ABSTRACT
Oxygen (O)-containing heterocycles are very abundant in nature due to their presence in various natural products like hormones, vitamins, and alkaloids. This chapter discusses the most important advances in palladium assisted syntheses of five-membered O-heterocycles. S. L. Buchwald and co-workers reported the synthesis of O-heterocycles via an intramolecular carbon-oxygen bond formation in the presence of palladium (Pd) catalyst. The incorporation of acetylenes in heterocycles by these new protocols was expected to find widespread applications in the synthesis of organic materials and bioactive compounds. The pyridine-possessing heterocycles, natural products, and synthetic intermediates were formed via an intramolecular Heck reaction. Good yields of a series of symmetrical and unsymmetrical nitrogen (N), O-, sulphur and silicon-containing tricyclic heterocycles were obtained under MWI. Heterocyclic chemistry has employed both intra- and intermolecular variations. Tetra- and pentacyclic N-fused heterocycles were afforded by the efficient Pd-catalyzed intramolecular carbopalladation/cyclization reaction.
