45 光学活性ピクロトキサン型セスキテルペン類の合成研究

概要

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Starting with (-)-carvone (2), synthetic investigation of (+)-tutin (1), a representative picrotoxan sesquiterpene, is described. The key steps in this strategy are the stereospecific construction of an asymmetric C_1 carbon via the Claisen rearrangement of the vinyl ether (10) derived from 4β-hydroxycarvone (8) and the highly stereoselective introduction of β-vicinal diol onto C_2 and C_3 carbons by OsO_4 oxidation of bromo-ether (16). The 4β-hydroxycarvone (8), a key intermediate for the present synthesis, was efficiently derived from the carvone (2) by means of the Michael addition of benzeneselenol followed by the oxidative elimination of the resulting selenide. The Claisen rearrangement of (10) proceeded smoothly to give aldehyde (11) which was then converted to bromo-ether (12) on treatment with NBS. Zinc-copper reduction of bromo-ether (17), oxidation of the resulting alcohol, and carbonation with LiN(SiMe_3)_2 provided keto ester (19) in high yield. Conversion of the diketone (22) derived from (19) to the picrotoxan skeleton (24) was secured by cyclization with pyrrolidine-benzoic acid followed by hydrolysis of the resulting dienamine (23). Further (24) was transformed into (25) in three steps. Thus the highly stereocontrolled synthesis of the picrotoxan skeleton (25) starting with the carvone (2) has been achieved. The transformation of (25) into picrotoxan sesquiterpenes is under way.
天然有機化合物討論会の論文
1983-09-15