Mechanistic Insights into Asymmetric C–H Insertion Cooperatively Catalyzed by a Dirhodium(II) Complex and Chiral Phosphoric Acid

The reaction mechanism of methyl 2-diazo-2-phenylacetate (<b>DIA</b>) with 1-phenylpyrrolidine (<b>An</b>) cooperatively catalyzed by a dirhodium­(II) complex and chiral spirophosphoric acid (<b>SPA</b>) has been studied with the aid of DFT methods. The results show that the nucleophilic attack of <b>An</b> at the in situ generated carbenoid is preferred to give a metal-associated enol intermediate. In addition, a stronger interaction between the dirhodium­(II) complex and molecules such as the enol and chiral spirophosphoric acid is better for the asymmetric C–H insertion. This is due to the fact that a stronger interaction can restrict the chiral spirophosphoric acid around the dirhodium­(II) complex. In this case, the dissociated enol can be captured by chiral spirophosphoric acid immediately to give the major <i>S</i>-enantiomer product. Otherwise, the dimerization of enol molecules will occur followed by a self-catalyzed process to give the racemic C–H insertion product. This finding should be important for the design of other related dual catalyses in the future