Scheme 4.

Evaluation of C₂-symmetric catalysts with benzaldehyde (1a) as a model aldehyde. Reaction conditions: 1a (0.1 mmol), silane (0.15 mmol), catalyst (0.01 mmol), CH₂Cl₂ (0.4 mL); yields were determined by ¹H NMR spectroscopy with 1,1,2,2-tetrachloroethane as an internal standard following workup and enantiomeric ratios were determined by HPLC on a chiral stationary phase.