A stereoselective synthesis of a dihydrofuran derivative (5) and an allylhalide (8), possible precursors of the cembranes (-)-sarcophytonin A and (-)-sarcophytoxide, is described. The optically active dihydrofuran, right half, segment (49) was synthesized starting from a naturally occurring monoterpene, (-)-carvone. It was converted into the phenylselenide (14) via three steps. Oxidation of 14 with m-chloroperbenzoic acid and then treatment with pyridine yielded the epoxy olefin (29). Cleavage of the epoxide with boron trifluoride etherate gave the methoxy alcohol (31). Bromoetherification with N-bromosuccinimide selectively yielded the cis-hexahydro-1-oxaindan derivative (36) having a new chirality at the C-6 position. Reductive debromination of 36 followed by oxidation and then enol silylation yielded the less substituted silyl enol ether (39). Ozonolysis of 39 followed by methylation and elimination of methanol with potassium tert-butoxide and then reduction with 9-borabicyclo[3.3.1]nonane (9-BBN) gave the dihydrofuran derivative (41). Protection as the silyl ether (42) and phenylselenenylation and then treatment with hydrogen peroxide yielded the unsaturated ester (45). Reduction followed by thiophenylation of the resulting hydroxyl group afforded the dihydrofuran derivative (49) as a right half segment. Left half segments, the chloride (53) and the bromide (54), were synthesized starting from geraniol via several steps.
描述了一种立体选择性合成二氢
呋喃衍
生物(5)和烯丙基卤化物(8),这可能是香榧素(-)-sarcophytonin A和(-)-sarcophytoxide的前体。光学活性的二氢
呋喃,右半部分片段(49)是从一种天然存在的单萜,(-)-
香叶醇合成而来的。它通过三个步骤转化为苯基
硒化物(14)。使用对
氯过
苯甲酸对14进行氧化,然后用
吡啶处理,得到环氧烯烃(29)。用
三氟化硼醚化物切割
环氧化物,得到甲氧醇(31)。使用N-
溴马来
酰亚胺进行
溴醚化反应,选择性地得到具有C-6位置新手性的顺式六氢-1-氧烷衍
生物(36)。对36进行还原脱
溴反应,随后氧化和烯醇
硅烷化,得到取代较少的
硅烯醇醚(39)。对39进行
臭氧化,随后甲基化和用
氯化钾-
叔丁醇消除
甲醇,最后用9-
硼双环[3.3.1]诺烷(9-BBN)还原,得到二氢
呋喃衍
生物(41)。保护为
硅醚(42),然后进行苯基
硒化反应,再用
过氧化氢处理,得到不饱和酯(45)。对得到的羟基进行还原,然后进行
噻吩基化,获得右半部分的二氢
呋喃衍
生物(49)。左半部分片段,
氯化物(53)和
溴化物(54),则是从柑橘醇出发合成的,经过几个步骤。