Raoul Uzan

A new and direct access to glycono-1,4-lactones from glycopyranoses by regioselective oxidation and subsequent ring restriction

Abstract Treatment of partially protected or unprotected carbohydrates with the RhH(PPh 3 ) 4 -benzalacetone system leads exclusively to glycono-1,4-lactones by regioselective oxidation and subsequent ring restriction.

One-pot stereoselective synthesis of glycosyl azides via 1,2-cyclic sulfite

Abstract In a one-pot procedure, treatment of partially protected or unprotected aldoses with N,N ′-thionyldiimidazole and then, lithium azide leads stereoselectively to glycosyl azides.

Direct Regioselective Chlorination of Unprotected Hexitols and Pentitols by Viehe's Salt

Abstract Viehes salt allows the transformation of unprotected hexitols and pentitols into linear 1,6 and 1,5 dichloro derivatives in high yields. Usual competitive heterocyclization is minimized.

Direct regioselective chlorination of unprotected hexitols and pentitols by Vilsmeier and Haack's salt

Abstract Unprotected hexitols and pentitols are converted into 1,6 and 1,5 dichloro derivatives respectively, by Vilsmeier and Haacks salt in DMF.

A new route to C-glycosyl compounds. Wittig-type reaction promoted by zinc

In recent years, methods for the preparation of C-glycosyl compounds have become increasingly important in synthetic organic chemistry. These compounds are useful as subunits for the synthesis of biological active products’ and as potential enzyme inhibitors’. Significant attention has been focused on the development of new routes to prepare functionalized C-glycosyl compounds that are synthetic precursors of more complex C-glycosyl compounds. The starting materials can be furanose or pyranose carbohydrates, the main problem being the stereoselective introduction of a functionalized carbon atom at C-l. A widely used procedure to obtain carbon-carbon bonding at the anomeric position of carbohydrates was first reported by Zhdanov ef al. 3 This two-step procedure involves the formation of an unsaturated, open-chain intermediate, followed by a cyclization leading to the expected C-glycosyl compound. The first step is a Wittig reaction with protected furanose and pyranose hemiacetals. When stabilized ylides are used4, subsequent cyclization of the unsaturated intermediate may occur by treatment with bases or, sometimes, spontaneously. But when the Wittig reaction takes place with unstabilized ylides, the cyclization can be obtained by the iodoor mercuro-cyclization process’. It should be noted that C-glycosyl compounds can be synthesized in the same way when phosphonates are used instead of phosphorane

A stereoselective O-aryl glycosylation procedure via 1,2-cyclic sulfite

. Lastly, although stereoselective routes exist for both C-aand /I-glycosyl compounds, they mainly lack a general application. Stereoselectivity indeed depends on carbohydrate structures, ylides, and solvents. In the case of 2,3,4,6-tetra-O-benzyl-a,/?-D-glucopyranose (l), Nicotra et al.’ have observed an abnormal reaction of (carbethoxymethylene)triphenylphosphorane leading solely to a diene. The same elimination by Wittig reaction was observed for 3,4,6-tri-O-acetyl-2-O-benzyl-a&D-glucopyranose and partial elimination for 2,3,4,6-tetra-U-acetyl-a&D-glucopyranose. These abnormal reactions led Allevi et af.6 to use a Wittig-Horner reaction with 1 and sodium triethylphosphonoacetate

Réaction d'Ylures du soufre sur des sucres réducteurs: Application à la synthèse d'hydroxyméthyl C-glycosides.

In a one-pot procedure, treatment of partially protected D-glucose and unprotected D-xylose, with N,N″-thionyldiimidazole and then phenoxide ions gives stereoselectively β-O-aryl glycosides.

An efficient and facile three-step synthesis of 5-amino-5-deoxy-D-pentonolactams from unprotected D-pentono-1,4-lactones.

Abstract Treatment of reducing carbohydrates with unstabilized sulfur ylides affords epoxy alcohols. When the reaction is not accompanied by elimination of a leaving group at C-3, spontaneous cyclisation occurs, and hydroxymethyl C-glycosyl compounds are obtained.

Regioselective halogenation of pentono-1,4-lactones. Efficient synthesis of 5-chloro- and 5-bromo-5-deoxy derivatives

Abstract Regioselective bromination of D-pentono-1,4-lactones with SOBr 2 in DMF led to 5-bromo-5-deoxy derivatives. These intermediates were treated with LiN 3 and hydrogenated to give 5-amino-5-deoxy-D-pentonolactams in 60–83% overall yield.

A facile route to diastereomerically pure analogues of castanospermine and australine

Abstract Treatment of unprotected d -ribono, d -arabinono and d -xylono-1,4-lactones with either thionyl chloride or thionyl bromide in dimethylformamide led to 5-chloro- or 5-bromo-5-deoxy derivatives in 70%–95% yields. Under the same conditions, d -lyxono-1,4-lactone resulted in the 2-halogeno compounds.