| N-heterocyclic carbenes(NHCs)play a key role in organic catalytic reactions as a kind of organocatalysts.NHC-catalyzed reactions have emerged as one of the most-powerful strategies for the construction of complex molecules.Recently,remarkable advances have been made in NHC-catalyzed reactions that involve diverse activation intermediates,such as Breslow intermediates,homoenolate intermediates,α,β-unsaturated acylazoliums,saturated acylazoliums,azolium enolates and azolium dienolates.The first part of this thesis reviewed the development of NHC-catalyzed reactions in recent years,including the benzoin condensation,the Stetter reaction,hydroacylation reactions,substitution reactions,homoenolate reactions,acylazolium reactions,radical reactions,cooperative catalysis and through non-covalent bonding interactions catalyzed reactions.The second part mainly introduces that we have developed the first enantioselective NHC-catalyzed nucleophilic substitution reaction.A range of enantioenriched chromanones that contained all-carbon quaternary srereocenters were prepared.We optimized the reaction by screening various NHCs、solvents、bases and temperature etc and found the optimal conditions.Having identified the optimized conditions,we examined the method by varying the substituents on the alkene and aromatic ring.The desired chromanones contain all-carbon quaternary srereocenters were obtained in good yields and high enantioselectivities.We also examined the practicality of this catalytic process,a gram scale reaction was performed,the product was obtained in high yield and enantioselectivity.These products bearing all-carbon quaternary srereocenters could be antiformed into synthetically important intermediates.The electronic and steric properties of the substituents on the alkene played only anegligible role in the enantioinduction and the electronic properties of the aldehyde play an important role in the reaction efficiency.The third part mainly introduces that we have developed an efficient strategy for the synthesis of bisbenzopyrones by NHC-catalyzed intramolecular hydroacylation/Stetter reaction cascade.We optimized the reaction by screening various NHCs、bases、solvents and temperature etc and found the optimal conditions.Having identified the optimized conditions,we examined the method in a range of substrates with symmetrical and unsymmetrial substitution pattern of the aromatic ring,and the corresponding bisbenzopyrones were obtained in good yields.We also examined the practicality of this catalytic process,a gram scale reaction was performed,resulting in the desired product without losing any reaction efficiency. |
