Synthesis of 4, 5-Dihydro-N(2)-Phenylindazole from Diversely Substituted Cyclic-β-Keto Esters and Its Structural Analysis

Abstract

To achieve the N-phenyl tetrahydroindazoles, t(3)-aryl-r(2),c(4)-bis(isopropoxycarbonyl)-c(5)-hydroxy-t(5)-methylcyclohexanones were treated with phenylhydrazine. Characterizations reveal the resultant products are respective N-phenyl dihydroindazoles. The reaction has been taken place in regioselctive manner. Plausible mechanism was proposed for the regioselective formation of dihydroindazoles with the phenyl substituent at N(2) position. Dehydration of hydroxyl group at C-6 position results double bond formation at C(6)–C(7). Besides, an investigation about the prior attempts which are unsuccessful for the synthesis of 2-phenylindazoles from a few cylic-β-keto esters has been discussed. Synthesized compounds were characterized by IR, One and Two dimensional NMR spectra. For all the synthesized compounds 7-13, 1H and 13C NMR spectra was recorded. HMBC and HSQC spectra recorded for a representative compound 7. HMBC spectrum also recorded for compound 8. Stereochemistry of the cyclohex-3-ene ring part in the dihydroindazole is in half chair form, where as in tetrahydroindazole, cyclohexane ring part is in normal chair conformation. Key Words: Dihydroindazole, phenylindazole, substituted indazoles, fused heterocycles, one and two dimensional NMR.