The conjugate addition–Peterson olefination reaction for the preparation of cross-conjugated cyclopentenone, PPAR-γ ligands

5-Alkylidenecyclopent-2-enones 15a-q may be prepared via a conjugate addition-Peterson olefination sequence, best achieved in one-pot, using exo-2-trimethylsilyl-3a,4,7,7a-tetrahydro-4,7-methanoinden-1-one 12, followed by a retro-Diels-Alder reaction. The geometry of the exocyclic alkene may be controlled according to the use of organometallic species in the conjugate addition step; organocuprate reagents are found to selectively lead to the formation of E-exocyclic alkene adducts, whereas Grignard reagents favour the formation of Z-alkenyl isomers. The use of enantiomerically enriched 12, accessed from an asymmetric Pauson-Khand reaction, affords the corresponding enantioenriched 5-alkylidenecyclopent-2-enones and this approach is exemplified by the short, stereoselective total syntheses of two cyclopentenone phytoprostanes 51 and 13,14-dehydrophytoprostane J1 65. The ability of this family of synthetic compounds to activate the peroxisome proliferator activated receptor-gamma is reported.