利用Sharpless不对称双羟基化反应制备光学活性的偶姻类化合物

以相应的酮为起始原料,通过烯醇硅醚的中间体,利用Sharpless不对称双羟基化反应制备了5个光学活性的偶姻化合物。4-庚酮、5-壬酮、2,6-二甲基-4-庚酮、5-甲基-3-己酮和4-苯基-2-丁酮在不同碱的作用下与三甲基氯硅烷或三甲基碘硅烷反应得到动力学控制或热力学稳定的烯醇硅醚后,再进行Sharpless不对称双羟基化反应,除5-甲基-3-己酮的烯醇硅醚外,其他烯醇硅醚用AD-mix-α氧化得到S构型的偶姻产物,对映体过量值(ee值)在62%以上,用AD-mix-β氧化得到R构型的偶姻产物,ee值在75%以上。5-甲基-3-己酮的烯醇硅醚分别用AD-mix-α和AD-mix-β氧化都得到R构型的2-羟基-5-甲基-3-己酮,前者ee值只有16%,后者ee值为76%;用D-果糖和L-果糖衍生的史一安催化剂和过硫酸氢钾氧化,则分别得到R构型和S构型产物,ee值分别为75%和73%。

Preparation of Optically Active Acyloins by Sharpless Asymmetric Dihydroxylation

Five optically active acyloins were prepared by Sharpless dihydroxylation of silyl enol ethers as intermediates starting from the corresponding ketones.4-Heptanone,5-nonanone,2,6-dimethyl-4-heptanone,5-methyl-3-hexanone and 4-phenyl-2-butanone reacted with Me3SiCl or Me3SiI in the presence of different bases to give a kinetically controlled or thermally stable silyl enol ether.The obtained silyl enol ethers were oxidized through Sharpless asymmetric dihydroxylation using AD-mix-α or AD-mix-β to give(S)-acyloins in >62% ee or(R)-acyloins in >75% ee respectively except the silyl enol ether derived from 5-methyl-3-hexanone.This silyl enol ether was oxidized by either AD-mix-α or AD-mix-β to give(R)-acyloin.AD-mix-α gave a 16% ee while AD-mix-β gave a 76% ee.However,the silyl enol ether was oxidized by oxone and Shi′s catalyst derived from D-or L-fructose to give(R)-acyloin in a 75% ee and(S)-acyloin in a 73% ee respectively.