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.

Key words: PROLINE, CATALYTIC BEHAVIOUR, REACTION MECHANISM