SYNTHESIS OF D-5-DEOXY-5,5,5-TRIFLUOROPEN TOFURANOSE AND L-5-DEOXY-5,5,5-TRIFLUOROPENTOFURANOSE

Synthetic pathways leading to 5-deoxy-5,5,5-trifluoropentofuranoses ar e reported. The main difficulty was to obtain a good diastereoselectiv ity at the C-4 carbon bearing the CF3 group. For the ribose and the ly xose derivatives the problem was partially solved by reacting trifluor omethyltrimethylsilane with 1,4-lactones of suitable glyconic acids le ading to hemiketalic 1-deoxy-1,1,1-trifluoro-2-ketoses. Reduction of t hese ketoses with NaBH4 or LiAlH4 allowed the desired configuration at the C-4 carbon. For the arabinose and the xylose derivatives it was f ound more convenient to synthesize uncyclised 1-deoxy-1,1,1-trifluoro- 2-ketopentoses by Dess-Martin oxidation of the corresponding protected alcohols. Highly selective reductions of these trifluoromethylketones led to arabino or xylo derivatives depending on the reducing agent.