Oxazolium salts amines

The oxazole ring possesses less aromatic stabilization than a thiazole ring and is readily opened in many of its fused derivatives, especially in oxazolium salts. In the pyridazinium derivative (191) the oxazole ring is opened by oxygen, sulfur or carbon nucleophilic attack at the C-8a ring junction (77YZ422). In the mesoionic pyridine (192) an amine attacks at C-2, which is a pseudocarbonyl carbon atom (70JCS(C)1485). 

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