Transition Metal-Catalyzed Hydrogenation Of Esters And Enamides

Reductions of Ester and enamide are very important reactions in organic synthesis.The products of hydrogenation like alcohols and chiral amines are significant chemical intermediates,which have applications of daily chemical industry and pharmaceutical.Traditionally,ester reduction was carried out with stoichiometric metal-hydride reagents(e.g.NaBH4 and LiAIH4),which are not stable in the air,difficult to operate and multifarious reaction post-processings.In comparison,hydrogen is one of green reduction reagents and can be used as a substitution of expensive metal hydride reagents to avoid the above drawbacks.Although some simple esters have been reducted by heterogeneous catalytic hydrogenation in industry,the reaction conditions are very harsh,shall be carried out under the condition of high temperature and high pressure which is of large energy consumption and uneconomical.Recently,homogeneous catalytic hydrogenation of esters has made great progresses,all kinds of skeletons and coordination models of catalyst emerged endlessly,but there are still some problems such as low efficiency,harsh reaction condition.Thus,it is necessary for the realize of highly efficient ester reduction to develop new ester reduction catalyst.Asymmetric hydrogenation of enamide is one of the most effective methods to synthesis of chiral amine compounds.At present,various types of enamides have been successfully hydrogenated,with excellent yields and enantioselectivity.However,due to the steric hindrance effect of the substrate and other effects,tetra-substituted enamines are difficult to hydrogenation and rarely reported.According to the scientific problem,this paper mainly researched the hydrogenation of esters and tetra-substituted enamines,the concrete content includes:1)We designed and synthesized a kind of bipyridin-2-ylmethanamine contained tetradentate nitrogen-phosphine ligand,with Ru(PPh)3Cl2 coordination to get the stability of the complexes,the structure of the new catalyst was determined by single crystal diffraction and the catalyst was applied in ester reduction.Research shows that the catalyst has an efficient application in hydrogenation of ester in relatively mild conditions(80 ?,50 atm H2)and a wide range of substrates,TON(turnover numbers)up to 9700.2)In this paper,a series of tetra-substituted enamines with amide groups havebeen studied,which can be asymmetric hydrogenated by Rh-DuanPhos catalytic system successfully.A range of important chiral amines can be obtained with high yields and enantioselectivity(up to 99%yield,up to 95%ee).