aThe reactions were performed with aldehyde (0.01 mmol), ketone (0.5 mmol), and catalyst 4b (0.01 mmol) at rt. bCombined yield of isolated diastereomers. cDetermined by 1H NMR of the crude product. dDetermined by chiral-phase HPLC analysis for anti-products. Adapted from reference . Copyright 2012 American Chemical Society.