New Methodologies For The Synthesis Of Fused N-heterocycles Based On The Diverse Reactivity Of Allenic Ketones

In this thesis, novel methods for the synthesis of some fused nitrogen-containing heterocycles via the one-pot multi-component cascade reactions of allenic ketones and other readily available reagents have been developed. It mainly includes the following two chapters:In the first chapter, a novel and efficient method for the synthesis of diversely substituted indolizines and its benzo derivatives via the one-pot multi-component cascade reactions of allenic ketones has been developed. Specific studies were as follows:Firstly, diversely substituted indolizines were efficiently synthesized through base promoted one-pot three component cascade reactions of allenyl ketones with α-bromo acetophenoes and pyridines.Secondly, functionalized pyrrolo[1,2-a]quinolines and pyrrolo[2,1-a]isoquinolines were synthesized with good efficiency through base promoted one-pot cascade reactions of allenyl ketones with α-bromoacetophenones and quinoline or isoquinoline.In the second chapter, a novel and convenient synthesis of pyrazolo[5,1-a]isoquinolines via palladium-catalyzed one-pot three-component cascade reactions of 1-(2-bromophenyl) buta-2,3-dien-1-ones has been developed. Specific studies were as follows:Under the mild conditions, 1-(2-bromophenyl)buta-2,3-dien-1-one was found to be able to undergo condensation with hydrazine hydrate to generate 5-(2-bromophenyl)-1H-pyrazole. Without isolation and purification, it was treated with ethynylbenzene. Under the catalysis of palladium catalyst, 5-(2-bromophenyl)-1H-pyrazole underwent Sonogashira coupling with ethynylbenzene followed by an intramolecular hydroamination to afford pyrazolo[5,1-a] isoquinoline with reasonably good efficiency.In summary, several novel, convenient and efficient methods for the synthesis of indolizines, pyrrolo[1,2-a]quinolines, pyrrolo[2,1-a]isoquinolines, and pyrazolo[1,5-a] isoquinolines have been developed in this thesis. Compared with literature methods, the protocols developed herein showed advantages such as high efficiency, simple synthetic procedures, cheap and easily obtainable starting materials, mild reaction conditions and broad scope of substrates. It is expected that these methods will find their applications in the preparation of related N-heterocycles.