Dehydration of 2-(2-arylethyl)-2-hydroxy-4-oxopentanoic acids and their hydrazones to form heterocycles

Article abstract of DOI:10.1002/prac.19973390104

Dehydration of 2-(2-arylethyl)-2-hydroxy-4-oxopentanoic acids 1 with hydrochloric acid/acetic acid, affords 3-(2-arylethyl)-5-hydroxy-5-methyl-2(5H)-furanones4. Compounds of type 1 and 4 represent suitable precursors for the formation of pyridazin-3-ones 7 as they smoothly react with hydrazine. A new series of s-triazolo[4,3-b]pyridazin-3-ones 12 and tetrazolo[1,5-b]pyridazines 15 are obtained from the 3-chloropyridazines 11 upon treatment with semicarbazide and sodium azide, respectively. Reaction of 11 with phenyl- acetyl-hydrazine provides 3-benzyl-6-phenyl-8-(2-phenyl- ethyl)-s-triazolo[4,3-b]pyridazine 13 via dehydrative cyclization of the intermediate 14 which was clarified to exhibit tautomeric equilibria between enol-hydrazine form A and keto-hydrazine form B by means of ¹H and ¹³C NMR spectroscopy. Attempts to synthesize 3-alloxy-pyridazines 18 by reacting 11 with sodium alloxide afford N-allyl compounds 17. Johann Ambrosius Barth 1997.