N-heterocyclic Carbene-Catalyzed Asymmetric Synthesis Of γ-lactams And Tetrahydropyridin-2-ones

This thesis is composed of three parts:(1)y-Lactams(pyrrolidin-2-ones)and their derivatives containing the y-lactam core are important synthetic targets and often display interesting biological activities.This chapter highlights efficient strategies leading to these compounds and synthetic methodologies are classified according to the key step of the lactam ring formation starting from acyclic precursors.The synthetic methodologies including radical cyclization and bond formation mediated by transitional metals,phase transfer catalyst,Br(?)sted acids,amines and N-heterocyclic carbenes are summarized.(2)We have developed an efficient N-heterocyclic carbene-catalyzed stereoselective cascade reactions of α-bromoenals and 1-aryl-2-(4-methylbenzenesulfonamido)ethanones.A series of chiral disubstituted y-lactams with two stereogenic centers was afforded in high yield(up to 98%)with good diastereo-(up to 10:1 dr)and excellent enantioselectivities(up to>99%ee).In addition,the first formal[3+2]cycloadddition reaction involving a-bromo-enals catalyzed by NHC was achieved.This strategy extends the scope of NHC-catalysis.(3)N-Heterocyclic carbene-catalyzed stereoselective cascade reaction of a-bromoenals and trifluoromethyl substituted enamines based on α,β-unsaturated acylazolium intermediates has been developed.Functionalized tetrahydropyridin-2-ones containing trifluoromethyl group were obtained in good yield(up to 95%)with excellent enantioselectivity(up to 98%ee).