Intramolecular Wittig Reaction of α,α′‐Dioxocycloalkylidenetributylphosphoranes: Formation and Trapping of Cycloalkyn‐2‐ones with Five‐and Six‐Membered Rings.

Reaction of the title phosphoranes with homophthalic anhydride or 1,3-diphenylisobenzofuran in the presence of Me3SiCl gave the corresponding Diels–Alder adducts, indicating the transient intermediacy of cycloalkyn-2-ones with five- and six-membered rings.