The absolute configuration of the diol was determined by comparison of optical rotations with literature values. bThe absolute configuration of the diol was determined by comparison of optical rotations with that of an authentic sample (entries 3, 4). 8 Methanesulfonamide (1 equiv) is necessary for satisfactory turnover rates." Enantiomeric excesses were determined by GLC or'H NMR analysis of the derived bis-MTPA esters (see supplementary material ...