Cycloaddition reactions of isonitrosoflavanone esters with Schiff bases and with heteroaromatic rings

Abstract

Isonitrosoflavanone toluene-p-sulphonate reacts with Schiff bases to form (o-hydroxybenzoyl)imidazoles (6); in one case the regioisomeric pyrazole (10) was also isolated. Analogous reactions occur with pyridine and its methyl- and benzo-derivatives to form pyridoimidazoles [cf. (11)].

The chemical identities of (6b), (11 c), and (13) were elucidated by an X-ray diffraction study, although each exhibits some conformational disorder in the crystalline state, associated with a rotation of the hydroxyphenyl moiety. The hydroxy-group can intramolecularly hydrogen-bond with either the carboxylate oxygen atom or the imidazo-moiety nitrogen. In compounds (6b) and (13) the hydroxy-group is primarily H-bonded to the oxygen, and in (11c) to the nitrgen.