Protective group-free syntheses of four racemic pheromones with a 6,8-dioxabicyclo[3.2.1]octane ring were achieved in five or six steps from commercially available (±)-3-butyn-2-ol (6) and 2-alkenyl halides or 2-alken-1-ol by employing Lewis acid-catalyzed acetalization of δ, ε-epoxy ketones as the key reaction. (±)-Frontalin (1) was prepared in a 25% overall yield in five steps from methallyl chloride (5a), (±)-endo-brevicomin (2) was prepared in a 23% overall yield in five steps from (E)-2-pentenyl bromide (5b), and (±)-exo-brevicomin (3) and (±)-3,4-dehydro-exo-brevicomin (4) were both prepared in a 4% overall yield in six steps based on (Z)-2-penten-1-ol (12).
四种具有6,8-二氧双环[3.2.1]八烷环的外消旋信息素的无保护基合成在五或六个步骤中完成,起始材料为商业可得的(±)-
3-丁炔-2-醇(6)和2-烯烃卤化物或2-烯-1-醇,关键反应为
路易斯酸催化的δ, ε-环氧酮的
缩醛化反应。(±)-正面醇(1)是通过五步从美克
氯(5a)制得,整体产率为25%;(±)-内勃香醇(2)是通过五步从(E)-
2-戊烯基
溴化物(5b)制得,整体产率为23%;(±)-外勃香醇(3)与(±)-3,4-脱氢-外勃香醇(4)均是通过六步从(Z)-
2-戊烯-1-醇(12)制得,整体产率为4%。