In the synthesis of natural products consisting of the basic structure of cyclopentane ring, variously functionalized cyclopentanones are required as starting materials. Previously, we succeeded in a simple, highly stereospecific synthesis of the cis-3,4-disubstituted cyclopentanones by the mild reaction with RhCl(PPh_3)_3. By the application of this newer cyclization reaction, we have succeeded in the synthesis of cis,cis-dihydronepetalactone, prostanoic acid, 8-isoprostanoic acid, (+)-brefeldin A and carbacyclin in the optically active form from limonene or Corey lactone. These compounds were synthesized via the following key steps. 1) 3-(3-Oxobutyl)cyclopentanone was easily converted to the deconjugated bicyclic enone (3→4). 2) The regioselective alkylation of limonene was performed by using s-BuLi-TMEDA (1→8). 3) The cis-3,4-disubstituted cyclopentanone from limonen-10-ol could be converted to the trans-3,4-disubstituted cyclo-pentanone by the epimerization (15→16, 22→23).
