Chiral Diene Ligands In The Rhodium-catalyzed Asymmetric Reactions

On the basic of previously researching about bicyclo [3.3.0] framework,we designed and synthesized a new kind of tri-substituted chiral diene ligands with bicyclo [3.3.0] framework and used them as ligands in the Rhodium-Catalyzed asymmetric 1,4 addition and the asymmetric addition of arylboronic Acids to N-tosylarylimines. The reactions went on in excellent yield and high enantioselectivity. Basic on this more research about their application as ligands in asymmetric reactions have been done.First, we used the new chiral diene ligands in rhodium-catalyzed asymmetric addition of aryllboronic acids to isatins and got more than 95% yield, but the enantioselectivity of the reaction was poor (only around 50% ee). After optimization of the reaction solvents, temperature and ligands, we were able to obtain almost quantitative yield, but the ee value was yet not satisfying (only 62%ee). In this course we found the electronic effect of the ligands has obvious impact on the enantioselectivity of the reaction. So we tried to introduce electron-withdrawing groups to the substracts to improve the ee value of the reaction. But the results indicated that the electronic effect of the substrates could only affect the yield and had no obvious influence on the enantioselectivity of the reaction.Then,we used the diene ligands in the Rh-catalyzed addition reactions of arylboronic acids to aliphatic Imines and found that the reactions went on with excellent ee but low yield.This could be due to the existence of base and water in reaction system which could speed up decomposition or self-condensation of the alkylimine.So at the aim of avoiding the use of the base and runing this reaction in a neutral condition,we examed several Rhodium-diene complexes.To our delight, almost quantitative yield was obtained and the same excellent enantioselectivity with the complex [RhOHL]2 which need no base to speed up the transmetallation. A variety of aliphatic imines with different carbon chain in length and structure were all suitable substrate, providing the corresponding products in high yield (>90%) with excellent enantioselectivities (98%-99%).Furthermore we explored the feasibility of one-pot synthesis of chiral propidine and piperdine compounds in high yield with excellent enantioselectivities.