Diastereo- and enantioselective synthesis of 1,2-diols by V(II)-promoted pinacol cross coupling

The V(II) promoted pinacol cross coupling of a chiral aromatic aldehyde with chiral aliphatic aldehydes occurs to afford syn diols in up to 91:9 diastereoisomeric ratio and up to 84% enantiomeric excess. The pinacol coupling of (S)-lactaldehyde and (R)-glyceraldehyde derivatives has also been studied and matching and mis-matching pairs have been identified. The stereochemistry of the products was established by correlation. The sense and degree of stereoselection is discussed.