Chiral Preparation of Polyoxygenated Cyclopentanoids

A series of polyoxygenated cyclopentanoids, including 2,2-dimethyl-3a,6a-dihydro-4H-cyclopenta[d][1,3]dioxol-4-one, has been prepared in both enantiomeric forms from cyclopentadiene by employing lipase-mediated kinetic resolution as the key step. Thus, cyclopentadiene is first transformed into racemic cis-4-cumyloxycyclopent-2-en-1-ol which is resolved under transesterification conditions in the presence of lipase PS. After transformation into the corresponding tert-butyldimethylsilyl (TBS) ethers, each of the enantiomers is cis-dihydroxylated diastereoselectively from the less hindered face which is transformed into the 2,3-O-isopropylidene-1,4-di-O-protected (trans-1,2 : cis-2,3 : trans-3,4)-1,2,3,4-cyclopentanetetraol. Selective removal of the 1,4-protecting group gives the corresponding 2,3,4-O-protected cyclopentanols which are further transformed into the 2,3,4-O-protected cyclopentanones on oxidation without suffering β-elimination. Exposure of the cyclopentanones to warm acetic acid allows β-elimination to give rise to the dehydration product 2,2-dimethyl-3a,6a-dihydro-4H-cyclopenta[d][1,3]dioxol-4-one having the corresponding chirality without losing their original chiral integrity.

lipase-mediated kinetic resolution - enantiodivergent synthesis - enantioconvergent synthesis - chiral building block - polyoxygenated cyclopentanoids - oxidations - osmium