Butane-2,3-Diacetal-Desymmetrized Glycolic Acid-A New Building Block for the Stereoselective Synthesis of Enantiopure alpha-Hydroxy Acids We thank the EU (Marie Curie Fellowship to E.D.), the EPSRC (to D.J.D.), the Novartis Research Fellowship (to S.V.L.), and Pfizer Gobal Research and Development, Groton, USA, for financial support.