Cascade Reactions Of Arylhydroxylamines By Nucleophilic Aromatic Substitution

The N-O ? bond of arylhydroxylamines has an average energy of ~57 kcal/mol which owning to the repulsion of the lone electron pairs on the nitrogen and oxygen atoms.Thus,the N-O ? bond is more reactive than the C=C bond and a C-X bond(X=C,N,O),which results in the cleavage of N-O ? bond and subsequent the arrangement of arylhydroxylamines.The biaryl motif is an important structure in nature products and drug molecules,and the preparation of biaryls compounds has always been a hot issue in organic synthesis.This thesis developed a cascade SNAr approach for the synthesis of structurally diverse biarys from the arrangement of arylhydroxylaminesThis paper consists of three parts.The first part contains the background of the synthesis of biaryl compounds and its basic reaction mode.In this chapter,we succinctly describe the transition-metal-catalyzed cross-coupling of arylhalides with organometallic reagents,for instance,Cu catalysis and Ni catalysis.We focus on the Pd-catalyzed dehydrogenative cross-coupling of two aromatics and C-H activation in the presence of directing group.In addition,several transition-metal free approaches to synthesize biaryls have been introducedIn the second part,we developed a cascade approach to synthesize NOBIN analogues from arylhydroxylamines and electron-deficient haloarenes in the absence of transition metal.Based on the control experiment,we proposed a possible mechanism in the presence of K3PO4.This cascade process includes the formation of a transient N,O-diarylhydroxylamines intermediate,via direct O-arylation in the presence of K3PO4,that then undergoes rapid[3,3]-sigmatropic rearrangement and rearomatization to construct biaryl products.This operationally simple synthetic strategie owns excellent stereoselectivity,high atom economy,and readily available substrates in the absence of additional catalyst.The reaction affords structurally complex NOBIN products that would otherwise be difficult to access by other methodsIn the third part,we utilized arylhydroxylamines as substrate to couple with aryl electrophile which is derived from the cleavage of C-S bond of arylsulfonium salts,and structurally diverse biaryls were obtained.In addition,aryldiazonium tetrafluoroborates were used to couple with arylhydroxylamines in the existence of Cu catalyst which is crucial to this transformation.Arylsulfonium salts and aryldiazonium tetrafluoroborates rely on a cascade of reaction with arylhydroxylamines that show important synthetic value to construct highly functionalized NOBIN-type products.