2,2-Disubstituted-1,2-dihydro-3H-indol-3-ones by base- and thermal-induced cyclisations of o-azidophenyl s-alkyl ketones and o-azidobenzoyl esters

Abstract

o-Azidophenyl s-alkyl ketones in ethanolic potassium hydroxide at room temperature undergo loss of nitrogen and cyclisation to 2,2-dialkyl-1,2-dihydro-3H-indol-3-ones in high yield. Kinetic data (E_act. 62.4 and 71.6 kJ mol^–1, respectively) obtained for the o-azidophenylisopropyl and o-azidophenylcyclohexyl ketones support an assisted nitrogen loss from the azide via the enolate ion, rather than a nitrene reaction. 1,2-Dihydro-3H-indol-3-ones, along with in some cases 2,1-benzisoxazoles, have also been obtained by the thermolysis and spray vacuum pyrolysis of other o-azidophenyl alkyl ketones, diethyl o-azidobenzoyl malonate, and ethyl o-azidobenzoyl(phenyl)acetate.