A synthesis of Benzo[c][1,8]naphthyridinones: an exception to the Knorr reaction

Abstract

The reaction of 1-methoxyisoquinolin-3-amine with ethyl acetoacetate, and subsequent ring closure, is reported. Conrad-Limpach synthesis leads to the expected 4(1H)-one. The same isomer is formed under Knorr conditions (hot polyphosphoric acid), while a less acidic medium (hot acetic acid) gives the 2(1H)-one.