ACID-INDUCED STEREOSELECTIVE FORMATION OF 3,5-CYCLOHEPTADIEN-1-ONES FROM KETENES AND DIENES

The reaction of ketenes 1a or 1b with diene 2 in the presence of trifl uoromethanesulfonic acid providing the cycloheptadienones 5a and 5b co nstitutes the first example of an acid-induced ketene/diene ''cycloadd ition''. The thermal [2 + 2] cycloadducts, bicyclo[3.2.0]hept-2-en-6-o nes 9, are not intermediates in the acid-catalyzed reaction since they rearrange under acidic conditions to the tetralinone derivatives 10. The acid-catalyzed ''cycloaddition'' was mechanistically investigated and the scope of the reaction explored.