Study On The Catalytic Action Of TADDOL Metal Complexes On The Reaction Of C, N-Diphenylnitrone And Electron-Deficient Alkene

The 1,3-dipolar cycloaddition reaction is a common method for construction of five-membered hetereocyclic compounds. By using chiral metal complexes as catalysts, study on the synthesis of optically active products directly from achiral 1,3-dipolar reagents and achiral alkenes, is a focal point of research in asymmetric synthesis along with going deep into further research, after the first transition-metal catalyzed asymmetric 1,3-dipolar cycloaddition reaction reported in 1994. Electron-deficient alkenes which cotain the structure ofβ-diones, can coordinate to chiral metal complexes to obtain the favorable stereoselectivity, so these are widely used in asymmetric 1,3-dipolar cycloaddition reaction of nitrones.Based on the effect of coordination compound formed by catalyst and alkene, in this paper, we design and synthesize a new chiral 1,4-diol(TADDOL) ligand cotaining thiophene rings, which complexes with two different titanium reagent to form two new chiral TADDOLate-TiClX metal catalysts.We study the 1,3-dipolar cycloaddition reaction of C,N-diphenylnitrone and 1-N-((E)-2-butenoyl)succinimide catalyzed by TADDOLate-TiClX as chiral metal catalysts. Monitoring reactions by thin layer chromatography(TLC). The endo/exo ratios are determined by 1H-NMR. The prodcts are separated by silica gel column chromatography. The enantiomeric excess(ee) of products are determined by HPLC using a chiracel OD-H column. The influence of catalysts, catalyst amount on the diastereo- and enantioselectivity are investigated by analysis of a series of above experimental data.When using 25mol% TADDOLate-TiCl2 as catalyst, the reactants reacted for 144 hours in dichloromethane at 10℃, we obtain an endo/exo ratio of 10/90 with an ee of 97% exo isomer. However, when catalyst amount reduces to 10mol%, under the same conditions, we obtain an endo/exo ratio of 15/85 with an ee of only 55% exo isomer. Other things being equal, when using 10mol% TADDOLate-TiCl(OTos) as catalyst, we obtain an endo/exo ratio of 5/95 with an ee of 87% exo isomer.