Starting with 2-methyl-5:7-dihydroxychromone, an allyl group is introduced into the 6-position by Claisen migration of a 5-allyl ether. The initial protection of the 7-hydroxyl is best effected by tosylation. If the tosyl group is removed before Claisen migration and the C-allyl compound subjected to ozonolysis and ring closure, norvisnagin is obtained in a poor yield and can be methylated to visnagin
从2-甲基-5:7-二羟基
色酮开始,通过5-
烯丙基醚的克莱森迁移将烯丙基引入6-位。
甲苯磺酰化对7-羟基的初始保护效果最好。如果在克莱森(Claisen)迁移之前去除了
甲苯磺酰基,并且对C-烯丙基化合物进行了
臭氧分解和闭环反应,则制得的去甲炔那诺的收率很低,可以被甲基化为visnagin。在另一种方法中,
甲苯磺酰基在
臭氧分解之前被除去。为此目的,先前5-位甲基化是有利的。该途径可直接以良好的产量提供维珍素。