Synthesis and ruthenium catalyzed enantioselective hydrogenation of 1,3-dihydroxypropan-2-one 1-ethers

A number of 3-O-substituted 1,3-dihydroxypropan-2-ones have been synthesized in view of their potential use as prochiral precursors of optically active glycerols. Indeed, the oxo-ethers have been reduced to the corresponding 3-O-substituted glycerols via chiral Ru complexes derived from (S)-binap, ( = (-)-(S)-2,2'-bis(diphenylphosphino)-1,1'-binaphthalene) with enantiomeric excesses up to 93%. The steric course or the catalytic reduction appears to be essentially dependent on the steric encumbrance or the substituents; indeed, a dramatic increase of the enantiomeric excess is observed when the bulky trityl group is substituted by the less encumbering benzyl or octadecyl groups.