Identify the final product (C) in the following reaction sequence.

Step-by-step solution

The starting material is 2,4,6-triphenylbenzoyl chloride. Treatment with anhydrous AlCl ₃ generates an electrophilic acylium ion at the carbonyl carbon. This acylium ion undergoes an intramolecular Friedel-Crafts acylation by attacking the ortho position of one of the adjacent phenyl rings. This cyclization forms a five-membered ring, resulting in a fluorenone derivative as intermediate (A). The original central benzene ring becomes one of the outer rings of the fluorenone core. The fusion occurs at the original ca