W. Guo, Tao Zhou, Yuanzhi Xia
Jun 11, 2015
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Organometallics
Abstract
The divergence between Rh(III)-catalyzed C–H activation/cycloaddition of phenyl- and 2-furanyl-containing benzamides with methylenecyclopropanes (MCP) was studied by DFT calculations. Calculations found that the C–H activation via a CMD mechanism is the most difficult step of the reaction involving phenyl. In contrast, the C–H activation of the 2-furanyl-containing substrate is kinetically easier but the formed five-membered rhodacycle is relatively unstable, making the following MCP insertion more difficult. Thus, different KIE data was obtained in experiments. The MCP insertion forms a seven-membered-ring rhodacycle intermediate, from which the chemoselectivity of the whole reaction is determined by the competitive pivalate migration (path I) and β-C elimination (path II). While the β-C elimination is lower in energy when a furanylene is contained in the intermediate, a reversed preference of pivalate migration was predicted for the phenylene counterpart. Structural analysis suggested that the unfavorab...