Directing Groups Assisted Rh-catalyzed Inert C-H Bond Activation And Functionalization

Transition metal catalyzed inert C-H activation and functionalization is one of the hot topics in current organic synthesis,and has been used as an efficient strategy to construct C-C and C-X bonds.In these reported systems,regioselectivity control can be easily achieved by introducting the directing groups into substrates.A variety of transition metal catalysts have been employed in C-H bond activation reaction,but majority of them are not so efficient in some reported systems.In contrast,the stable rhodium complexes are highly active enough to catalyze organic transformations,in which good functional group compatibility and selectivity are observed.Meanwhile,Rh-catalyzed system also shows more advantages over the common coupling reactions,including simple operation and high efficiency and so on.So far,much advancement has been achieved by Rh-catalysis,but the narow scope of reaction type extremely limited the development of inert C-H bond activation and functionalization.The establishment of efficient Rh-catalyzed C-H activation is highly desirable in organic synthesis.Based on the understandings,this thesis mainly focuses on employing Rh catalysts to enable the relating ortho C-H functionalization of aryl azobenzenes and diarylnitrone,respectively.The results are listed as follows:(1)The direct alkylation of aryl azobenzene with allyl acetates was successfully realized in the presence of bis[(pentamethylcyclopentadienyl)dichloro-rhodium]([Cp*RhCl2]2),silver hexafluoroantimonate(AgSbF6),1,2-dichloroethane(DCE),which proceded at 110 oC for 20 h to generate the products in moderate to good yields.The results shows that selective alkylation was obtained by employing allyl acetates as unique alkylation agents,but no alkenylated product was isolated in the reaction system.The silver hexafluoroantimonate as the additive,as the reaction solvent,in a mild conditions to achieve compounds with through C-H activation and functionalization is demonstrated in which the can be carried out at the ortho position of azobenzenes,The ortho-alkylation reaction of azobenzenes was first developed under Rh catalysis,which provides a highly efficient and atom-economic approach to a series of asymmetric azobenzene compounds.(2)A direct cross-dehydrogenative coupling strategy was adopted for the Rhcatalyzed coupling reaction of aryl azobenzenes with N-methylindole,benzoxazole andbenzothiophene,affording the corresponding product in good isolated yields.During the study,it was found that the presence of AgSbF6 and Cu(OAc)2?H2O was requisite for the excellent regioselectivity observed in the CDC reaction.This method provides a brand-new synthetic method for the synthesis of highly conjugated aromatic compounds.(3)The Rh(?)-catalyzed direct amination reaction of N-a-diphenylnitrone with dioxazolones derivatives has been well-established.The optimization of reaction conditions shows that DCE was the best reaction medium.In addition,AgSbF6,NaOAc and glacial acetic serving as additives were necessary for the direct functionalization of aromatic C(sp2)-bond within the N-a-diphenylnitrone substrates.Furthermore,it was found that the corresponding products underwent direct hydrolysis to release aromatic aldehydes after the amination reaction.Therefore,this amination provides a new alternative method for the synthesis of o-aminobenzaldehyde and its derivatives.