Stereochemical studies. XLVII. Asymmetric reduction of 2-alkyl-1,3,4-cyclopentanetriones with lithium aluminum hydride decomposed by optically active .BETA.-aminoalcohols. Syntheses of optically active allethrolone and prostaglandin E1.
作者:MUTSUYOSHI KITAMOTO、KAZUYA KAMEO、SHIRO TERASHIMA、SHUNICHI YAMADA
DOI:10.1248/cpb.25.1273
日期:——
Asymmetric reduction of several kinds of 2-alkyl-1, 3, 4-cyclopentanetriones (1) by the use of lithium aluminum hydride (LAH) partially decomposed by optically active β-aminoalcohols (7), was studied. It was found that the reduction of 2-propyl derivative (1c) with LAH decomposed by 3.0 eq. of (-)-N-methylephedrine (7a), in THF at -70°for 3 hr, followed by acetylation, gave (R)(-)-4-acetoxy-2-propyl-1, 3-cyclopentanedione ((R) (-)-3c), 58% e.e., in 42% yield. When the same reduction procedure was applied to 2-allyl derivative (1b), (R) (-)-4-acetoxy-2-allyl derivative ((R) (-)-3b), 55% e.e., was obtained in 48% yield. Recrystallization of (R)(-)-3b from ether could improve the optical purity up to 97% e.e. The absolute configuration and optical purity of (R) (-)-3b and (R) (-)-3c were established by the chemical correlation with (R) (-)-allethrolone ((R) (-)-5). When 2-(6-carbomethoxyhexyl)-1, 3, 4-cyclopentanetrione (1a) was treated by the exploited reduction condition, the corresponding (R) (+)-alcohol ((R) (+)-2a), 54±6% e.e., from which PGE1 had been synthesized, was prepared in 58% yield.
研究人员利用部分被光学活性 β-氨基醇(7)分解的氢化铝锂(LAH)对几种 2-烷基-1,3,4-环戊四酮(1)进行了不对称还原。研究发现,用 3.0 eq. (-)-N-methylephedrine (7a)分解的 LAH 在 THF 中于 -70° 下还原 2-丙基衍生物 (1c) 3 小时,然后进行乙酰化,可得到(R)(-)-4-乙酰氧基-2-丙基-1, 3-环戊二酮 ((R)(-)-3c),纯度为 58%,产率为 42%。当对 2-烯丙基衍生物(1b)采用同样的还原程序时,得到了(R) (-)-4- 乙酰氧基-2-烯丙基衍生物((R) (-)-3b ),纯度为 55%,收率为 48%。通过与(R) (-)-allethrolone ((R) (-)-5) 的化学相关性,确定了(R) (-)-3b 和(R) (-)-3c 的绝对构型和光学纯度。用所利用的还原条件处理 2-(6-羰基甲氧基己基)-1,3,4-环戊四酮 (1a),制备出相应的(R) (+)-2a 醇 ((R)(+)-2a),产率为 58%,其中 54±6% 的 PGE1 是由其合成的。