Reacting Cyclopropenones with Arynes: Access to Spirocyclic Xanthene–Cyclopropene Motifs

A formal insertion of two aryne moieties
into the carbon–oxygen
double bond of cyclopropenone has been realized. Spirocyclic xanthene–cyclopropene
scaffolds were obtained. Mechanistically, a sequence of a formal [2
+ 2]-cycloaddition followed by electrocyclic ring opening and a terminating
[4 + 2]-type cycloaddition is postulated. The use of an electron-rich
aryne precursor led to ring cleavage of the cyclopropene to afford
an unprecedented xanthylium salt.