Acid-Catalyzed Cyclization of Anthracenol Derivatives to Homotriptycenes

10-Benzyl-9,10-dihydroanthracen-9-ols, having high electron densities in the benzene ring, exhibit in the presence of acid a transannular ring closure to the corresponding homotriptycenes in almost quantitative yields. Since the starting compounds are easily accessible from 9(10H)-anthracenone, this process represents the most facile route to such pentacyclic systems. An electron-releasing methoxy group enables the intramolecular electrophilic substitution in its para position. In the absence of such an activation, a number of alternative processes can occur, namely the acid-catalyzed dehydration to anthracene derivatives with (R ≠ H) or without (R = H) rearrangement or a disproportionation reaction of the secondary alcohol to the corresponding ketone and hydrocarbon.