P(NMe ₂ ) ₃ -Mediated Umpolung (3 + 2) Annulation of β,γ-Unsaturated α-Keto Carbonyls with p -Quinone Methides: Synthesis of Spirocyclopentenyl p -Dienones

A novel umpolung (3 + 2) annulation reaction between β,γ-unsaturated α-keto carbonyls and p-quinone methides mediated by P(NMe₂)₃ is described, providing a stereoselective approach to the construction of synthetically interesting, densely functionalized spirocyclopentenyl p-dienones. Notably, vinyl-substituted Kukhtin-Ramirez adducts derived from β,γ-unsaturated α-keto carbonyls are employed, for the first time, as three-carbon synthons in (3 + 2)-annulation reaction.