Abnormal Nazarov Reaction. A New Synthetic Approach to 2,3-Disubstituted 2-Cyclopentenones

Acid-catalyzed reaction of β,β′-disubstituted cross conjugated dienones or the corresponding ethylene acetals gives mainly 2,3-disubstituted 2-cyclopentenones in stead of the simple Nazarov cyclization products, 3,4-disubstituted 2-cyclopentenones. This transformation is explained in terms of electrocyclic ring-closure, addition of hydroxylic solvent(s), tautomerization of the resulting 2-hydroxycyclopentanone intermediates, followed by solvolysis and isomerization. Based on this working hypothesis a new route to jasmonoids is disclosed which involves acid-treatment of the acyloin disilyl ethers derived from substituted glutarates.