Preparation of benzo[c][2,7]naphthyridin-5(1H)-ones as analogs of benzopyrano[3,4-c]pyridin-5-one bronchodilators

A series of 2,3,4,6-tetrahydro-8,9-dimethoxybenzo[c][2,7]naphthyridin-5(1H)-ones was prepared as potential anticholinergic bronchodilators. The naphthyridine ring system was constructed by cyclization of a 3-amido-4-piperidone. Alkylation with alkylaminoethyl chlorides or reductive amination of an intermediate methyl ketone yielded the final target compounds.