3-fluoro-6-tert-butyltetrahydropyranosyl trichloroacetamidates.: "Chiral auxiliary donors" for hydroxyalkyl radicals

[GRAPHICS] An improved THP-based chiral auxiliary for hydroxyalkyl radicals is reported. The key modifications involve introduction of a fluorine substituent at C-3 to make the acetal center more robust and the use of Schmidt's trichloroacetamidate glycosylation methodology for efficient attachment of the auxiliary to the radical precursor. The resulting chiral hydroxyalkyl radical equivalents add to methyl 2-trifluoroacetoxyacrylate with selectivities ranging from 9:1 (0 degreesC) to 15:1 (-78 degreesC).