Palladium Catalyzed Enatioselective Hydroesterification Of Olefins

Carboxylic acids and esters are important compounds with many kinds of biological activities.Palladium catalyzed hydrocarboxylation and hydroersterifi-cation of olefins provides an effective way to synthesis them.The asymmetric processes are of great significance for which can introduce an asymmetric center into products.Besides,developing new CO surrogates which can avoid using toxic CO gas in hydrocarboxylation and hydroersterification reactions is another important direction.Our study about the enatioselective hydroesterification of aryl olefins will focus on three aspects as the follows:(1)Our group has reported a palladium catalyzed regioselective hydroesterifi-cation of alkenyl phenols with phenyl formats as CO source.Based on the pre-work,we find that optical active 3,4-dihydrocoumarins can be obtained in 92%yield and up to 91%ee by using(R)-(-)-DTBM-SEGPHOS as ligand.This reaction can be easily operated with phenyl formate under relative low temperature.The isotopic experiments show that the acyl group of products comes from the phenyl formate rather than the formic acid.Based on the mechanism experiments,a catalytic cycle is proposed.This study lays the foundation of the asymmetric intermolecular hydroesterification of aryl olefins.(2)Based on the studies above,it is find that 2-arylpropanoates can be obtained in up to 92%yield with>20/1 b/1 ratio and up to 95%ee.The reaction can be readily extended to a wide variety of meta-and para-substituted aryl olefins and can be carried out on a gram scale which implies the possibility of being used widely.The optical active esters can be transformed to corresponding carboxylic acid and amide without loss of ee.It is also find that branch esters can be obtained with same ee and relatively higher regioselectivity by using CO gas.This finding provides the direction of the further researches.(3)Based on the studies above,the enantioselective hydroesterification of 2-phenyl propylene is investigated.Various chiral ligands are screened and only 10%ee is achieved.Reactivity can be improved by adding strong acid while the enaitoselectivity still be low.Besides,conditions about hydroesterification of olefins with CO gas are screened.Experiments show that CO pressure and the amount of phenol can affect the yield,regio-and enantio-selectivity.Higher or lower loading of CO gas and phenol will cause the decrease of yield and ee.The range of substrates will then be extended.