Pyrolysis of 3-hydroxy-2-arylhydrazonoalkanoic acid derivatives

1,2-Diaza-1,3-butadienes have been obtained from readily available 3-hydroxy-2-arylhydrazonopropanoates under various reaction conditions including pyrolysis, dehydration under Mitsunobu conditions or with acetic anhydride or acetic acid. According to their method of synthesis these 1,2-diaza-1,3-butadienes underwent subsequent reactions to give interesting products, and in the presence of proper dienophiles gave the corresponding cycloaddition products. Also, a new approach to pyrazole-3-carboxylic acid derivatives was discovered during an attempt to dehydrate 3-hydroxy-2-arylhydrazonobutanoic esters.