Solvent-free synthesis of heterocyclic compounds using microwaves

Microwave-enhanced solvent-free synthetic approach is described that features simplicity, manipulative ease of the operation and conservation of solvents as the main advantages. This eco-friendly approach, which has found application in facile organic functional group transformations, is applied to rapid assembly of heterocyclic compounds. A variety of solid state reactions are described that occur rapidly at ambient pressure under solventless conditions and provide ready access to intermediates such, as enamines and alpha-tosyloxyketones which can be transformed in situ to biologically significant heterocyclic compounds such as isoflav-3-enes, flavones, quinolones, 2-aroylbenzo[b]furans and thiazoles in one-pot operation. Multicomponent reactions under these solvent free conditions can be adapted for high speed parallel synthesis and are exemplified by assembly of dihydropyrimidine-2(1H)-ones (Biginelli reaction) and imidazo[1,2-a]annulated pyridines, pyrazines and pyrimidines (Ugi reaction) which may have potential in building a library of such compounds.