The Study Of Asymmetric 1,3-Dipolar Cycloaddition Catalyzed By Chiral Oxazaborolidinone

Chirality is a universal phenomenon in nature,and it is also an important sign For the difference of life and non-life substance.Chiral compounds play a key role in medicinal,pesticide,materials,biological and life science.Asymmetric synthesis is an effective method of obtaining optical compound(chiral compound).Asymmetric catalysis,which employs catalytic amount of chiral source to realize the chiral catalytic cycle of the asymmetric catalysis,and synthesizes the chiral product with high optical yield,has shown great power and many chiral catalysts has been industrialized.Many excellent chiral catalysts are praised as chemzyme.In recent years,more attention has been attracted to the asymmetric catalytic synthesis,which is one of the most important synthetic methods in organic chemistry.Asymmetric hydroboration is a kind of widely applied and valuable reaction.This reaction can be used to prepare some key intermediates from some very simple starting materials,and can also be applied to create the first chiral center during the synthesis of some very complex natural product.Oxazaborolidine,which derive from the coordination of amino alcohol and borane,are good catalyst for the borane reduction reaction.A kind of fused cyclic oxazaborolidine invented by Corey and derived from proline has been successfully used in the production of MK-0417 as excellent chiral catalyst by Merck company.Although many amino alcohols have been developed,but excellent bis-amino are seldom found. It showed excellent properties in the borane reduction reaction.But the mechanism of the reaction applying the novel bis-amino is not clear.Thus,in this paper I studied the function and mechanism of this catalyst in the asymmetric borane reduction and discussed the mechanism for the single-centered catalyst proposed by Corey et al.Oxazaborolidine catalyst is a twisted chair structure.There is a partial bondbetween the O and B atoms.The interaction between N of the catalyst and results in the formation of the adduct,the formation reaction is exothermic.The formation of the adduct cause the B-H bond in the borane moiety to be weaked greatly.In this paper,chiral oxazaborolidine were synthesized.It was very efficient with perfect enantioselectivity when used in asymmetric 1,3-dipolar cycloaddition and asymmetric Aldol reactions.This paper mainly analysed asymmetric 1,3-dipolarr cycloaddition of cinnamene and N, a-two phenyl nitrones.The factors which may affect the results of the reaction and the mechanism of the asymmetric induction were discussed.