A Simple Preparative Synthesis of Isomeric 2-Chloroquinolinecarboxylic Esters

Abstract

A simple two-stage method for the synthesis of isomeric esters of 2-chloroquinoline-5-, 6-, 7-carboxylic acids by successive oxidation and chlorination reactions of methyl quinoline-5-, 6-, 7-carboxylates has been developed. The target compounds have been obtained in acceptable yields using readily available reagents, simple transformations, and purification methods. Quinoline-8-carboxylic acid ester is unreactive under these conditions. The ester of 2-chloroquinoline-8-carboxylic acid has been obtained with an overall yield of 55%, starting from 8-methylquinoline. The multi-stage process is paid off by the fact that several transformations occur in one reaction cycle. All the methods developed can be used for the synthesis of target compounds on a multigram scale. Intermediate 2(1H)-oxoquinoline carboxylates are promising compounds in the synthesis of functionalized and condensed heterocycles.