Studies on the synthesis of aminoquinoline derivatives. VII. Synthesis of imidazo(1,2-alpha)quinoline derivatives

Abstract

Nucleophilic reaction of the methyl derivatives of 2-chloroquinoline with aminoethanol, ε-aminocaproic acid, and its ester was examined. ε-Aminocaproic ester was extremely difficult to react, aminoethanol reacted with better yield than 3-aminopropanol, and reaction with ε-aminocaproic acid failed to give any reaction product. The hydroxyl group in ω-position of 2-(2-hydroxyethylamino) quinoline, obtained by reaction with aminoethanol, was chlorinated to obtain the methyl derivative of 2-(2-chloroethylamino)-quinoline hydrochloride. Neutralization of this hydrochloride by addition of saturated sodium hydrogencarbonate solution to pH 7.0-7.1 afforded some crystals which were found to be not the liberated base but 2, 3-dihydro-1H-imidazo [1, 2-α] quinolinium chloride, produced by the new formation of a five-membered ring between the chlorinated carbon atom and the non-conjugated electron pairs in the sp orbital of the ring nitrogen during neutralization. This quaternary salt was heated with 10% sodium hydroxide solution and a pseudo base possessing a hydroxyl in 3a-position was obtained.