Gérard Descotes

Syntheses photochimiques de dioxa-1,6 spiro[4.5] decanes pheromones de paravespula vulgaris L

Abstract A general approach to 1-6 dioxa[4.5]spirodecanes is presented and applied to the total synthesis of one pheromone of Paravespula vulgaris L.

Synthesis and some transformations of 1-azido-glycopyranosyl cyanides-precursors of anomeric α-amino acids

Abstract Acetylated 1-azido-glycopyranosyl cyanides (of the (1R)- 2, and (1S)- d -galacto 16, (1S)- d -arabino 5, (1R)- d -gluco 7, (1R)- 11, and (1S)- d -xylo 12 configurations) and C-(1- azido-1-deoxy- d -galactopyranosyl)formamide 19 were prepared from acetylated 1-halogeno- d -glycopyranosyl cyanides and formamide, resp., by sodium azide in dimethyl sulfoxide. Acetylated (1S)- 14 and (1R)- 15 1-chloro- d -galactopyranosyl cyanides were obtained from (1R)1- bromo- d -galactopyranosyl cyanide by lithium chloride in dimethyl sulfoxide. 1,3-Dipolar cycloaddition of azide ions to the cyano groups of 2 and 16 afforded acetylated 5-(1-azido-1-deoxy-α- and -β- d -galactopyranosyl)tetrazoles 3 and 17, resp., while that of dimethyl acetylene dicarboxylate to the azido moiety of 2 gave acetylated dimethyl 1-(1-azido-1-deoxy-β- d -galactopyranosyl)-1,2,3-triazole-4,5-dicarboxylate 20. Transformation of 3 by ethoxalyl chloride gave acetylated ethyl 2-(1-azido-1-deoxy-α- d -galactopyranosyl)-1,3,4-oxadiazole-5-carboxylate 21.

Octa-O-Acetyl-Sucrose: Regioselective Deacetylations by Lipolytic Enzymes

Abstract Treatment of octa-O-acetyl sucrose (1) with a lipolytic enzyme preparation from the yeast Candida cylindracea in aqueous buffer resulted in the predominant formation of 1′, 2, 3, 3′, 4, 6, 6′-hepta-O-acetyl-sucrose (2). Treatment of 1 with lipase from wheat germ afforded a minor amount of 1′, 2, 3, 3′, 4, 6-hexa-O-acetyl-sucrose (3) together with 2, 3, 3′, 4, 6-penta-O-acetyl-sucrose (4) as the major product. Effects of calcium ions, cosolvents, temperature and enzyme treatment on enzyme activity and selectivity were investigated. Results indicate that so called wheat-germ lipase is actually an esterase. Wheat germ lipase, immobilised on agarose, did not show appreciable activity on octa-O-acetyl-sucrose (1).

An efficient and stereoselective synthesis of 3,4,6-tri-O-acetyl-α-D- glucopyranose 1,2-[exo-alkyl orthoacetates]

The treatment of acetobromoglucose with N,N-dimethylformamide dialkyl acetals in the presence of tetra-n-butylammonium bromide affords the corresponding 1,2-exo-alkyl orthoacetates in a pure form and in almost quantitative yields.

Metathesis of Ω-unsaturated glucosides with chloro-aryloxide complexes of tungsten, as a new way leading to unsaturated bolaamphiphiles

Abstract Glucosides of unsaturated alcohols, bearing different protecting groups at glucose units underwent catalytic metathesis affording bolaamphiphiles with good yields. Tungsten aryloxo-complexes ( 1 and 2 ) were found to be superior catalysts for this process.

Heteromacrocycles from Ring-Closing Metathesis of Unsaturated Furanic Ethers

Abstract New 2,5-bis(unsaturated alkyloxymethyl)-furan led to macrocyclic furanic derivatives in the presence of Grubbs catalyst via dimerization or direct intramolecular metathesis according to the length of the sidearm.

Synthesis and structural characterization of macrocyclic carbohydrate derivatives obtained from catalytic metathesis reaction with chloro-aryloxide complexes of tungsten

Abstract Tungsten aryloxo-complex 1 catalyses the intramolecular metathesis reactions of di- and trisubstituted ω-unsaturated glucose, and glucosamine derivatives, yielding bicyclic carbohydrate-based compounds 12, 13, 14, 15 , containing 12-, and 14-atoms rings. Electrospray tandem mass spectrometry was used for the structural characterization of these novel bicyclic carbohydrate compounds.

Photolysis of sugar anomeric diazides: Sugar-derived tetrazoles as evidences for a major nitrene decomposition pathway

Abstract The preponderance of regioisomeric sugar-derived tetrazoles (up to 75% total yield) obtained upon photolysis of protected (benzyl, acetyl) glucopyranosylidene diazides, even in the presence of added acrylonitrile, proved that azidonitrene intermediates predominate over anomeric carbenes, in the reaction. Revisions are presented for its mechanism and one structure.

Photolysis of methyl 1-azido glucosides: unprecedented expansions of the pyranose ring under high stereocontrol

Abstract New structures arising from the photolysis of peracetylated methyl 1-azido-D-glucopyranosides account for the formation of excited intermediates which undergo stereocontrolled migrations of either the O-5 oxygen atom (a) or, competitively, the O-1 oxygen atom (b) or the C-2 carbon atom (c), depending, respectively, on the α or β orientation of the azido group in the substrate.

Additions comparées des halogenès sur le 3,4,6-tri-O-acétyl-1,5-anhydro-1,5-didésoxy-, d-arabino-hex-1-énitol et l'analogue 3,4,6-tri-O-benzylé; effets de solvant sur la formation spécifique des dérivés 1,2-didésoxy-1,2-dihalogéno-α-d-glucopyranoses

Abstract Comparison of the addition of chlorine and bromine to 3,4,6-tri- O -acetyl-1,5-anhydro-1,5-dideoxy- d - arabino -hex-l-enitol (1) and to the 3,4,6-tri- O -benzyl analog (2) shows a greater stereoselectivity for 2 in the formation of 1,2-dideoxy-1,2-dihalo-geno-α- d -glucopyranose derivatives. Stereospecific addition took place in nonpolar solvents, and a quantitative correlation was established between the polarity of the solvent and the stereospecificity of the addition of chlorine to 1 and 2 . Similar results were observed for the halogenomethoxylation of 1 and 2 .