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■ Reactions of Ethyl 2-Hydroxy-4-(4-hydroxy-6-methyl-2-pyron-3-yl)-4-oxo-2-butenoate with N-Nucleophiles. Synthesis of Isomeric Pyronylpyrazoles and Pyrano[4,3-c]pyrazoles

Ana Brbot-Saranovic,* Branka Katusin-Razem, and Ivana Susnik

*Institute "Ruder Boskovic", University of Zagreb, 411000 Zagreb, Croatia

Abstract

Reaction of the title compound 1 with aniline gave two Schiff’s bases 2 and 3, while condensation of 1 with phenylhydrazine afforded four products 4 - 7. Compounds 4 and 6 were formed after initial nucleophilic attack at the central carbonyl carbon of tricarbonylic moiety, while 5 and 7 were formed after initial attack at the 4-position of the 2-pyrone ring. These structures were confirmed by the selective preparation of 4 - 7 from pyranopyrandiones 12 and 13, respectively. Pyrazole-4-carboxylic acid derivatives 6 and 7 cyclize in acetic anhydride into fused pyrano[4,3-c]pyrazoles 8 and 9, respectively. Their structures were compared with that of the parent 3-methyl congeners 14 and 15, obtained from dehydraacetic acid.