3-Aryl- and 2,3-Diaryl-4-oxo-4,5,6,7-tetrahydroindazoles. 1. Reactions of Phenyl- and Tosylhydrazones of Dimedone and Cyclohexane-1,3-dione with Substituted Benzaldehydes

Abstract

Keywords: 3-aryl-and 2,3-diaryl-4-oxo-4,5,6,7-tetrahydroindazoles, substituted benzaldehydes, phenyland tosylhydrazones of cyclohexane-1,3-diones.In continuation of studies on the modification of hydrogenated indazoles and quinazolines, mainly in their carbocyclic structural fragment [1-5], we have turned to the synthesis of 3-aryl-4-oxo-4,5,6,7-tetrahydroindazoles. Two schemes are known for their synthesis. One is the interaction of enehydrazines, obtained from cyclohexane-1,3-diones and benzenesulfonic acid hydrazide, with aromatic aldehydes [6], and the other is the interaction of 2-benzoylcyclohexane-1,3-diones with hydrazines [7]. 2,3-Diaryl-4-oxo-4,5,6,7-tetrahydroindazoles are obtained by the interaction of phenylhydrazones of cyclohexane-1,3-diones with aromatic aldehydes [8] and by the reaction of 2,3-diphenyl-1,3,4-oxadiazolium perchlorate with dimedone [9].We selected the reaction of 3-enehydrazino-2-cyclohexen-1-ones with aromatic aldehydes for the synthesis of 3-aryl-and 2,3-diaryl-4-oxo-4,5,6,7-tetrahydroindazoles [6,8]. Such a selection was made, in spite of the extremely large number of known 2-aroylcyclohexane-1,3-diones [10-13] many of which are herbicides, because of the simplicity of the synthesis and the availability of a wide selection of aldehydes.In the present work 16 new 2,3-diaryl-4-oxo-4,5,6,7-tetrahydroindazoles 6 were synthesized by the reaction of phenylhydrazones of dimedone 2,3A and cyclohexane-1,3-dione 2,3B with substituted benzaldehydes 4.It was shown previously [8] that on boiling the reactants in alcohol for 15 min pyrazolines of type 5 are formed predominantly with only a little of their dehydrogenation products 6. However the procedure for separating these compounds is complex, and in addition pyrazolines 5 are unstable. We selected more rigid reaction conditions, heating a solution of equimolar quantities of reactants in DMSO at 100°C for 3-4 h, which leads to the formation of compounds 6 exclusively (Table 1).