Application Of N-Haloimide/Carboxylic Acid (DBU)Combination In Organic Synthesis

N-Bromosuccinimide (NBS) is a versatile reagent for synthetic organic chemistry.Traditionally, NBS can be considered as a convenient source of either cationic bromine usedin electrophilic addition reactions or bromine radical used in radical substitution reactions. Ingeneral, relatively inert succinimide would be generated as a by-product in the reaction. Fromthe atom economic point of view, direct installation of the succinimido moiety of NBS intothe target molecules, as well as further transformation thereby, is highly desirable. The dualrole of NBS providing both electrophilic bromine and nucleophilic nitrogen sources is thepersuit of chemists.In this thesis, we have developed novel and efficient cascade reactions for the synthesisof polysubstituted dihydrofuropyridinones,5-amino-3(2H)-furanones, ?-ketoamides,?-aminoketones, ?-aminoketones and allylic amine derivatives. Mechanisms of these newreactions are also investigated in details. These methods have apparent advantages, such asmild reaction conditions, readily available starting materials and high atom economy and soon.The thesis is divided into eight chapters. In chapter one, The application ofN-bromosuccinimide in organic reactions is reviewed. The thesis proposal is presented inchapter two.Chapter three, under mild conditions, bromonium ion initiated electrophilic cascadereaction of1-alkenoylcyclopropane carboxamides with NBS/HCCOH comdination wasdeveloped, which led to the production of dihydrofuropyridinones and5-amino-3(2H)-furanones. Such an efficient one-pot cascade transformation involves sequential C–Brformation and cleavage, C–N formation, C–C cleavage and formation, and C–O formation.The1,2-aryl migration involved in the reaction, to the best of our knowledgement, representsthe first example in ?,?-unsaturated enone system via halogen activation.Chapter four we have developed a practical and efficient protocol for the production ofhighly functionalized5-amino-3(2H)-furanones by the bromonium ion initiated electrophiliccascade reactions of1-acetylcyclopropane-carboxamides with NXS/RCOOH combination.Through in situ generated haloniumion intermediates, the reactivity of the ?-carbon to thecarbonyl group was converted from originally nucleophilic into electrophilic (umpolungstrategy), leading to the formation of a C O bond with an amide oxygen atom viaintramolecular electrophilic cyclization.Chapter five we have developed a simple and efficient new method for the synthesis of biologically important ?-ketoamides. This protocol avoided the use of expensive catalyst andharsh conditions generally adopted in the conventional method. In the whole process, DMFfunctions as nitrogen sources and solvent, which simplifies reaction and fully embodies atomeconomy.In chapter six?eight, as a general and practical animation reagent, a combination ofN-bromoimide and DBU has been developed. Under mild conditions, aryl alkyl ketones,chalcones and alkenes lead to ?-imidoketones, ?-imidoketones and allyl amines, respectively,with an NBS(P)/DBU combination. The mechanism of dual activation of DBU that DBU andN-bromoimide formN?Br?N asymmetric halogen bonding adducts via halogen bonding andlead to more electrophilic bromine and more nucleophilic nitrogen atoms simultaneously, wasproposed. In the reaction system, NBS(P) can play dual roles by act as both bromine andnitrogen sources. Relatively inert succinimide/phthalimide can being installed directly in thetarget molecule.