Annulation of 3-[(R)-p-toluenesulfinyl] -2-oxopropylidenetriphenyl-phosphorane with 1,4-enediones; Highly enantioselective synthesis of cyclopentenones

3-[(R)-p-Toluenesulfinyl]-2-oxopropylidenetriphenyl-phosphorane reacted with 1,4-enediones in the presence of BuLi to give (4S,5R)-4-acylmethyl-5-[(R)-p-toluenesulfinylcyclopent-2-enones in a highly diastereoselective fashion. Subsequent desulfurization of the cyclization products furnished highly enantiomerically enriched (S)-4-acylmethylcyclopent-2-enones.