Exploring the Reactivity of (E)-3(5)-(2-Hydroxyphenyl)-5(3)-styryl-1H-pyrazoles as Dienes in the Diels–Alder Reaction: A New Synthesis of 1H-Indazoles

Abstract

The reactivity of ( E )-3(5)-(2-hydroxyphenyl)-5(3)-styryl-1 H -pyrazoles as dienes in the Diels–Alder cycloaddition reaction was investigated. It is shown that di-tosylated derivatives react with N -methylmaleimide under microwave irradiation to afford the corresponding endo -tetrahydroindazoles, except in the case of strong electron-withdrawing substituents. Dehydrogenation of these tetrahydroindazoles with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) gave the expected 1 H -indazoles in low to good yields.