Studies On C-H Functionalization Of Enamides And CBr₄ Promoted C-N Bond Formation Reactions

This paper mainly discussed the chemical reactions of enamides,including the recent advances in the study of enamides chemistry and the studies of three different types of chemical reactions based on enamides.The aim of this study is to enrich the application of enamides in organic synthesis chemistry.At the end of the paper,a method for the synthesis of poly-substituted imidazoles based on CBr₄ promoted C-N bond formation was introduced.This paper included these five chapters:Chapter 1: The advances in enamides chemistry.As a class of important organic synthesis precursors,enamide is widely used in the construction of organic skeletons containing nitrogen heteroatoms.This chapter mainly introduced recent advances about the applications of enamides in cyclization reactions,β-C-H functionalization reactions and Friedel-Crafts reactions.These new strategies make enamides as ideal "star molecule" to achieve a variety of functional transformation through a simple operation,enriched the application of enamides in organic synthesis.Chapter 2: CuBr₂-mediated aerobic oxidative synthesis of 3-bromo-imidazo[1,2-a]pyridines with pyridines and enamides.In this chapter,we introduced a method for the synthesis of 3-bromo-imidazo[1,2-a]pyridine by CuBr₂-promoted coupling of enamides and pyridines in a one-pot manner.This procedure employs oxygen as an oxidant,and uses Cu/O₂ catalytic system to achieve the formation of C-N bond and C-Br bond.The direct use of pyridine,to avoid the prefunctionalization of substrates and to reduce the operational steps,provides a new route for the synthesis of 3-bromo-imidazo[1,2-a]pyridine compounds.Chapter 3: Efficient transformation of enamides into α-acyloxy ketones via an acyl intramolecular migration process.In this chapter,we described a metal-free strategy for the β-acyloxy of enamides.Just mixing the enamides in a solution of anhydride and hydrogen peroxide in proportion can efficiently synthesize α-acyloxy ketones at room temperature through an acyl intramolecular migration process.Simple operation with inexpensive reagents provides a novel and efficient method for the synthesis of α-acyloxy ketone compounds.Chapter 4: The self-coupling of enamides catalyzed by NIS and K₂S₂O₈.In this chapter,we presented a transition-metal-free self-coupling reaction of enamides.This procedure uses NIS and K₂S₂O₈ to complete the self-coupling of enamides under mild conditions.After initiated by only a small amount of NIS and K₂S₂O₈,the reaction can be carried out smoothly under an auto-catalyzed way,and the self-coupling of enamides can be completed rapidly,which provides a new transition-metal-free catalytic pathway for the construction of nitrogen-containing quaternary carbon centers.Chapter 5: CBr₄ promoted cyclization of amidines with 1,3-dicarbonyl compounds or ketones.In this chapter,we demonstrated a metal-free CBr₄ promoted tandem cyclization of amidines with 1,3-dicarbonyl compounds or ketones to synthesize polysubstituted imidazoles under mild conditions.CBr₄ is employed to promote C-N bond formation through an in situ α-C-H bromination process of ketones and then successfully synthesize this skeleton.This strategy provides a very practical method for the synthesis of multi-substituted imidazoles.