Five-Membered Heterocycles

Abstract This chapter deals the chemistry, structural and reactivity aspects of saturated, and unsaturated five membered monocyclic and benzene fused heterocycles with mono nitrogen, oxygen and sulfur heteroatom such as pyrrole, pyrrolidine, indole, isoindole, indolizine, carbazole, furan, reduced furan, benzofuran, isobenzofuran, thiophene, reduced thiophenes benzothiophenes, and dibenzothiophene. Besides these, heterocycles with two similar or dissimilar heteroatoms, such as pyrazole, reducedpyrazoles, indazole, imidazole, imidazolidine, benzimidazole, dioxolane, dithioles and dithiolanes are delineated. The synthesis, reactivity and different applications of five-membered heterocycles with three or more similar or dissimilar heteroatms in five-membered and their benzofused analogs such as 1,2,3-, 1,2,4-triazoles, 1,2,3-benzotriazole and 1,2,3,4-tetrazoles, isoxazole, benzo[c]isoxazole, benzo[d]isoxazole, oxazole, benzoxazole isothiazole benzoisothiazole thiazole, benzothiazole, 1,2,3-, 1,2,4-, 1,2,5-, 1,3,4-oxadiazole/thiadiazoles are described.