RING TRANSFORMATIONS OF HETEROCYCLIC-COMPOUNDS .1. 2-AMINO-BENZOPHENONES AND 7-OXO-HEPTA-2,4-DIENENITRILES BY REACTION OF 2,4,6-TRIARYLPYRYLIUM SALTS WITH 4-NITROBENZYL CYANIDE

2,4,6-Triarylpyrylium salts 1 react with 4-nitrobenzyl cyanide in the presence of sodium acetate, triethylamine or triethylamine/acetic acid to give 7-oxo-hepta-2,4-dienenitriles 2. With stronger bases such as sodium methanolate or ethanolate a ring transformation of the salts 1 occurs giving rise to 2-amino-benzophenones 3 which can also be obtained by cyclization of the nitriles 2. Under the same conditions the 3-methyl-2,4,6-triphenylpyrylium salt 4 forms the 4-methyl-7-oxo-hepta-2,4-dienenitrile 5 by regioselective addition of the 4-nitrobenzyl cyanide at C-2 or it is converted to the 2-amino-5-methyl-benzophenone 6. The ring transformation of the pyrylium salts 1/4 by 4-nitrobenzyl cyanide represents a new and simple method for the preparation of 2-amino-benzophenones. - Spectroscopic data of the novel compounds are discussed; the structure of 5 was confirmed by a single crystal X-ray analysis.