Direct Synthesis Of Amide From Benzonitriles And Benzyl Alcohols Via KOt-bu Mediated MPV-type Hydrogen Transfer Process

The transfer hydrogenation of carbonyl compounds with the use of transition metal is known as Meerwein–Ponndorf–Verley reaction(MPV reduction).This reaction has attracted extensive attention because of large amount of high-value products could be prepared by this method.The MPV reduction always preceeds under mild conditions,and it is very chemoselective for aldehydes and ketones,whereas other functional groups(e.g.,double bond,esters,acetals,etc.)remain unchanged,and this is the greatest advantage over the use of metal hydride reducing agents.The most popular catalysts are aluminum alkoxides in the traditional MPV reduction,and target products could be obtained after MPV reduction takes place under mild conditions.Several research groups have recently made some significant progress in transition-metal-free MPV type reductions,and imines can also react with alcohols through MPV-type reductions.Though MPV reduction has a wide range of applications,the poor atom economy is still a defect of th e reaction.Here,this article mainly demostrates the first time that MPV-type reduction can be accomplished between benzonitriles as oxidant and benzyl alcohols under transition metal free conditions,and the generated products can further react with each other.And amides as target product could be obtained after several MPV reductions.The main contents are as follows:(1)The methods of reduction by using metal hydrides,noble metals and cheap metals and the development of MPV reduction were briefly sum marized,and the background,significance and research plan of this thesis are introduced.(2)A series of experiments on the synthesis of amides through MPV-type reduction accomplished between benzonitriles and benzyl alcohols under transition metal free conditions has been carried out to explore the types and dosages of bases and solvents,temperature,gas environment and reaction time,and the range of substrates was expanded under the optimized conditions.(3)Based on the relevant literature and mechan ism experiments,a reasonable mechanism of the reaction was proposed.The reaction is initiated by Meerwein –Ponndorf–Verley redox process between benzonitrile and benzyl alcohol during which benzaldehyde(A)and phenyl imine(B)are produced respectively.The resultant phenyl imine(B)next undergoes another round of MPV redox process with another molecule of benzyl alcohol to give intermediate benzyl amine(C)and another molecule of benzaldehyde(A).These two will react together to generate hemiaminal intermediate D which subsequently reacts with another molecule of benzonitrile to give product E and phenyl imine(B)is regenerated and will react further to produce another molecule of E.From the scheme,we can see that the reaction is initiated with a MPV-process,but the subsequent reaction steps can actually form a reaction cycle that involves two rounds of MPV-processes.