The synthesis and physical properties of some 2-alkylthio-4-oxoquinoline-3-carboxylate esters

Abstract

Anilino(alkylthio)malonates, readily available by alkylation of the anions formed by the addition of malonate ions to isothiocyanates, have been found to undergo smooth cyclisation, upon being heated in o-dichlorobenzene, to give the title compounds in moderate to good yields. In certain cases the compounds so prepared may be isolated in the 4-quinolinol or 4-quinolone forms, this tautomeric behaviour depending on factors which include the solvent of crystallisation, the temperature of the sample, and the steric bulk of the 2-alkylthio-substituent. In solution this tautomerism has been studied spectroscopically, and in the solid state by means of differential-scanning calorimetry. Certain unusual features in the spectroscopy of these compounds are discussed.