Transition Metal-catalyzed Coupling Of Aryl C-H Bonds With Carbonyl Compounds

Transition-metal-catalyzed C-H bond functionalization is an efficient approach to construct C-C bonds or C-X?carbon-heteroatom?bonds.Aryl esters are the core skeleton of many natural products and bioactive molecules,these compounds could be widely used to assemble complex molecules in synthetic chemistry.The traditional synthetic methodologies for aryl esters are focused on the coupling reaction of arenols or arylsilanes with carbonyl compounds.Therefore,the development of cheap metal-catalyzed aryl ester compounds has important scientific and practical value..In this paper,based on a review of the transition metal catalyzed aryl C-H bond functionalization,a series of naphthalene rings containing pyridine and amido functional groups were designed and prepared.We explored the first row transition-metal-catalyzed cross-dehydrogenative coupling of aryl C-H bonds with carboxylic acids using pyridine and amide as chelating-groups.This transformation provides an efficient synthetic approach to naphthalene ester compounds.The optimization of reaction conditions showed that Co?OAc?₂/Ag₂CO₃ catalytical system could enable the dehydrogenation coupling reaction of1-acylamido-substituted naphthalene with carboxylic acid.This transformation could tolerate a broad range of function group.All kinds of aryl carboxylic acids including heteroaromatic acids and aliphatic carboxylic acid can be efficiently converted to aryl ester compounds with the yield up to 92%.Aryl carboxylic acid with electron-deficient groups could be efficiently converted into aryl esters while the reaction conversion of electron-rich aryl carboxylic acids was lower.On the other hand,the electronegativity of substituents has low impact on cross-coupling of N-substituted naphthyl Csp²-H bond with carboxylic acids.1-amido naphthalenes with electron-donating and electron-withdrawing groups can afford1-acyloxy-8-amidonaphalene derivatives in moderate to good yields;It should be noted that N-?2-pyridylcarbonyl?-substituted methylene benzene compound could also introduced an acyloxy functional group in the ortho-position of benzylamine.All the structures of desired products were characterized by ¹HNMR,¹³CNMR,HR-MS and IR spectrum.The corresponding control experiment showed that the dehydrogenation coupling reaction of aryl C-H bonds with carboxylic acid involves cobalt?III?-catalyzed C-H bond activation process.The H/D exchange experiment indicated that the transformation perhaps proceeded through an irreversible cyclometalation pathway.Kinetic isotope effect further demonstrated that Csp²-H bond-breaking was possibly involved in the rate-limiting step of this reaction.The afforded products could be further used to assemble polyfunctional 1-acyloxy-7,8-diamino-substituted naphthalene.