Reactions of squaric acid with phenylhydrazine: structure and nuclear magnetic resonance spectroscopy of cyclobutanetetraone poly(phenylhydrazones)

Abstract

The reaction of squaric acid 1 with phenythydrazine affords three Cyclobutanetetraone poly(phenylhydrazones), viz. a tetrakis(phenylhydrazone)3, a tris(phenylhydrazone)4a⇌4b and a 1,3-bis(phenylhydrazone)5. The structure of these compounds has been determined by IR, MS and 1H and 13C NMR spectroscopy, including 2D COSY, and 1H-detected, single- and multiple-bond 2D carbon–proton chemical-shift-correlation techniques. Chemical methods were also used to elucidate the structure of bis(phenylhydrazone)5, including its synthesis and that of its N-methyl-N-phenyl and N,N-diphenyl analogues 8 and 9 from cyclobutanetetraone, and the preparation of a quinoxaline 7 to establish the 1,3-arrangement of substituents.