A comparative study of conventional conditions versus microwave irradiation for the preparation of novel 1,2‐dihydro‐2‐imino‐7‐methyl‐1,6(6H)‐naphthyridin‐5‐ones

The synthesis of novel 1,6‐naphthyridines 6 with potential activity against tuberculosis is described using the reaction sequence 2←4←6. Depending on the ring N‐substitution of the 4‐alkylamino‐6‐methyl‐2(1H)‐pyridones 1 and 2 the electrophilic attack of the Vilsmeier reagent gives rise to the formation of the exocyclic N‐formyl derivatives 3 from 1 and the corresponding 3‐carbaldehydes 4 from 2. 1,2‐Dihydro‐2‐imino‐7‐methyl‐1,6(6H)‐naphthyridin‐5‐ones 6a‐j are prepared by the Knoevenagel reaction of 4 with CH‐acidic nitriles 5. These reactions are carried out using a comparative study of conventional conditions (room temperature or reflux) versus microwave irradiation.