Study On The Synthesis Of Oximes Catalysed By Nitroxide Catalyst

As an important class of nitrogenous compounds,oximes can be used as intermediates,and have been found wide application in the synthesis of medicine,fine chemicals,and biologically active compounds,and the oxime group is a prevalent functional group in organic synthesis and can be easily used for functional group transformations,which can be either reduced to amines or oxidized to nitrile oxides,and they can also be dehydrated to nitriles or undergo an acid catalyzed Beckmann rearrangement to obtain amides.And oximes are also very important ligands in the formation of mono-and polynuclear metal complexes.In addition,oximes are highly crystalline compounds that have applications not only for protection,but also for purification and characterization of carbonyl compounds.Great effort has been made in the development of efficient procedures to construct these important compounds.The classic method to prepare oximes is mainly based on the reaction of a carbonyl compound with hydroxylamine hydrochloride in the presence of a stoichiometric amount of base.Despite this methodology is also applied industrially on a large scale for the production of various oximes,some drawbacks have restricted its further application:1)stoichiometric or excess amounts of hydroxylamine salt cost relative to the respective substrates and equal equivalent of base should be used relative to the hydroxylamine salt;2)large amounts of by-products are generated during the oximation reactions;3)the poor yields of the oximes because the resulting oximes can undergo either dehydration to nitriles or acid-catalyzed Beckmann rearrangement to amides.Nitrogen oxides,which is an important class of catalysts,has drawn considerable attention,due to their the unique behavior and eminent reactivity.In terms of sustainability,O₂ is the ideal terminal oxidation,H₂O is the by-product of catalytic oxidation reaction and this process has high selectivity,which decreases largely the amount of oxidant and the amount by-product.It is generally called "Green Chemistry Reaction".In this dissertation,using four types of nitrogen oxides for the synthesis of oximes were studied.The specific research contents include the following aspects.A simple and efficient catalytic system including TEMPO/acetaldoxime/InCl₃ for aerobic oxidation of primary amines to corresponding oximes by using toluene as the solvent is described.This practical method can use O₂ as the economic and green oxidant,tolerates a wide range of substrates,which can afford the target oximes in 71%-95%yields.A novel and efficient method for the aerobic oxidative synthesis of oximes direct from the corresponding alcohols using acetaldoxime as the nitrogen source under the catalytic system CuCl₂/DMAP/TEMPO is successfully achieved.This process is divided into two steps:one is the aerobic oxidation of alcohols to form the aldehyde intermediate;the other is the conversion of aldehyde into oximes.This whole process proceeds under mild condition,with high efficiency for a wide range of substrates,affording the corresponding oximes in 64%-94%yields.A general,efficient and metal-free method for aerobic oxidation of aromatic primary amines to corresponding oximes catalyzed by THICA/acetaldoxime with H₂O as solvent.This practical method can use air as the economic and green oxidant,water as the green solvent,tolerates a wide range of substrates,which can afford the target oximes in 75%-90%yields.A simple and efficient catalytic system for aerobic oxidation of primary amines into corresponding oximes was described,with 3-methyl-4-oxa-5-azahomo-adamantane as catalyst,acetaldoxime as co-catalyst and water as solvent.This process,which uses O₂ as economic and green oxidant,water as green solvent,tolerated a wide range of substrates,affording the target oximes in moderate to excellent yields.It was found that high selectivity was achieved when 3-methyl-4-oxa-5-azahomoadamantane was used,and E-type oximes were the only detected products in 71%-95%yields.A simple and efficient catalytic system for direct conversion of methyl arenes into aromatic oximes has been developed,with Cu?OAc?₂ as co-catalyst,NHPI as catalyst,TBN as both the nitrogen source and the oxidant.This process proceeds under mild conditions,tolerates a wide range of substrates,affording the targeted aromatic oximes in 63%-86%yields.