. ^c^Determined after purification by flash chromatography. ^d^Determined by HPLC with chiral stationary phase. ^e^Calculated from *c* = ee~s~/(ee~s~ + ee~p~). ^f^ *E* = ln\[0 − *c*(0 + ee~p~)\]/ln\[0 − *c*(0 − ee~p~)\]. ^