Synergistic Reduction Of Organic Nitrile Compounds By Sodium Amidoborane And Lithium Borohydride

Nitrile compounds have been widely used in organic synthesis,pharmaceutical industry,material science and other fields.The reason is that the nitrile compounds have good chemical stability because of the C-N triple bond.Otherwise,most organic nitriles are readily available chemicals,both for industrial and lab experiments.For example,acrylonitrile is an important monomer for the production of plastics and acetonitrile is a common solvent for HPLC,LC-MS,and many organic reactions.Therefore,transformation of the nitriles which are inert but readily available into other useful reagents is an important reaction.However,due to the high bond energy of C-N triple bond,conversion of nitriles into other high-value chemicals such as amines often requires the assistant of transition metal catalysts.Borane compounds（for example:borane-tetrahydrofuran（THF-BH₃）,borane-dimethyl sulfide（DMS-BH₃）,ammonia borane（NH₃BH₃）,octahydrotriborate anion（B₃H₈-）,sodium amino-diboranate（NaNH₂[BH₃]₂））as good reductants,have been widely applied in the reduction of unsaturated bonds such as alkenyl,carbonyl,carboxyl,ester and nitro groups.However,the high temperature has to be used for the reduction of the C-N triple bond.In the thesis,we focus on the reducability of metal borane compounds.We developed a efficient method to reduce nitrile compounds to organic aminoboranes under mild conditions by using a "mixed" reductant consisting of NaNH₂BH₃ and LiBH₄.With the synergistic effect of NaNH₂BH₃ and LiBH₄,nitriles could be rapidly reduced to aminoborane in THF without catalysts,affording products with 99%yield.The products could be easily hydrolyzed to produce primary amines as well as utilized as reducing reagent for one-pot reductive amination.The advantages of this method are that it can be carried out without metal catalyst and harsh reaction conditions,and both of NaNH2BH₃ and LiBH₄ are inexpensive and easily available.The aliphatic nitriles and aromatic nitriles with electron-withdrawing groups（F,Cl,Br,I,CF3）,electron-donating groups（Me,OMe,Ph,N（CH₃）₂）,and heterocyclic nitriles such as thiophene,pyridine and indole（25 cases）showed good reaction performance.Furthermore,we found a synergistic effect between NaNH₂BH₃ and LiBH₄,the yield of reduction product decreaed from 92%to 22%or 12%when we used NaNH₂BH₃ or LiBH₄ alone.