脯氨酸的双功能催化作用对制备光学活性环型羟酮的机理 研究

2-甲基-2-乙酰乙基-1，3-环戊二酮(1)，在双功能催化剂L-(-)-脯氨酸的作用下，生成(+)-cis-9S-羟基-8S-甲基氢茚-1,5-二酮[(+)-2],化学产率100%，光学纯度93.4%e.e.;而在L-(+)-高脯氨酸的作用下，得到的是(-)-2,产率73%,光学纯度65%e.e..加一方面，3R-(醛丙硫基)-4-硫杂环已酮可差向异构的衍生物(7)分别在D-或L-脯氨酸催化下，所得到的都是呈右旋光性的非对映立体异构的产物(+)-cis-1,8-二硫杂-4R-羟基-9R,10R-十氢萘-5-酮[(+)-8],但从D-脯氨酸得出的光学纯度高得多，这些实验事实和反应机理均可以通过构象分析结合立体结构式得到合理的表达和解释。

Mechanistic study on bifunctional catalysis of prolines in the synthesis of optically active cyclic ketols

It has been found tha under the bifunctional catalysis of L-(-)- proline, 2-methyl-2-acetoethylcyclopentan-1,3-dione (1) cyclized to form (+)-cis- 9S-hydroxy-8S-methylindan-1,5-dione [(+)-2] in 100% chemical yield and 93.4% e.e; while under the catalysis of L-(+)- homoproline, 1 cyclized to form (-) -2 in 73% yield and 65% e.e.. On the other hand, under the catalysis of either D-or L-proline, the epimerizable diastereomer of 3R-(aldehydopropylmercapto) -4- thiacyclohexanone (7) cyclozed to give dextro rotate diastereomeric product (+)-cis-1,8-dithia-4R-hydroxy-9R, 10R-decalin-5- one [(+)-8] in both cases. The catalysis by D-proline was noted to afford much better diastereoselectivity than that by L-prolien. The above experimental results can be rationalized, as proposed in this article, by conformational analysis and by examining the conformation of transition state of the reactions expressed in three dimensional formulas.