Transformations of phenylhydrazones of dialkyl 2-oxo-propane-1,3- dicarboxylate and of ethyl acetoacetate in concentrated sulfuric acid

Article abstract of DOI:10.1002/jhet.5570420724

The hydrazones 3a,b, prepared from phenylhydrazine (1) and dialkyl 2-oxopropane-1,3-dicarboxylate (2a,b) were converted in concentrated sulfuric acid at -5 °C into a mixture of alkyl (3-carboxyindol-2-yl)acetates (5a,b), and ethyl (5-ethoxy-1-phenyl-1H-pyrazol-3-yl)acetate 6. The hydrazone 8, prepared from 1 and ethyl acetoacetate (7) was transformed under the same conditions into a mixture of five compounds: ethyl 2-methylindol-3-carboxylate (9), 2-methylindol-3-carboxylic acid (10), 2-methylindol (11), 5-ethoxy-3-methyl-1-phenyl-1H-pyrazole (12), and 3-methyl-1-phenyl-1H-pyrazol-5- one (13).