Benzylidene Acetal Research Articles

Chemo-, stereo- and regioselective hydrogenolysis of carbohydrate benzylidene acetals. Synthesis of benzyl ethers of benzyl α- d-, methyl β-D-mannopyranosides and benzyl α-D-rhamnopyranoside by ring cleavage of benzylidene derivatives with the LiAlH 4-AlCl 3 reagent

Treatment of benzyl α-( 1) and methyl β- d-mannopyranoside ( 2) with α,α-dimethoxytoluene gave the exo and endo isomers ( 3,5 and 4,6) of the dibenzylidene derivatives of 1 and 2. Hydrogenolysis of the exo isomers ( 3 and 5) with a molar equivalent of AlH 2Cl gave the 3-0-benzyl-4,6-0-benzylidene derivatives ( 7 and 21), whereas the endo isomers ( 4 and 6) gave the 2-0-benzyl-4,6-0-benzylidene compounds ( 8 and 22). The 2-0-allyl ether 9 of 7, the 3-0-allyl derivative ( 10) of 8 and compounds 21 and 22 were treated with an additional molar equivalent of AlH 2Cl at reflux and the products were the 4-0-benzyl-6-hydroxyl derivatives ( 11, 12, 23 and 24), whereas in the case of 22 the 6-0-benzyl-4-hydroxyl isomer ( 25) was also isolated. By deallylation of 11 and 12, 3,4-( 13) and 2,4-di-0-benzyl ( 14) ethers of 1 were prepared. Tosylation of 11 and 12, and subsequent reduction of the products ( 15 and 16) made possible the preparation of the partially protected benzyl α- d-rhamnopyranoside derivatives ( 17–20). The structures of the compounds synthesized were characterized by 1H and 13C NMR spectroscopic investigation and by chemical methods.

A novel, reductive ring-opening of carbohydrate benzylidene acetals, with unusual regioselectivity

A novel, reductive ring-opening of carbohydrate benzylidene acetals, with unusual regioselectivity

Quantitative treatment of lanthanide-induced shifts for some carbohydrate systems where chelation is observed

An approximate model (D) for the calculation of lanthanide-induced shifts or some trans-fused benzylidene acetals which chelate to shift reagents is described. Shifts calculated for the model system 4,5-dimethylveratrole using model D were in good agreement with the reported data. With the aid of model D, rotamer conformations of the methoxyl group on C-1 of methyl 4,6- O-benzylidene-3- O-methyl-α- d-mannopyranoside, methyl 3- O-benzyl-4,6- O-benzylidene-α- d-mannopyranoside, and methyl 4,6- O-benzylidene-α- d-mannopyranoside were investigated.

The 4,6-benzylidene acetals, and the conformation, of methyl α- d-idopyranoside

Methyl α- d-idopyranoside and its 2,3-dimethyl ether give only the known 4,6- O-( S)-benzylidene acetals on benzylidenation. Methyl α- d-idopyranoside 2,3-carbonate was prepared, and it gave a small proportion of the ( R)-benzylidene acetal, but, again, the ( S)-isomer was the main product. Surprisingly, in chloroform solution, methyl 4,6- O-( R)-benzylidene-α- d-idopyranoside assumes the 4C 1( d) conformation, having an axial phenyl group, rather than the 1C 4( d) form (which would have an equatorial phenyl group). The 4C 1 forms of the ( R) and the ( S) derivatives are stabilized by two hydrogen bonds that can be observed in their n.m.r. spectra. In the presence of water, methyl 4,6- O-( S)-benzylidene-α- d-idopyranoside is mainly in a skew form, but methyl α- d-idopyranoside exists as a mixture of the two chair forms. Several other compounds that have three or more axially attached oxygen atoms have been studied, but none were found to be in a skew form.

Synthesis of 4- O-α- d-galactopyranosyl- l-rhamnose and 4- O-α- d-galactopyranosyl-2- O-β-glucopyranosyl- l-rhamnose using dioxolane-type benzylidene acetals as temporary protecting-groups

The Halide ion-catalysed reaction of benzyl exo-2,3- O-benzylidene-α- l-rhamnopyranoside with tetra- O-benzyl-α- d-galactopyranosyl bromide and hydrogenolysis of the exo-benzylidene group of the product 2 gave benzyl 3- O-benzyl-4- O-(2,3,4,6-tetra- O-benzyl-α- d-galactopyranosyl)-α- l-rhamnopyranoside ( 6). Compound 2 was converted into 4- O-α- d-galactopyranosyl- l-rhamnose. The reaction of 6 with tetra- O-acetyl-α- d-glucopyranosyl bromide and removal of the protecting groups from the product gave 4- O-α- d-galactopyranosyl-2- O-β- d-glucopyranosyl- l-rhamnose.

Synthesis and 13C-NMR spectroscopic investigations of rhamnobioses

A convenient method has been developed for the synthesis of all mono- and di-O-benzyl ethers of methyl α-L-rhamnopyranoside applying a new stereoselective method for the hydrogenolytic ring-cleavage of benzylidene acetals. Using the prepared dibenzyl ethers as aglycones, the (1→2)-, (1→3)- and (l→4)-linked rhamnosyl-rhamnose derivatives ( 13– 15) were synthesised. Hydrogenolysis of the latter compounds and subsequent acetylation gave the pentaacetates ( 16– 18) of methyl dirhamnosides, which on saponification furnished the free methyl dirhamnosides ( 19– 21). Acetolysis of 16– 18 gave the corresponding dirhamnose-hexaacetates which were transformed into the three disaccharides by saponification. The structure of each product was investigated by 13C-NMR spectroscopy, and for the purpose of 13C-NMR studies the mono-O-methyl ethers of methyl α-L-rhamnopyranoside, the diacetates and di-O-benzyl ethers of the latter compounds, and, also the diacetates of methyl α-L-rhamnopyranoside were synthesised. It has been established that, for 13C-NMR investigations of oligosaccharides, the benzyl ethers of monosaccharides are more suitable model compounds than the currently used monosaccharide methyl ethers.

Gas chromatographic investigation of the exo and endo isomers of dioxolane ring benzylidene acetals of some carbohydrates

Gas chromatographic investigation of the exo and endo isomers of dioxolane ring benzylidene acetals of some carbohydrates

13C-N.m.r. relaxation times and chemical shifts of the exo and endo isomers of dioxolane-type benzylidene acetals of carbohydrates: determination of the absolute configuration

13C-N.m.r. relaxation times and chemical shifts of the exo and endo isomers of dioxolane-type benzylidene acetals of carbohydrates: determination of the absolute configuration

Transformations of cellobiose derivatives into analogues of lactose

The preparation of benzyl β-cellobioside 2,3,5,2′,3′-pentabenzoate ( 2b) via a 4′,6′-benzylidene acetal in 27% overall yield from cellobiose is described. This pentabenzoate has been utilised for conventional syntheses of the 6′-amino-, 4′-amino-, and 4′,6′-diamino-analogues of lactose, via the 4′,6′-dimesylate. In addition, reaction of the pentabenzoate 2b with sulphuryl chloride initially afforded the 6′-chloro derivative, which was then slowly transformed into a mixture of the 4′,6′,-dichloro-lactoside and an isomer in which the non-reducing ring of the disaccharide had been transformed into a 3′,6′-dideoxy-3′,6′-dichloro-gulopyranoside. The latter probably arose by neighbouring-group participation by the 3′-benzoyloxy group prior to the introduction of the secondary 3′-chloro substituent. The former dichloro compound was subsequently converted into 4′,6′-dideoxy-4′,6′-dichloro-lactose. It was found that the rate of nucleophilic displacement at C-4′ of a cellobioside was much lower than that for the corresponding α-linked disaccharide, maltose. Furthermore, nucleophilic displacement at C-4′ of a lactoside was accompanied by substantial elimination, to give the 4′ene, together with some cleavage of the inter-glycosidic bond. The origins of these effects are discussed.

Photoreactions of Cyclic Benzylidene Acetals with Ketones in the Presence and Absence of Dissolved Oxygen

Abstract Photoreactions of 2-phenyl-1,3-dioxane (1) and 4,6-O-benzylidene-1,2,3-tri-O-acetylglucopyranose (10) in the presence of benzophenone, acetophenone, or acetone have been studied in both deoxygenated and aerated benzene solutions at room temperature. Photolysis of 1 with ketone in deoxygenated solution gave a dimeric product of 1 (8), cross adduct, and pinacol, while in aerated solution an oxidative ring cleavage product, i.e., trimethyleneglycol monobenzoate (9), was obtained instead of 8, besides smaller amounts of pinacol and cross adduct. The yields of pinacol and cross adduct decreased with the change in ketone in the order benzophenone>acetophenone>acetone, while the yield of 8 or 9 was in the reverse order. Photolysis of 10 with ketone led to results parallel to those of 1: photolysis under nitrogen atomosphere gave pinacol, cross adduct, and a dimeric product of 10 (14), while under bubbling air 4-O-monobenzoate and 6-O-monobenzoate derivatives of 10 were obtained instead of 14, besides pinacol and cross adduct. The effects of temperature, oxygen, and structure on the course of the reaction, to produce dimeric or ring opening products, have been discussed.

Some benzylidene acetal derivatives of theophylline nucleosides

The reaction of some hexopyranosyltheophylline nucleosides with benzaldehyde in the presence of zinc chloride gave the expected benzylidene acetals. Thus, 7-α-d-mannopyranosyltheophylline gave the 2′,3′:4′,6′-diacetal as a mixture of diastereo-isomers, one of which was isolated. The β-d-galacto- and β-d-gluco-pyranosyltheophyllines gave the 4′,6′-acetals, which were characterised as 2′,3′-diesters. Mild, acidic hydrolysis of 7-(4,6-O-benzylidene-2,3-di-O-mesyl-β-d-glucopyranosyl)theophylline gave 7-(2,3-di-O-mesyl-β-d-glucopyranosyl)theophylline, and strongly basic hydrolysis gave 7-(2,3-anhydro-4,6-O-benzylidene-β-d-allopyranosyl)theophylline. Ring-opening of this 2′,3′-epoxide with iodide anion afforded mainly 7-(4,6-O-benzylidene-2-deoxy-2-iodo-β-d-altropyranosyl)theophylline, which was characterised as the 3′-acetate.

ChemInform Abstract: OXIDATION OF BENZYLIDENE ACETALS BY OZONE

AbstractDieOxidation des Dioxolans (I) mit Ozon gibt das Benzoylderivat (IIa) neben dem Isomeren (IIb); letzteres entsteht erst sek. durch Äquilibrierung von (IIa).

Oxidation Of Benzylidene Acetals by Ozone

Oxidation of five-membered ring (1,3-dioxolan) and six-membered ring (1,3-dioxan) benzylidene acetals by ozone are reported.

Synthetic approaches to kasugamine

Reactions are described that lead to an immediate, chemical precursor of kasugamine the amino-sugar component of the aminocyclitol antibiotic kasugamycin. The key reaction involved the introduction of a bromine atom by a stereoselective ring-opening of a benzylidene acetal.

Reactions of Nitro Sugars. XXVI. Analysis and Separation of Stereoisomers by Nuclear Magnetic Resonance Spectroscopy and Column Chromatography of Benzylidene Derivatives

Stereoisomeric methyl 4,6-O-benzylidene-3-deoxy-3-nitrohexopyranosides proved to be distinguishable by the chemical shifts of their benzylidene methine proton signals, and ratios of such isomers in mixtures could be estimated by signal integration. The method was applied to a reinvestigation of the epimeric distributions in which methyl 3-deoxy-3-nitro-α-D-hexopyranosides arise, firstly, in the nitromethane cyclization of 2-O-[(S)-formyl(methoxy)methyl]-(R)-glyceraldehyde and, secondly, in their base-catalyzed configurational equilibration via nitronates. Previous results were essentially confirmed as far as the preferred configurations are concerned but require some revision as to the relative abundance of less favored configurations. By preparative chromatography of benzylidene acetals and subsequent debenzylidenation, some nitrohexopyranosides of the a-D series were isolated for the first time in crystalline condition. Separation of isomers in the β-D series was improved by use of chromatography and by a new method involving differential reactivities of compounds toward alkali.

Chemistry of 1-(dimethylamino)ethylidene and α-(dimethylamino)benzylidene acetals: utility as blocking group for diols and for selective esterification.

Chemistry of 1-(dimethylamino)ethylidene and α-(dimethylamino)benzylidene acetals: utility as blocking group for diols and for selective esterification.

Oxidation of carbohydrates with chromium trioxide in acetic acid. II. Acetals. A new synthesis of ketoses

Oxidation of fully acylated methylene and benzylidene acetals of alditols with chromium trioxide in acetic acid yields fully acylated ketoses in their keto form. Derivatives of hex-3-uloses have been prepared by this method. Syntheses of 3,4-O-methylene-D-mannitol and 3,4-O-methylene-D-glucitol are described.

The facile bromination by N-bromosuccinimide of benzylidene acetals of carbohydrates. Application to the synthesis of 2,6-imino carbohydrates (substituted 2,5-oxazabicyclo[2.2.2]octanes).

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFacile bromination by N-bromosuccinimide of benzylidene acetals of carbohydrates. Application to the synthesis of 2,6-imino carbohydrates (substituted 2,5-oxazabicyclo[2.2.2] octanes)Theodore L. Hullar and S. B. SiskinCite this: J. Org. Chem. 1970, 35, 1, 225–228Publication Date (Print):January 1, 1970Publication History Published online1 May 2002Published inissue 1 January 1970https://doi.org/10.1021/jo00826a046RIGHTS & PERMISSIONSArticle Views528Altmetric-Citations44LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (607 KB) Get e-Alerts Get e-Alerts

Mass-spectrometric study of carbohydrates: Benzylidene acetals of alditols

The mass spectra of benzylidene acetals of various alditols have been measured. An interpretation of the fragmentation processes is presented. The molecular weight can readily be obtained, since a molecular ion is formed. It is possible to relate the characteristics of the mass spectra to the structure and configuration of the compounds studied.

617. Aspects of stereochemistry. Part XXII. Structure, conformation, and absolute configuration of some carbohydrate benzylidene acetals containing fused ring systems

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