Asymmetric synthesis of both D- and L-isomers of 5-thioglucose and 1,6-anhydro-5-thioaltrose are described. The key intermediates, L- and D-threose diethylacetal derivatives, were derived by chemical transformation from D-Xylose or D-arabinose and by Sharpless asymmetric dihydroxylation from gamma-hydroxycrotylaldehyde diethylacetal. They transformed to gamma-thiiranyl diethylacetal via trans-2,3-epoxy alcohol in seven steps. Acetic acid-promoted cyclization of gamma-thiiranyl diethylacetal gave 5-thiopyranoside. Removal of the protected groups under the acidic conditions afforded 5-thio-D- and L-glucose and 1,6-anhydro-5-thio-L- and D-altrose, respectively. (C) 2003 Elsevier Ltd. All rights reserved.