An efficient method for the preparation of C2-symmetric, chiral alk-2-ene-1,4-diols (4) has been achieved, based on the borane-mediated reduction of symmetric alk-2-ene-1,4-diones (2) in the presence of oxazaborolidine (R)-1. In general, the presence of the double bond in 2 has been beneficial (compared with the related saturated 1,4-diketones 3) not only as far as the stereoselectivity in the reduction
desirable, especially since 1 : 6-addition is comparatively uncommon3. We have done this by reducing several substituted dibenzoylethylenes with aluminium isopropoxide in isopropyl alcohol, a reagent known to attack carbonyl groups while leaving olefinic linkages intact. The reductionproducts were invariably the corresponding diphenacyls, identified (after chromatographic adsorption) by mixed melting points