Diprotonation of 5-Acyl-1,2,3,4,5-pentamethylcyclopentadienes

5-Acyl-1,2,3,4,5-pentamethylcyclopentadienes could potentially be protonated on either or both of two sites, the diene moiety in the five-membered ring or the carbonyl oxygen. The protonation of a series of 5-acylpentamethylcyclopentadienes has been examined and evidence is presented which shows that the former site is essentially completely protonated in FSO 3 H and that the carbonyl oxygen is also partially protonated. The extent of …