In continuation of the authors' earlier work on substances having a carbonyl bridge, it has been found that tetraphenylcyclopentadienone can be used as one of the components in the diene synthesis. Products are described resulting from the addition of maleic anhydride, maleic, fumaric, and acetylene dicarboxylic esters, and benzoyl phenylacetylene. In some instances the primary addition products containing a carbonyl bridge could be isolated. Tetraphenylbenzene derivatives result from secondary reactions. Benzalacetophenone, dibenzoyl-ethylene and diphenylketene did not add to tetraphenylcyclopentadienone.In the previously described reaction between maleic anhydride and anhydroacetonebenzil, certain intermediates have been isolated, confirming the mechanism suggested to account for the formation of a dianhydride.