Camphor-10-sulfonic acid catalyzed condensation of 2-naphthol with aromatic/aliphatic aldehydes to 14-aryl/alkyl-14H-dibenzo[a,j]xanthenes

The (+/-)-camphor-10-sulfonic acid (CSA) catalyzed condensation of 2-naphthol with both aliphatic/aromatic aldehydes at 80 degrees C yielded 14-alkyl//aryldibenzoxanthenes as the sole products in high yields. However, the same condensation with benzaldehyde at 25 degrees C afforded a mixture of the intermediate 1,1-bis-(2-hydroxynaphthyl)phenylmethane and 14-phenyldibenzoxanthene, while the condensation with aliphatic aldehydes at 25 degrees C furnished the corresponding 14-alkyldibenzoxanthenes as the sole products. Moreover, the condensation of 2-naphthol with aromatic/aliphatic aldehydes with low catalyst loading (2 mol %) was greatly accelerated under microwave irradiation to afford the corresponding 14-aryl/alkyldibenzoxanthenes as the sole products in high yields.