Study On The Catalytic Effect Of Chiral Bis-Oxazoline Metal Complexes On The Reaction Of Nitrone And Electron-Rich Alkene

1,3-dipolar cycloaddition reaction is an important reaction in research of basic theory of Organic Chemistry and synthetic methods, with important apply in syntheses of natural products and heterocyclic compounds. In the early 90th, enlightened by the apply of metal catalyst in asymmetry Diels– Alder reaction, Kanemasa et. al. first used metal-salt such as ZnI2,TiCl2(Oi-Pr)2 as catalyst in reaction of nitrones andα,β-unsaturated ketones. This explored a new field in 1, 3-dipolar cycloaddition reaction using metal catalyst. Especially to mention is the use of metal complexes with chiral ligands can synthesize compounds with optic activity from achiral compounds straightly. This afforded a brand-new way of synthesizing optic-active compounds with high stereoselectivity.This paper throws light on synthesis and catalysis effect of the complexes of copper (II) or zinc (II) with 2,2-bis[2,2'-4(S)-benzyl-4,5-dihydrooxazole]propane on the 1, 3-dipolar cycloaddition reactions of diphynyl nitrone with electron-rich ethyl vinyl ether under various reaction conditions.The research results show that chiral bis(oxazoline) metal complexes accelerate the reaction rate greatly. Compared with no catalyst condition, the reaction time shorts from 48h to 10min and the reaction rate is more than 280 times higher in the presence of copper complexes catalyst at room temperature. And chiral metal catalysts also have effect on the stereoselectivity, thus the endo/exo selectivity of the reaction is reversed in the presence of catalysts. The products are mostly endo in the presence of catalysts while exo- products are dominant in the absence of catalysts. The effect of ligand metal is observed on the catalytic effect. The change of reaction time with copper catalyst is 3.1 times than with zinc catalyst. The effect on stereoselectivity with copper catalyst is obvious than with zinc catalyst. When the reaction temperature and 4 ? molecular sieves is discussed, it is found that the rate of endo/exo increases slightly while the yield descends a little in lower temperature. The yield is improved with 4 ? molecular sieves but the stereoselectivity of the reaction is changed very little.