Metal–Nitroalkene and <i>aci</i>-Nitro
Intermediates in Catalytic
Enantioselective Friedel–Crafts Reactions of Indoles with <i>trans</i>-β-Nitrostyrenes
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Abstract
The half-sandwich aqua complex (<i>S</i><sub>Rh</sub>,<i>R</i><sub>C</sub>)-[(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)Rh{(<i>R</i>)-Prophos}(H<sub>2</sub>O)][SbF<sub>6</sub>]<sub>2</sub> (Prophos = propane-1,2-diylbis(diphenylphosphane))
efficiently catalyzes the asymmetric reaction between <i>N</i>-methyl-2-methylindole and <i>trans</i>-β-nitrostyrenes
(up to 94% ee). The metal–nitroalkene complex involved has
been characterized by X-ray crystallography, and the <i>aci</i>-nitro intermediate complex has been spectroscopically detected.
A plausible catalytic cycle is proposed
