ABSTRACT
Heterocyclic compounds have a wide range of applications. They are predominant among the type of compounds used as pharmaceuticals, agrochemicals, veterinary products, etc. The recent introduction of single-mode technology assures safe and reproducible experimental procedures and microwave synthesis has gained acceptance and popularity among the synthetic chemists (Hayes, 2002). Microwaves are highly important in green synthesis of heterocyclics. Heterocyclic ring formation can be classified in many types depending on the size of ring and number nature of hetero atoms (N, O, S., etc.). The major classes are –
Five Membered Heterocyclic rings • Pyrroles • Pyrazoles • Imidazoles • Oxadiazoles • Triazoles and tetrazoles • Isoxazolines and pyrazolines
Benzoderivatives of Five Membered ring • Benzimidazoles, Benzoxazoles and Benzthiazoles • Indoles • γ-Carbolines
Six Membered rings • Dihydropyridines • Dihydropyridopyrimidinones • Dihydropyrimidines • Tetrazines
Polycyclic Six Membered rings • Quinolines and substituted Pyrimidines
Medium Sized Heterocycles
The classical Paal-Knorr cyclization of 1.4-diketones to give pyrroles was dramatically speeded up under microwave irradiation with high yields (70-90%).
