基化反应干净地进行,但更倾向于不受欢迎的新薄荷醇立体异构体。