Asymmetric 1,3-Dipolar Cycloaddition Reactions

Publisher Summary This chapter discusses the important reactions of the hydroxyl group. Knowledge of the relative reactivities of hydroxyl groups in carbohydrates is fundamental to a thorough understanding of carbohydrate chemistry. The chapter explains esterification, which forms the largest part of the literature since 1953 on selective reactions of carbohydrates. The common methods of esterification utilize an acid chloride or an acid anhydride as the reagent, but other acid derivatives often show different selectivities. An investigation pertinent to the subject of favored reactivity concerned the reactions of certain acyl halides with ethanol, in acetone or chloroform solution. The mixed-order nature of some of these reactions suggested that every rate-determining transition-state contained the substrate, the nucleophile (ethanol), and an acceptor— X—for hydrogen bonding, suitable acceptors being an acetone molecule, a chloride ion, or another ethanol molecule. The possibility that intramolecular hydrogen-bonding does not persist in pyridine and that the advantage of a bonded hydroxyl group would be lost, invalidates the explanation of favored reactivity. But if the hydrogen-bonding to pyridine is hindered in the transition state, intramolecular hydrogen-bonding could conceivably assume importance.

Relative Reactivities of Hydroxyl Groups in Carbohydrates

In the present perspective the advances and real possibilities of 1,3-dipolar cycloadditions as key steps in the total synthesis of virus inhibitors are described. Azides, nitrones, and azomethine ylides are the most appropriate 1,3-dipoles for the synthesis of privileged structures with the highest biological responses against viruses.

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1,3-Dipolar cycloadditions: applications to the synthesis of antiviral agents.

An improved procedure for the preparation of 2-isoxazolines

Publisher Summary This chapter provides an overview of the synthesis of branched-chain sugars. The naturally occurring, branched-chain sugars were classified as rare sugars until the 1960's, but the discovery of numerous new sugars as the glycosidic component of antibiotics during the past two decades has stimulated extensive research on their chemistry and biochemistry. Most of the branched sugars found in Nature have a polar substituent at the branching carbon-atom (Type A); tertiary alcohols are commonest, but some of them are in the form of a methyl ether, acetate, or cyclic carbonate and, in several instances, an amino or a nitro group is attached to the tertiary carbon atom. Diversity is observed in the branchings, but some of them are chemically interconvertible and also can be derived from a common intermediate. This chapter explains the concepts related to the nucleophilic reactions of sugar oxiranes, aldol addition, and cyclization of dialdehydes with nitroalkanes. It also presents a brief discussion on methyl-branched sugars and two-carbon-branched sugar.

https://www.jstage.jst.go.jp/article/yukigoseikyokaishi1943/40/9/40_9_778/_pdf

Synthesis of Branched-Chain Sugars

A new high-yielding route to branched-chain sugars of the streptose or the apiose type having at the branching point a configuration epimeric with that which would be obtained by the classical synthesis using Grignard reagents is described. The main steps are the preparation of branched-chain unsaturated cyano sugars by reaction of cyanomethylene triphenylphosphorane with keto sugars and the cis-dihydroxylation (KMnO4) of the so obtained cyano sugars. The cis and the trans isomers of a series of cyanovinylidenic sugars have been separated and the stereodependence of the long-range coupling constants in this class of compounds has been examined.

Utilisation d'ylides du phosphore en chimie des sucres VII. Synthèse de sucres ramifiés des types «streptose» et «apiose». Communication préliminaire

1.3-dipolar cycloaddition of alkenes (or alkynes) on sugars-nitriloxides and nitrilimines led respectively to 3-glycosyl-isoxazolines (or isoxazoles) and 3-glycosyl-pyrazolines (or pyrazoles). 5-glycosyl-isoxazolines were similarly prepared from arylnitriloxides and α- or ω-unsaturated sugars. These new C-glycosides are potential antiviral and anti-tumor agents.

C-glycosides III. Cyclo-additions dipolaires - 1,3 d'oxydes de nitriles et de nitrilimines. Communication préliminaire†‡

Ruthenium tetroxide oxidation of 1, 2-O-isopropylidene-β-D-threofuranose affords, besides the known 1, 2-O-isopropylidene-α-L-glycero-tetros-3-ulofuranose, a lactone. The tetrosulose is easily hydrated to the corresponding gem-diol whose dehydration on molecular sieves leads to a branched-chain dimer. Lead tetraacetate oxidation of 1, 2-O-isopropylidene-α-L-glycero-tetros-3-ulofuranose p-nitrophenylhydrazone leads quantitatively, to a gem-azoacetate, a new synthetic intermediate in carbohydrate chemistry. The 3-O-acetyl-1, 2-O-isopropylidene-α-L-glycero-tetr-3-enofuranose is easily obtained from the gem-diol. A highly stereoselective procedure is described to prepare the 3-O-acetyl-1, 2-O-isopropylidene-α-L-3, 4-exo-D2-erythrofuranose.

Chimie et pharmacologie de l'apiose III. Synthèse et propriétés de l'hydrate de l'O‐isopropylidène‐1, 2‐tétrosulo‐3‐furannose

D-glucal is selectively oxidised to the corresponding enone with a 60–80% yield by Fetizon's reagent (Ag2CO3-celite).

Oxydation allylique sélective en chimie des sucres au moyen du réactif de Fétizon. Note de laboratoire

The conformation of 34 branched-chain unsaturated sugars, prepared by reacting different Wittig reagents with a series of 1,2-O-isopropylidene-furannosul-3-oses, has been studied by PMR spectroscopy. The position of each compound in the flexible conformational cycle has been established by using the known stereo-dependence of the allylic coupling constants and checked with the other parameters of the spectra. An ‘isopropylidenic’ 4J2,4 coupling constant, present in all compounds whose H—C(4) is endo and absent in their C(4)-epimers has proved useful for configurational assignment at C(4).

Mme J. Tronchet

Papers

Utilisation d'ylides du phosphore en chimie des sucres VII. Synthèse de sucres ramifiés des types «streptose» et «apiose». Communication préliminaire

C-glycosides III. Cyclo-additions dipolaires - 1,3 d'oxydes de nitriles et de nitrilimines. Communication préliminaire†‡

Chimie et pharmacologie de l'apiose III. Synthèse et propriétés de l'hydrate de l'O‐isopropylidène‐1, 2‐tétrosulo‐3‐furannose

Oxydation allylique sélective en chimie des sucres au moyen du réactif de Fétizon. Note de laboratoire

Equilibres conformationnels de glucides au niveau de liaisons σ sp2sp3 CC. IV. Furannoses hybridés sp2 en C(3)