Cycloaddition Reactions Of Diazo Compounds And Nitrones

Diazo compounds（R₂C=N₂）are an important class of intermediates in synthesis,which can perform a series of chemical reactions under mild conditions.In addition,diazo compounds can form highly reactive metal carbene intermediates in the presence of transition metals,and undergo X–H（X=C,N,O,S,etc.）insertion reactions,cyclopropanation reactions,Ylide reactions and Wolff rearrangements,etc.Due to their unique structures,diazo compounds perform well in the construction of compounds containing cyclic skeletons,and are mostly used in medicinal chemistry,agricultural chemistry and the synthesis of natural products.As another class of"star molecules"in organic synthesis,nitrones have stable conformations and can be used as 1,3-dipoles in cycloaddition reactions to synthesize 1,2-azetidine compounds,and as electrophilic reagents in asymmetric nucleophilic addition reactions to produce hydroxylamine compounds.These compounds have important applications and are the dominant backbones in a wide range of natural products and drug molecules.This thesis focuses on the reactions of diazo compounds with nitrones catalyzed by different Lewis acids to produce a variety of heterocyclic compounds.The specific work is as follows:1.The[3+2]-dipolar cycloaddition reaction of diazoacetoacetate enone with N-aryl nitrone catalyzed by Sc（OTf）₃produced isoxazolidines with three chiral centers diastereoselectively and in high yields.2.Diastereoselective generation ofβ-lactams catalyzed by Rh₂（esp）₂.The reaction proceeds via a cascade reaction.In the presence of Rh₂（esp）₂catalyst,the first molecule of diazoacetoacetate enone reduces N-methyl nitrone to the corresponding N-methyl imine;the second molecule of diazoacetoacetate enone is rearranged by Wolff to generate vinylenone,which further reacts with the in situ generated N-methyl imine to diastereoselectively generateβ-lactams with two stereocenters.