Synthesis and stereochemical characterization of optically active 1,2-diarylethane-1,2-diols: Useful chiral controllers in the Ti-mediated enantioselective sulfoxidation

The series of phenylsubstituted 1,2-diphenylethane-1,2-diols 2a-h was prepa red in high chemical (70-80%) and optical yields (similar to 90%) by Sharpl ess syndihydroxylation of the corresponding (E)-1,2-diarylethenes, in turn obtained by McMurry or Wittig reactions. The enantiomeric excesses of the s amples were determined by HPLC analysis using Chiralcel OD chiral stationar y phase (CSP). This CSP was able to resolve all the diols, except for 2g, w ith alpha values ranging between 1.10-1.64. In all cases the (R,R) antipode was eluted first. (R,R) absolute configuration was assigned to the dextror otatory (CHCl3) diols 2a-h by analyzing the CD spectra of their 2,2-dimethy l-1,3-dioxolanes 3a-h. In fact, the CD spectra of all these dioxolanes pres ent a positive couplet (210-180 nm range) which can be nonempirically relat ed to an (RR) absolute configuration of the two stereocenters. (C) 2001 Wil ey-Liss, Inc.