Research On The Coupling Reactions Of Oxime Derivatives

Green chemistry,which was also called sustainable chemistry,is an area of chemistry and chemical engineering focused on the designing of reaction modes and technological approaches to preventing pollution and reducing consumption of nonrenewable resources.The concept has been increasingly accepted by everyone in the context of increasing attention to problems of chemical pollution and resource depletion.Oximes derived from carbonyl compounds have been widely used in diverse laboratory and industrial applications.Beckmann rearrangement which are widely used in the industry for the preparation of nylon 6and nylon 12,is the best know conversion reactions about oximes.Over the past few decades,more and more coupling reactions involving oximes reactions have been developed through transition-metal catalyzed process.The oxime derivatives have weak N–O bonds with an average energy of 57 kcal.mol^-1,which is much less than the energies of the C–X?X=C,N,O??69–91 kcal mol-1?bonds.The N–O bond cleavages of oxime derivatives was generally favored,thus frequently being utilized to initiate further transformation for constructing a range of nitrogen-containing compounds.In many cases,oximes derivatives can be used as both reactants and oxidants and the reaction systems do not need external oxidants.These transformations alway feature extremely mild conditions,broad substrate scope and good chemical selectivity.In this context,the works on transition-metal catalyzed coupling reaction involving oximes have been systematically studied without the require of external oxidants,and a variety of nitrogen-containing organic molecules have been efficiently constructed.The details are summarized as follows:In chapter two,we developed an efficient strategy for synthesis of isoquinolines via Pd?II?-catalyzed cyclization reaction of oximes with vinyl azides as[3+3]and oximes with oximes as[4+2]cycloaddition.Oximes could serve as a directing group and an internal oxidant in the transformation.This reaction features good functional group tolerance and mild conditions.In chapter three,a novel and versatile method for the synthesis of 2H-imidazoles via iron-catalyzed[3+2]annulation from oxime acetates with vinyl azides has been developed.In the existing reports,the synthesis of 2H imidazole derivatives is very few and cumbersome.This transformation used inexpensive iron salt as a catalyst,used easily available material as reaction substrate.This denitrogenative process involved N-O/N-N bond cleavages and two C-N bond formations to furnish 2,4-substituted 2H-imidazoles.It was performed under mild reaction conditions and needed no additives or ligands.Furthermore,this is a green reaction involving oxime acetate as internal oxidant,acetic acid and nitrogen as byproducts.In chapter four,we researched an efficient and external-oxidant-free iron-catalyzed[2+3]annulation of oxime acetates with 1,4-dithiane-2,5-diol has been developed for the construction of functionalized 3-thiazolines.This efficient protocol can achieve the equivalent conversion of oxime ester to 3-thiazolines.It is a environmentally friendly transformation which used ethanol as a solvent and reacted in mild reaction conditions.In chapter five,we developed a practical copper-catalyzed[3+2]annulation for the synthesis of thiazol-2-yl ethers from oxime acetates with xanthates.Excellent functional group tolerance of oxime acetates derived from aryl ketones,alkyl ketones makes this reaction practical.Furthermore,this transformation provided a efficient strategy for the structure modification of natural product.Experiments showed that the regioisomeric preferences may be relating to the preference for the site of enolization and the one with fewest hydrogen substituents was the major product.Unique dihydrothiazole product also could be obtained from the specific substrate.In chapter six,an efficient copper-catalyzed C?sp³?-H oxidative functionalization of aromatic oxime acetates with?-oxocarboxylic acids was researched.This process involved the formation of radical and the selective radical/radical cross-coupling between benzoyl radical and?-carbon radical.This transformation also features good functional group tolerance and no need for ligands or additional bases.It is worth noting that the enamine groups were preserved due to the stabilizing effect of intramolecular hydrogen bonds.In chapter seven,an efficient and straightforward zinc-promoted rearrangement of oxime acetates with arylamines for the synthesis of amidines has been developed under mild conditions.This process involves N-O/C-C bond cleavages and C-C/C-N bond formations.Various oxime acetates and arylamines are suitable for this transformation.Furthermore,diverse arylbenzimidazoles could also be prepared through simple one-pot procedure.