Dominique Picq

Trifluoromethylation of sugar 1,4-lactones : Synthesis of 5-deoxy-5,5,5-trifluoro-D and L-ribose and lyxose derivatives

Abstract 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-trifluoro-2-ketoses with LiAlH 4 or NaBH 4 at an anomeric centre.

Stéréosélectivité comparée de la réduction de trifluorométhylcétones et des méthylcétones correspondantes: nouvelles voies d'accès à des dérivés trifluorométhylés de pentoses

Abstract The selectivity of the reduction of some trifluoroacetyl-1,3-dioxanes and 1,3-dioxolanes with DIBAH or L-Selectride was studied and compared with that of the corresponding methylketones; the results -in accordance with literature- show an important steric hindrance of the CF 3 group. The selectivity observed in these reductions led to good yields in the syntheses of 5,5,5-trifluorinated derivatives of D and L-pentofuranoses; a new method for the preparation of some functionalized trifluoromethylketones is described.

SYNTHESE DES 5-DESOXY-5,5,5-TRIFLUORO-D- ET -L-PENTOFURANOSES

ABSTRACT 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 LiA1H4 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.

Communication: An Improved Synthesis of Methyl 2,3-Anhydro-α and β-D-Lyxofuranosides

Methyl 2,3-anhydro-α (6) and β (7)-D-lyxofuranosides are important intermediates in the synthesis of C-3 substituted derivatives of D-arabinose which show biological activity as a tumor inhibitor.1,2 Some syntheses of 6 and 7 are reported but they are either expensive or give poor yields 3-4 and generally the authors refer to Baker and coll.5 who synthesized both α and β epoxides from D-xylose in five steps; yields were 28% and 22% respectively. This synthesis is very well described but reaction times and workups are long and several intermediates are distilled with difficulty under reduced pressure. Unger and coll.6, using Bakers method, improved the yield of compound 6 and Martin and coll.7 described a three steps synthesis of 6 but the final purification is very difficult and the use of mercuric reagents is not consistent with biological activity; furthermore these two publications concern only α anomer 6.

CATALYTIC DECOMPOSITION OF ALKYL CHLOROFORMATES BY HEXABUTYLGUANIDINIUM CHLORIDE

Abstract Hexabutylguanidinium chloride (0.5 molar %) efficiently decomposes alkyl chloroformates into chlorides, with low alkenes formation, via a SN2 mechanism as demonstrated from substituents effects and asymmetric chloride synthesis.

Synthese et equilibre thermodynamique des huit 5-O-benzyl-2- (ou 3)- dimethylamino-3 (ou 2)-O-mesyl-α (ou β)-D-xylo (ou arabino) - furanosides de methyle

Abstract Regioselectivity of the opening of 2,3-anhydrofuranosides 1 ( α and β ) and 2 ( α and β ) by dimethylamine (and by ammonia for 1 ) has been determined. Thermic stability of the eight corresponding vic -dimethylaminomesylates 11–14 ( α and β ) in CD 3 CN and C 6 D 6 has been studied by 1 H NMR : in each case steric hindrance seems to be the determinant factor of the four thermodynamic equilibria 11 ⇄ 12 ( α and β ) and 13 ⇄ 14 ( α and β ) ; aziridinium ions are assumed to be formed as intermediates and one of them has been effectively observed.

Silica-supported hexaalkylguanidinium chloride: a good heterogeneous catalyst for the decomposition of chloroformates

Abstract Silica-supported hexaalkylguanidinium (SiGCl), tetraalkylammonium (SiNCl) and tetraalkylphosphonium (SiPCl) chlorides were tested and compared for the obtention of chloroalkanes from chloroformates through a SN2 pathway. The superiority of SiGCl appears clearly from the collected data. Conversion times are largely dependent upon the morphology of the silica, but conditions quite close to those obtained with the hexabutylguanidinium chloride could be obtained; the decomposition of the 2-chlorooctyl chloroformate with SiGCl is apart, since there is a competition between the thermal SNi and the catalytic SN2 routes which could not be totally avoided.