Anthrone (1) reacted in pyridine/piperidine with 3,5-dimethoxybenzaldehyde (2) to give 10-(3,5-dimethoxybenzylidene)-9-anthrone (3). Catalytic hydrogenation (5% Pd on carbon) of 3 afforded 10-(3,5-dimethoxybenzyl)-9-anthrone (4). 10-(3,5-Dimethoxybenzyl)-10-(3-methoxybenzyl)-9-anthrone (6) was obtained by alkylation of anthrone 4 with 3-methoxybenzyl chloride (5). Subsequent reduction of 6 with NaBH₄ gave 10-(3,5-dimethoxybenzyl)-10-(3-methoxybenzyl)-9(10H)-9-anthranol 7. 7 exhibits in the presence of formic acid or p-methylphenyl-sulfonic acid a selective 1,7-elimination of water which leads to homotriptycene (8). It could be assumed that the protonation of the hydroxy group leads to a carbenium ion intermediate which selectively attacks as electrophile the electron-rich benzene ring with 3,5-dimethoxy groups, instead of attacking the benzene ring with 3-methoxy group.

Key words: anthranol, condensation, triptycene, electrophilic substitution