RADICAL TRIFLUOROMETHYLATION OF A D-MANNOSE DERIVED KETENE DITHIOACETAL - SYNTHESIS OF 2-C-TRIFLUOROMETHYL DERIVATIVES OF D-GLYCERO-D-GALACTO-HEPTOPYRANOSE AND D-GLYCERO-D-TALO-HEPTOPYRANOSE

Diacetone D-mannose was converted into ketene dithioacetals 3 by a Pet erson reaction with 2-lithio-2-(trimethylsilyl)-1,3-dithiane or lithio bis(methylsulfanyl)(trimethylsilyl)methane. Radical addition of triflu oromethyl bromide (iodide) induced by electron transfer (from sulfoxyl ate radical anion) led selectively to a dithioketalized uoromethyl)-D- glycero-D-galacto-heptopyranolactone (5a) or to the corresponding dith ioketalized open sugar 9, mainly according to the alkylsulfanyl group. Reaction conditions were found for complete or partial dethioketaliza tion of these intermediates. A diisopropylidene-protected ifluoromethy l)-D-glycero-D-talo-heptopyranolactone (12) was obtained from 5a, with concomitant epimerization of C-2. Compound 9 was converted into eithe r the corresponding sugar 14 or its methyl thioglycoside 13. Most of t hese reactions gave preparative yields, and the overall sequence const itutes a three-step synthesis of -2-C-(trifluoromethyl)-D-glycero-D-ga lacto-heptose or D-talo-heptose derivatives.