Unusual ring transformation of 2-halogeno-N-phenacylpyridinium salts in reaction with secondary amines: a facile 'one-pot' route to 1-amino-4-(oxazol-2-yl)butadienes

摘要

2-Halogeno-N-phenacylpyridinium salts 1 (Hal=Cl, Ar=p-NO_2Ph; Hal=Br, Ar=Ph) in reaction with aliphatic secondary amines undergo an unusual ring transformation to 1-amino-4-(5-aryloxazol-2-yl)buta-1, 3-dienes 9 and 10. The configuration of the products (1E, 3E or 1E, 3Z) depends on the reaction temperature. A suggested mechanism for the transformation involves intermediate formation of 2-aryloxazolo[3, 2-a]pyridinium salt 4.