INTRAMOLECULAR 4+3 CYCLOADDITIONS - MODEL STUDIES TOWARD THE SYNTHESIS OF INGENANES

Cyclic oxyallyls derived from 7, 10 and 12-membered ring precursors undergo intramolecular 4+3 cycloaddition with a tethered furan to give polycyclic products. The cycloadduct 7a derived from cycloheptanone possesses the ABC ring structure of the diterpene isoingenol. Those from cyclodecanone and cyclododecanone are tris and pentakis(homo) C ring analogues of 7a and possess the in-out stereochemistry at the B/C ring juncture characteristic of ingenol.