Regioselective and Stereospecific Halosilylating Cleavage of the Oxirane System of Glycidol Derivatives as an Efficient Strategy to C2‐ O ‐Functionalized C3‐Vicinal Halohydrins

Glycidyl esters and ethers undergo a regioselective andstereospecific opening of the oxirane ring upon treatment with trimethylsilyl halides (TMSX, X = Cl, Br, or I) in the presence of pyridine to produce the corresponding C2‐ O ‐trimethylsilyl‐3(1)‐halo‐ sn ‐glycerols in high yields. Trifluoroacetylation across the trimethylsilyloxy system of such C3‐synthons with trifluoroacetic anhydride (TFAA) in the presence of a halide anion (e.g. Bu 4 NX; X = Cl, Br, or I), followed by removal of the trifluoroacetyl transient protection, provides nearly quantitative access to the respective vicinal haloalkanols. Alternatively, C2‐ O ‐acylated vicinal halohydrins can be obtained in a highly chemo‐/regiospecific manner by direct conversion of the trimethylsilyl protecting group into short‐ or long‐chain ester functionalities by means of a three‐component reagent: pyridine–carboxylic acid–TFAA. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)