Electronic Control on Linear versus Branched Alkylation of 2-/3-Aroylbenzofurans with Acrylates: Combined DFT and Synthetic Studies

5 years ago

Electronic Control on Linear versus Branched Alkylation of 2-/3-Aroylbenzofurans with Acrylates: Combined DFT and Synthetic Studies

Kumar Vanka, Yadagiri Kommagalla, Chepuri V. Ramana, Kolluru Srinivas, Yuvraj Dangat

Investigations on the factors that govern unusual branched alkylation of 2-aroylbenzofurans with acrylates by Ru-catalyzed carbonyl-directed C−H activation has been carried out by calculating the kinetics associated with the two key steps—the coordination of the acrylate with the intermediate ruthenacycle and the subsequent migratory insertion reaction—studied with the help of DFT calculations. Eight possible orientations for each mode of alkylation have been considered for the calculations. From these calculations, it has been understood that there is a synergistic operation of the steric and electronic effects favoring the branched alkylation. Further DFT investigations on the alkylation of the isomeric 3-aroylbenzofurans indicated a preference for the linear alkylation and this has been verified experimentally. Overall, the observed/calculated complementary selectivity in the alkylation of 2-/3-aroylbenzofurans with acrylates reveals that the substrate-dependent charge distribution of the Ru−C bond in the intermediate ruthenacycle is an important determining factor and thus the current work opens up a new domain of substrate design for controlling regioselectivity. A play around the polarity of Ru−C: Substrate guiding of selectivity by changing the polarity of the Ru−C bond of the ruthenacycle in aroylbenzofurans (see scheme), in which 2/3-aroylbenzofurans result in different products under similar conditions, was proved by both density functional calculations (DFT) and experiment.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201700643