Gerard Descotes

The use of N-alkoxycarbonyl derivatives of 2-amino-2-deoxy-d-glucose as donors in glycosylation reactions

1,3,4,6-Tetra-O-acetyl-2-alkoxycarbonylamino-2-deoxy-beta-D-glu copyranoses and 3,4,6-tri-O-acetyl-2-alkoxycarbonylamino-2-deoxy-alpha-D-glucopyra nosyl bromides have been used as donors in glycosylation reactions with model alcohols. beta-Glycosides were obtained in good yields and with a high degree of 1,2-trans stereoselectivity. An oxazolidinone was formed as the main product from the reaction of some of the glucopyranosyl bromides with alcohols of low reactivity, but the formation of all products could be interpreted by a strong participation of the alkoxycarbonylamino group.

Hydrogenation asymetrique de precurseurs d'aminoacides a l'aide de mono- et diphosphines derivees de sucres

Abstract Mono- and di-phosphines derived from sugars are synthesized and used as ligands in asymmetric catalysis. In the presence of a base (triethylamine, KOH…) the cationic complex [Rh(COD)dioxop] + ClO 4 − , catalyzes reduction of α-amino acid precursors with high optical yields (78–86%). The influence of the base is discussed.

Photohalogenation of glycopyranosyl halides: An expedient route to c-1 gem dihalogenated sugars

Resume Free-radical halogenation of peracetylated α and β-glycopyranosyl halides of 4C1-D chair conformation takes place at C-1 or C-5 with an α-stereoselectivity. However the less reactive α-chloride and bromide moieties at first undergo a dehydrohalogenation reaction. β-Chlorides when treated with N-bromosuccinimide give new C-1 gem chlorobromo sugars in 65–70 % yield while new C-5 halogenated compounds are obtained predominantly with β -fluorides or when chlorination is carried out with sulfuryl chloride SO2Cl2. The peracetylated C-1 gem chlorobromo derivative of gluco configuration can be cleanly dehydrobrominated to yield a C-1 chlorinated glucal. It also reacts chemio and stereoselectively in the presence of silver fluoride to give the corresponding new C-1 gem chlorofluoro or difluoro derivatives, either in 70 % yield, depending on the stoechiometry. All these new compounds exhibit a good to excellent stability. 19F- n.m.r. of three peracetylated 1-halogeno- β -D-glucopyranosyl fluorides shows that the JF,C3 coupling constants increase with the increasing electronegativity of the geminal axial halogen while JF,H decreases.

The relative stability of allyl ether, allyloxycarbonyl ester and prop-2 enylidene acetal, protective groups toward iridium, rhodium and palladium catalysts

Abstract The deprotection of allyloxycarbonyl derivatives of sugars was realized in the presence of allylether or prop-2-enylidene acetal with Pd(PPh 3 ) 4 or RhCl (PPh 3 ) 3 as catalyst while [Ir (COD) [PMePh 2 ) 2 ]PF 6 isomerized selectively the allyl ethers.

SYNTHESIS AND ITS STEREOCHEMISTRY OF AMINOPHOSPHONIC ACIDS DERIVED FROM 5-HYDROXYMETHYLFURFURAL

Abstract Some dialkyl N-substituted-α-amino-α-furylmethanephosphonates were synthesized via the addition of dialkyl phosphites to corresponding imines in mild conditions in a short time. When an imine is chirally N-substituted the reaction is stereoselective. Stereochemical aspects of the reaction in the light of Cram rules is discussed in this paper.

SYNTHESIS OF 1-AMINOALKANEPHOSPHONIC ACID DERIVATIVES CONTAINING FURAN MOIETY. PART II: FIRST SYNTHESIS OF (2-FURYL)AMINOMETHANE PHOSPHONIC ACID1

Abstract The synthesis of (2-furyl)aminomethanephosphonic acid from furfural via corresponding imine, dibenzyl ester and N-benzylsubstituted acid is presented. The synthesis was performed by the hydrogenolysis of a corresponding N-benzylsubstituted dibenzyl ester.

Derivatisation of 1,3,4,6-Tetra-O-Benzoyl-α-D-Fructofuranose at the Anomeric Site : O-Alkylation, O-Acylation, O-Arylation, Amination and Selenation Reactions

Abstract Treatment of D-fructose with benzoyl chloride gave either 1,2,3,4,6-penta-O-benzoyl-α-D-fructofuranose or 1,3,4,6-tetra-O-benzoyl-α-D-fructofuranose (lα) which with methanol, 2-nitrophenol, or 4-nitrophenol in the presence of the Mitsunobu reagents, diisopropyl azodicarboxylate and triphenylphosphine, gave the corresponding fructofuranosides in good yield; an analogous reaction with 4-methoxybenzylamine gave the corresponding D-fructo-furanosylamine. Alkylation with isopropyl alcohol or t-butyl alcohol was complicated by competition from transesterification and fructose disaccharide formation. There was little or no inversion in these reactions. The 2-O-acetyl derivative of 1 reacted with selenophenol and diethyl ether-boron trifluoride to give phenyl l-deoxy-3,4,6-tri-O-benzoyl-2-seleno-α,β-D-fructofuranose as a minor product and phenyl l,3,4,6-tetra-O-benzoyl-2-seleno-α,β-D-fructo-furanose which with tris(trimethylsilyl)silane and AIBN gave l,3,4,6-tetra-O-benzoyl-2,5-anhydro-D-mannitol and l,3...

Use of the Allyloxycarbonyl Protective Group in Carbohydrate Chemistry

Abstract Selective allyloxycarbonylation of primary hydroxyl groups was achieved by using allyl chloroformate as reagent. The allyl-oxycarbonyl group was removed selectively in the presence of the allyl protective group with the catalysts Pd(POS3)4 or RhCl-(Pφ3)3. Isomerisation of the allyl ether in the presence of the allyloxycarbonyl ester could be accomplished, albeit not completely selective, using [Ir(COD)(PMeφ2)2]PF6- Furthermore, the prop-2-enylidene dioxolane acetal was inert towards Pd(Pφ3)4 or RhCl(Pφ3)3 but was completely removed by PdCl2.

Nouvelle synthèse de spiro-orthoesters d-glucosidiques par photocyclisation stéréoselective d'hydroxyalkyl-d-glucosides

Abstract Irradiation of hydroxyalkyl glucosides in the presence of mercury(II) oxide and iodine gave glucosidic C-1-spiroorthoesters. Where the starting glycoside had CH2OH, the cyclization was regio- and stereo-specific by α-attack. The C-1-spiroorthoesters were readily available in a “one-pot synthesis” starting from glucosyl halides.

A new synthesis of 1,2-trans-2-acetamido-2-deoxyglycopyranosides via 1,2-trans-2-deoxy-2-iodoglycosyl azides

Abstract Trans -addition of iodoazide to the double bond of 3,4,6-tri- O -acetyl-1,5-anhydro- d - arabino -hex-1-enitol yielded 2-deoxy-2-iodoglycosyl azides, which are precursors of 1,2- trans -2-amino-2-deoxyglycopyranosides when treated by an alcohol in the presence of triphenylphosphine.