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 (DIA) with 1-phenylpyrrolidine (An) cooperatively
catalyzed by a dirhodium­(II) complex and chiral spirophosphoric acid
(SPA) has been studied with the aid of DFT methods. The
results show that the nucleophilic attack of An 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 S-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.