P-5 フェネチルアミンを用いる数種の苔類セスキテルペンのキラル合成 : キラル反応生成物の絶対配置とCDスペクトル(ポスター発表の部)

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Imines of substituted cyclohexanone derivatives with (S)-(-)-1-phenylethylamine were reacted with methyl acrylate or methyl propiolate to yield optically active cyclohexanone derivatives after hydrolysis in good to excellent yield with good e.e. The absolute configurations of these products can not be determined by only measuring the CD spectra, because these molecules adopt conformations different from what expected in general. We have prepared differently substituted cyclohexanone derivatives and established the absolute configurations of some of the derivatives with chiral auxiliary by X-ray crystallography. All the absolute configuration of the product derived from the same phenylethylamine was same. The substituent with long carbon side chain did not enter the area of the front octant of the carbonyl group. The sign of the Cotton effect mainly depended upon the conformation of cyclohexanone ring which was regulated by the substitution pattern. The global minimum conformation of methyl (1-methyl-2-oxocyclohexyl) propionate 2 was calculated by MM2 using CONFLEX. More than 96% of the preferred conformation was that the C-3 side chain was in the axial position. In the case of methyl (1-ethyl-2-oxocyclohexyl) propionate 23, 56% had the axial side chain and 44% equatorial. These results also support the CD data as shown in Table 1. These reaction products were applied to the synthesis of the optically active sesquiterpenoids isolated from liverworts in order to establish the absolute configurations of these terpenoids. So far, tridensone 26, riccardiphenols A (31) and B (32) were synthesized and the work toward trifarienols A (36a) and B (36b) are under way.
1995-09-01

P-5 フェネチルアミンを用いる数種の苔類セスキテルペンのキラル合成 : キラル反応生成物の絶対配置とCDスペクトル(ポスター発表の部)

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