Mild synthesis of fused polycyclic 1,6-naphthyridin-4-amines and their optical properties

A mild and straightforward synthetic route to tri-, tetra-, and pentacyclic 1,6-naphthyridin-4-amines is presented. The protocol involves CF3SO3H- or H2SO4-mediated Friedel-Crafts-type intramolecular cycloaromatisation of 4-(arylamino)nicotinonitriles in which the cyano group acts as a one-carbon synthon. The transformation achieves good to excellent yields and can be performed on a gram scale. Additionally, the exploration of fluorescence properties of these compounds demonstrates their potential application as fluorophores.