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

Abstract

2-Halogeno-N-phenacylpyridinium salts 1 (Hal = Cl, Ar = p-NO₂Ph; 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.