The reaction of phenylhydrazine with squaric acid: a model for carbohydrate osazone formation

Abstract

The reaction of squaric acid ( 1) with phenylhydrazine yields cyclobutanetetraone poly(phenylhydrazones) ( 2–4), as reported earlier, as well as squaric acid derivatives, reported here. The latter products are a salt, 1,3-dianilinocyclobutenediylium-2,4-diolate ( 5), and 1-anilino-2-phenylhydrazinocyclobutene-3,4-dione ( 6), which upon oxidation yields tautomeric forms of cyclobutanetetraone 1-anilide-2-phenylhydrazone ( 7a and 7b). The structure of the compounds isolated was established by 1H, 13C, 2D COSY, and 2D J-resolved NMR spectroscopy. The similarity between the reaction of squaric acid ( 1) with phenylhydrazine and osazone formation can be seen from the analogy between compounds 2, 6, and 7b and intermediates produced during carbohydrate osazone formation, as well as from the fact that these compounds afford an osazone analog ( 4) when treated with phenylhydrazine. It was also found that compound 5 can be generated by a retro-osazone reaction when cyclobutanetetraone bis(phenylhydrazone) ( 2) is heated with aniline.