Silver-Catalyzed Reduction Of Quinoline Compounds In Water

Heterocyclic compounds,especially N-heterocycles,are the most important compounds in the pharmaceutical and agrochemical industries,with drugs containing N-heterocycle backbone accounting for about 60% of all drugs.The structure of 1,2,3,4-tetrahydroquinoline is a very common organic framework and widely found in many natural products,biologically active,and known drug molecules.Given the importance of these frameworks in drug screening and medicinal chemistry,the development of new methods for the synthesis of 1,2,3,4-tetrahydroquinoline compounds remains an active and very important area of research.Among the many synthetic methods known,direct catalytic hydrogenation of quinoline compounds is one of the simplest,quickest and most efficient methods.At present,the catalysts for hydrogenation of quinoline compounds are mainly noble metals Pd,Pt,Ir,Rh,Ru,inexpensive metals such as Ni,Co,Fe and metal-free Lewis acid-base.As one of the commonly used catalysts,silver has been widely used in organic conversion processes,and its potential application in the fields of drugs,materials and basic raw materials chemicals has attracted more and more attention.However,there has rarely been a report on the hydrogenation reduction of unsaturated compounds under silver catalysis.In recent years,various metal hydrogen species have been characterized by chemists and applied to various reduction reactions.Although silver-hydrogen species have long been characterized,due to their high stability,only a handful of articles have reported on the organic synthesis of silverhydrogen.In this paper,we have developed a new method for the reduction of quinolines and other electron-deficient azahenes by silver catalysis.Hydrosilane is used as a safe reducing agent,and water is used as a green solvent to obtain a series of 1,2,3,4-tetrahydroquinoline and other useful N-heterocyclic compounds.The reaction is carried out under mild and easy-to-operate conditions,avoiding the use of hydrogen which is dangerous to explode,and the reduction product of the quinoline compounds can be obtained in good yield and selectivity without using any additional ligand and base.More importantly,the process can rapidly achieve the reduction of various functionalized quinolines in as little as 10 minutes.Preliminary mechanism studies indicate that the reaction is most likely to produce Ag-H species in situ,followed by a gradual 1,4-/1,2-addition reaction of quinoline compounds to give 1,2,3,4-tetrahydroquinoline compounds.