Radical trifluoromethylation of a d-mannose derived ketene dithioacetal. Synthesis of 2-C-tifluoromethyl derivatives of d-glycetr-D-galacto- and d-glycero-D-talo-talo-heptopyranose

摘要

Diacetone D-mannose was converted into ketene dithioacetals 3 by p Peterson reaction with 2-lithio- 2-(triethylsilyl)-1,3-dithiane or lithiobis(methylsulfanyl)methane. Radical addition of trifluoromethyl bromide (iodide) induced by electron transfer (from sulfoylate radical anion) led selectively to a dithioketalized 2-deoxy-2-C-(trifluoromethyl)-D-Galacto-heptopyrano- lactone (5a) or to the corresponding dithioketalized open sugar 9, mainly according to the alkylsulfanyl group.