[Untitled]

The examples reported for the recyclization of 3-acylaminobenzo[c]pyrilium salts are limited to their reactions with ammonia [1] and ortho-phenylenediamine [2], although the structure of these compounds would lead us to expect a great variety of transformations. In a study of 3-acylaminobenzo[c]pyrilium salts with nitrogen-containing nucleophiles, we assumed that the formation of 1,3-aminonaphthol derivatives would be possible in their reactions with amines as in the case of 5-alkyl-2-oxobenzo[c]pyrrolo[3,2-e]pyrilium perchlorates [3]. The structure of the products of the reactions of 3-acylamino-1-alkylbenzo[c]pyrilium salts (1) with benzylamine was found to depend on the length of the alkyl substituent at C(1) in the benzo[c]pyrilium cation. Heating 3-acetylamino-6,7-dimethoxy-1-methylbenzo[c]pyrilium perchlorate (1a) with two equivalents of benzylamine gives 3-acetylamino-1-benzylamino-6,7-dimethoxynaphthalene (2), whose structure and composition were indicated by IR and H NMR spectroscopy and elemental analysis. Under the same conditions, salt 1b is converted into the "normal" product, aminonaphthol 3. Recyclization with retention of the acetylamino group was quite unexpected since the reported reactions of 1-acylaminobenzo[c]pyrilium cations feature either loss of the acylamino group [1, 2] or participation of this group in intramolecular recyclization to give 3-hydroxyisoquinoline derivatives [4].