An efficient synthesis of benzo[b][1,8]naphthyridine-3-carboxylic methyl esters

Methyl-3-(2-chloroquinolin-3-yl)acrylates 5a-i on reaction with methyl amine in acetonitrile yielded methyl-3-[2-(methylamino)quinolin-3-yl]acrylates 6a-i. When, these were followed by the reaction with the Vilsmeier reagent, they afforded methyl benzo[b][1,8]naphthyridin-3-carboxylate 7a-i in good yields.