Synthesis of pyrrolo[3,2-f]quinolines via reaction of 2,5-dimethyl- or 1,2,5-trimethyl-6-aminoindoles with β-ketoesters

Abstract

The reaction of 2,5-dimethyl- or 1,2,5-trimethyl-6-aminoindoles with β-ketoesters (methyl and ethyl acetoacetates, diethyl oxaloacetate) was found to proceed chemoselectively via the interaction between an amino group of indole and the carbonyl function of ketoester, leading to the formation of enamines. In contrast to enamines synthesized from similar aminoindoles and β-diketones, enamines obtained from β-ketoesters can easily undergo thermal cyclization, furnishing pyrrolo[3,2-f]quinolines with an angular catenation of rings.