New Methodologies For The Synthesis Of 6-bromofuro[2,3-d]pyrimidine Bicyclic Nucleosides, Naphtho[1’,2’:4,5]imidazo[1,2-a]pyridines And Imidazo[5,1,2-cd]indolizines

Owing to their importance, the development of new methods to construct various heterocyclic scaffolds is an important task in organic synthetic chemistry. On the other hand, transition metal catalyzed reactions are emerging as an effective tool in organic synthesis and have found extensive applications in the preparation of heterocyclic compounds due to their simple operation process, mild reaction conditions, and high efficiency. Based on this background, this thesis designed and developed some new synthetic approaches toward fused heterocyclic compounds including 6-bromofuro[2,3-d] pyrimidine bicyclic nucleosides, naphtho[1’,2’:4,5]imidazo[1,2-a]pyridine and imidazo[5,1,2-cd]indolizine via transition metal catalytic cyclization reactions. The content of this thesis is listed as follows:Firstly, a novel synthetic approach toward 6-bromofuro[2,3-d]pyrimidine bicyclic nucleosides via condensation of the easily obtainable 5-formylpyrimidine nucleosides with carbon tetrabromide followed by intramolecular cyclization promoted by copper iodide has been developed. By using this method, structurally diverse 6-bromofuro[2,3-d]pyrimidine bicyclic nucleosides were synthesized. Compared with literature methods, this new protocol showed advantages such as broad substrate scope, simple synthetic procedure, mild reaction conditions, and high efficiency.Secondly, a novel synthetic approach toward naphtho[1’,2’:4,5]imidazo[1,2-a]pyridine and imidazo [5,1,2-cd]indolizine through dehydrogenative coupling of 2-phenylimidazo[1,2-a]pyridine with inner alkyne featured with cleavage of the C-H bonds located on different moiety of 2-phenylimidazo[1,2-a] pyridine has been developed. It is also found that this Pd-catalyzed dehydrogenative coupling is not efficient, but also shows good regio-selectivity when asymmetrical alkyne is used as a substrate.