Reaction of a range of functionalised zinc/copper reagents, including those derived from α-amino acids, with the glucal-derived mesylate 7b leads to a mixture of C-3 and C-1 adducts, in which the former predominates. The stereochemistry of the adducts has been firmly established, and in each case the nucleophile was shown to have attacked from the β-face. By contrast, reaction of the iodohomoalanine-derived zinc reagent 3a with tri-O-acetyl-D-glucal in the presence of boron trifluoride etherate under sonication gives the α-adduct 19 as the major isomer. Conversion of this compound into a protected α-mannosyl C-linked α-amino acid derivative 23 is described.