Preparation of Chiral, Highly Functionalized Cyclopentenones

During a detailed examination on the cyclization of 1, 4-diketones to cyclopentenones, we have found that two oxygenated products (4 and 5) are formed when the purification by column chromatography on silica gel takes a long time. The highly functionalized cyclopentenone (4a) obtained as the major product in this manner seems to be an attractive synthon for the synthesis of natural products. For eaxmple, the chiral synthon (1S, 4S)-4-benzyloxycarbonyl-1, 4-dihydroxy-2-methoxycarbonyl-3-methyl-2-cyclopentene ((+)-7) with high optical purity was obtained by microbial reduction with Rhodotorula rubra CCY 20-7-1, and the absolute stereochemistry was established independently by using the exciton chirality method and the chemical method.