Carbon-hydrogen bonds are ubiquitous in organic compounds. If the C-H bonds could be used as a functional group, similar to a carbon-halogen bond, it would become one of the most powerful, valuable, straightforward methods for producing complex molecules and for the construction of C–C and of C–N bond frameworks. With this direction, transition metal catalyzed C–H activation has emerged as a powerful atom and step economic method to functionalize inert C–H bonds to install desired functional groups of great synthetic interest. Here, we are especially interested in cost-effective high valent cobalt(III) catalysed C-H functionalization over other precious metal like Pd, Rh, Ir etc. We revealed our results on amide directed hydroarylation of internal alkynes by cost-effective CoIII-catalysis to avail syn-selective mono- and dihydroarylated amide products selectively in an atom and step economic way. Four-fold C−H hydroarylation provided a highly conjugated organic framework in one step. We extended our methodology by employing intramolecular hydroarylation to achieve variously substituted benzofurans and 2-benzofuranones respectively. 5-exo dig attack is favoured over 6-exo dig attack in our condition and benzofuran products were accomplished directly in one pot. Benzofuranones were also synthesized under the same conditions but within much shorter reaction time. 5-substituted benzofurans were also synthesized through one-pot, two-fold, unsymmetrical C–H functionalizations by employing a second electrophile. Apart from the C-C bond formation, we have also developed a C–N bond-forming protocol using weakly co-ordinating ketone as a directing group and high valent Co(III) and Rh(III) as a catalyst. Competition experiments, kinetic studies with extensive deuterium labelling experiments indicated a base assisted intermolecular electrophilic substitution (BIES) reaction type mechanism, where C-H bond cleavage is the rate-limiting step.

Cp*CoIII-catalyzed C-C and C-N bond forming reactions through directed hydroarylation and amidation protocol: A route towards direct access of important heterocycles

2019 Spring National Meeting

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