56(P21) 1,4-ジオキシシクロヘキセノイド型キラル合成素子を活用するポリオキシシクロヘキサン天然物の集約的合成(ポスター発表の部) [in Japanese] 56(P21) Integrated Syntheses of Polyoxygenated Cyclohexanoid Natural Products Using 1,4-Dioxycyclohexenoid Chiral Building Blocks [in Japanese]
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A series of polyoxygenated cyclohexenoid natural products have been synthesized diastereo-and enantio-selectively in an integrated manner starting from either a synthetic equivalent of chiral cyclohexane-2,5-diene-1,4-diol 2 or a synthetic equivalent of chiral 4-hydroxy-2-cyclohexenone 3 obtained from the meso precursor 1. Thus, starting with (+)-2, all diastereomers of conduritols, including natural conduritols, A 14 and (-)-F 23 as well as unnatural conduritols, D 19, (+)-B 28, (-)-E 25, and (+)-C 32, have been synthesized diastereoselectively in an integrated manner on the basis of the inherent convex-face selectivity exerted by the starting material. Moreover, the same inherent stereochemical nature of (+)-2 has been reflected for the diastereocontrolled construction of some naturally occurring cyclohexenethanol derivatives isolated from some medicinal plants, (-)-cleroindicin E 39, (-)-cleroindicin C 40, and (-)-isocleroindicin E 41, to determine their absolute configuration through the common intermediate (+)-38. (+)-38 has also served as the key intermediate for the diastereocontrolled construction of non-chiral natural products rengyoxide 43, rengyol 44, and cleroindicin A 46 having meso structure. One the other hand, the chiral ketone (-)-3 obtained by the catalytic procedure has been found to serve as an appropriate stating material for the integrated construction of (-)-quinic acid 55 and (-)-shikimic acid 59, occurring in both plants and microorganisms, through the common intermediate 51 on the basis of the same stereochemical background as 2. The enantiomeric α-hydroxyketone (+)-48, generated from the enantiomeric ketone (+)-3, has also been found to serve as an appropriate starting material for the construction of the four cyclohexanemethanol dibenzoate natural products, (-)-zeylenol 66, (+)-pipoxide 67, (-)-tonkinenin A 68 and (-)-varigranol G 69. All of these have been synthesized for the first time from (+)-3 on the basis of its inherent stereochemical nature via the common bromo-ether intermediate 61.