Trifluoromethylation of sugar 1,4-lactones : Synthesis of 5-deoxy-5,5,5-trifluoro-D and L-ribose and lyxose derivatives
摘要:
The four 5-deoxy-5,5,5-trifluoro-D and L-ribo and -lyxo furanoses were synthesized from lactones using CF(3)SiMe(3) in 5 or 6 steps and 30-40 % overall yield. The key step was a stereoselective reduction of 1,1,1-trifluoror-2-ketoses with LialH(4) or NaBH4 at an anomeric centre.
Synthese Des 5-Desoxy-5,5,5-Trifluoro-d- et -l-Pentofuranoses
摘要:
Synthetic pathways leading to 5-deoxy-5,5,5-trifluoropentofuranoses are reported. The main difficulty was to obtain a good diastereoselectivity at the C-4 carbon bearing the CF3 group. For the ribose and the lyxose derivatives the problem was partially solved by reacting trifluoromethyltrimethylsilane with 1,4-lactones of suitable glyconic acids leading to hemiketalic 1-deoxy-1,1,1-trifluoro-2-ketoses. Reduction of these ketoses with NaBH4 or LiAlH4 allowed the desired configuration at the C-4 carbon. For the arabinose and the xylose derivatives it was found 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.