A procedure for the preparation of dl-dehydrofukinone (1), an eremophilane type sesquiterpene, from the diene adducts (3), prepared from the reaction of 4-methyl-3-methoxycarbonyl-2-cyclohexen-1-one with butadiene, is described. Acetalization-reduction (LiAlH4) of 3 followed by treatment of the corresponding mesylate with base provided 5,6-cis-5-methyltricyclo[4.4.1.01,6]undec-8-en-2-one (7) in 69% overall yields. Reductive cleavage of 7 with lithium metal afforded trans-4β,4aβ-dimethyl-Δ6,7-octalin-1-one (8), bearing a set of vicinal cis two methyl groups on the C-4 and C-4a carbons in an 83% yield. Functionalization of the double bond of 8 involves (1) reduction of carbonyl group and following tetrahydropyranylation, (2) epoxidation followed by regiospecific reduction of the oxirane ring at the C-6 position, and (3) subsequent oxidation of the hydroxyl group, giving trans-4aβ,5β-dimethyl-8β-tetrahydropyranyloxydecalin-2-one (14b) in good yields. The conversion of 14b into the desired 1 was achieved smoothly by (1) hydrolysis of tetrahydropyranyl ether, (2) pyrolysis of its mesylate, and (3) subsequent aldol reaction with acetone followed with dehydration and isomerization of the double bond.
本文描述了一种从 4-甲基-3-甲氧羰基-
2-环己烯-1-酮与
丁二烯反应制备的二烯加合物(3)中制备 dl-脱氢紫杉酮(1)(一种 eremophilane 型
倍半萜)的方法。先对 3 进行
乙缩醛化还原(LiAlH4),然后用碱处理相应的
甲磺酸盐,最后得到 5,6-顺式-5-甲基
三环[4.4.1.01,6]十一碳-8-烯-2-酮(7),总产率为 69%。用
金属
锂对 7 进行还原裂解,得到了反式-4β,4aβ-二甲基-Δ6,7-
辛烯-1-酮(8),该化合物在 C-4 和 C-4a 碳上带有一组邻接的顺式两个甲基,收率为 83%。8 双键的官能化过程包括:(1) 还原羰基,然后进行
四氢吡喃化;(2) 环氧化,然后在 C-6 位进行
环氧乙烷环的区域特异性还原;(3) 随后氧化羟基,得到反式-4aβ,5β-二甲基-8β-
四氢吡喃氧基
萘-2-酮(14b),收率很高。通过 (1)
四氢吡喃基醚的
水解,(2) 其
甲磺酸盐的热解,(3) 随后与
丙酮的醛醇反应,以及双键的脱
水和异构化,可以顺利地将 14b 转化为所需的 1。