Microwave Irradiation for Catalyst and Solvent Free Knoevenagel/Michael Addition/Cyclization/Aromatization Cascades

A microwave-assisted reaction is developed to facilitate the construction of 1,2-dihydro[1,6]naphthyridines from methyl ketones, amines and malononitrile. This one-pot, catalyst-free, solvent-free, pseudo-five-component synthesis of [1,6]naphthyridines involves a sequential Knoevenagel reaction, Michael addition, ring closure and cyclizationaromatization cascades. The advantages of this method lie in its simplicity, cost effectiveness and environmental friendliness. High bond-forming efficiency, good yields and the use of readily available amines make this process convenient for parallel synthesis. Moreover, the versatility of nitrile as functional group is proved since it can be readily transformed into various other functional groups. It is believed that the time saved by implementing microwave strategy is potentially important in traditional organic syntheses and the combination of catalyst-free, solvent-free and microwave heating will be of importance in the search for green laboratory-scale synthesis.