total synthesis of the natural stilbene (+)-schweinfurthin G (8) has been accomplished through a sequence based on an efficient cationic cascade cyclization. This cascade process is initiated by Lewis acid promoted ring opening of an epoxide and terminated through a novel reaction with a phenolic oxygen "protected" as its MOM ether. Several Lewis acids have been examined for their ability to induce
天然
二苯乙烯 (+)-schweinfurthin G (8) 的全合成已通过基于有效阳离子级联环化的序列完成。该级联过程由
路易斯酸促进
环氧化物的开环引发,并通过与作为其 MOM 醚“保护”的
酚氧发生新反应而终止。已经检查了几种
路易斯酸诱导这种新反应的能力,发现
BF3 x Et2O 是最有效的。在这些条件下唯一的主要副产物是预期的仲醇被发现为其 MOM 醚衍
生物(例如,30)。虽然这种副产物可以通过
水解转化为原始的目标化合物,它还可以用作受保护的醇,以允许在不使仲醇脱
水的情况下制备苄基
膦酸酯 (43)。所得的
膦酸酯用于与代表目标化合物右半部分的醛的 Horner-Wadsworth-EmMOns 缩合反应,这是对先前基于右半
膦酸酯和左半醛缩合的研究的补充。