Showing papers on "Glucal published in 2003"
TL;DR: In this paper, a method for C-glycosidation with various silylacetylenes to d -glucal by iodine molecule via iodo-oxonium intermediates provided exclusively the α-acetylene glycoside products.
55 citations
TL;DR: In this paper, the conversion of glucal derived donor-acceptor cyclopropanes to acetals by TiCl4 mediated ring opening and alcohol trapping is described, and yields near 90% are consistently observed with aliphatic, benzylic and allylic alcohols, phenols and thiophenols.
42 citations
TL;DR: In this article, the 3,4,6-tri-tri O -acetyl-d -glucal in dichloromethane at 25°C in the presence of ZnCl 2 was obtained in 65-91% yields, with selective formation of the α-anomer.
39 citations
TL;DR: It is established that the configuration at C-5 of the piperidine ring plays a major role in controlling the stereochemical outcome and a short stereocontrolled synthesis of (+)-deoxoprosophylline is achieved using this chemistry.
Abstract: The synthesis of 3,4,6-tri-O-acetyl imino D-glucal 2 from D-glucal is reported. This imino glycal participates in a variety of Lewis acid mediated carbon–carbon bond forming reactions by allylic displacement of the C-3 acetate group by added nucleophiles. Allyl silanes, trimethylsilyl enol ethers, alkenes and dialkyl zinc reagents serve as suitable reaction partners. In all the cases studied, the β-anomer is predominant. Using imino glycal 8, epimeric at C-5, it is established that the configuration at C-5 of the piperidine ring plays a major role in controlling the stereochemical outcome. These results are rationalised by invoking the intermediacy of a conjugated N-acyliminium ion. A short stereocontrolled synthesis of (+)-deoxoprosophylline is achieved using this chemistry. Additionally, imino glucal 2 is transformed into bromo piperidine 16, whose X-ray crystal structure is determined. Bromide 16 participates in palladium catalysed Stille and Suzuki cross-couplings allowing access to C-2 substituted imino sugars 17 and 18. In other studies, imino sugar C-glycosides 21 and 22 are made by combining the Lewis acid mediated carbon–carbon bond forming reactions with stereospecific dihydroxylations.
31 citations
TL;DR: Propargylic and acetylenic silyl groups on propyne control the C-glycosidation products depending on the trimethylsilyl and triisopropylsilyL groups used.
28 citations
TL;DR: In this article, a one-pot C2-acetamidomannosylation reaction for the synthesis of 2-N-acetylamino-2-deoxy-α- d -mannopyranosides from glucals is described.
24 citations
TL;DR: Methyl N-acetyl-α-D-lividosaminide has been synthesized starting from 4,6-di-O-benzyl-Dglucal via a new nitro glucal derivative in six steps as mentioned in this paper.
20 citations
TL;DR: A nonclassical, totally stereoselective synthesis of orthogonally protected 1,3-disaccharides is reported, which smoothly gave the corresponding 2,2'-dideoxydisaccharide.
Abstract: A nonclassical, totally stereoselective synthesis of orthogonally protected 1,3-disaccharides is reported. Enantiomerically pure beta-keto-delta-lactones, efficiently obtained from glucal and galactal, are transformed into electron-poor heterodienes and chemo-, regio-, and stereoselectively cycloadded to glycals as electron-rich dienophiles, to directly afford 2-thiodisaccharides. The reductive desulfurization of the latter smoothly gave the corresponding 2,2'-dideoxydisaccharides.
16 citations
TL;DR: In this article, a simple four-step reaction sequence involving selective triflation and iodide displacement at C-2 was proposed for α-methyl glucopyranoside.
Abstract: 4,6-O-Benzylidene protected d -glucal, a useful synthetic intermediate, may be accessed from the extremely cheap and readily available starting material α-methyl glucopyranoside, via a simple four-step reaction sequence involving selective triflation and iodide displacement at C-2.
15 citations
TL;DR: The unique reactive intermediate formed in the 3,4,6,tri-O•O•benzyl•d−glucal−TfOH (triflic acid)-n•Bu4NI reaction system (in dichloromethane) reacted with nucleophiles in a regio-and stereoselective manner.
8 citations
TL;DR: In this article, a thermophilic and thermostable β-glycosyl hydrolase from the archeon Sulfolobus solfataricus and glucal or galactal as donors was used for the synthesis of 2-deoxy glycosides and, for the first time, of 2deoxygalactosides.
Abstract: The synthesis of 2-deoxyglycosides and, for the first time, of 2-deoxygalactosides is reported using a thermophilic and thermostable β-glycosyl hydrolase from the archeon Sulfolobus solfataricus and glucal or galactal as donors. The yields observed with alkyl acceptors confirmed that the robustness of the biocatalyst is of great help in designing practical syntheses of pure β-anomers of 2-deoxy derivatives of 4-penten-1-ol (obtained in 80% yield at 20 fold molar excess) and 3,4-dimethoxybenzyl alcohol (obtained in 19% yield at 3.3 fold molar excess). The attachment of 2-deoxyglyco units was performed on various pyranosidic acceptors (p-nitrophenyl α-d-glucopyranoside, o-nitrophenyl 2-deoxy-N-acetyl-α-d-glucosamine and p-nitrophenyl 2-deoxy-N-acetyl-β-d-glucosamine). At low molecular excesses of the acceptors, satisfactory yields (20-40%) of chromophoric 2-deoxy di- and trisaccharides were obtained. The different regioselectivity of our enzyme with respect to mesophilic counterparts reflects the importance...
TL;DR: In this paper, a method for C-glycosidation with various silylacetylenes to d -glucal by iodine molecule via iodo-oxonium intermediates provided exclusively the α-acetylene glycoside products.
Abstract: A convenient method for C-glycosidation (alkynylation) with various silylacetylenes to d -glucal by iodine molecule via iodo–oxonium intermediates provided exclusively the α-acetylene glycoside products. Eleven successful examples are shown under this condition.
TL;DR: In this article, a homogeneous endo-β-1,3-glucanase GA from Cellulomonas cellulans in an aqueous environment was used for enzymatic glycosylation of Dglucal.
Abstract: Enzymatic glycosylation of D-glucal was conducted by homogeneous endo-β-1,3-glucanase GA from Cellulomonas cellulans in an aqueous environment. Water-soluble β-1,3-glucan (laminarin) was used as a ...
TL;DR: In this paper, the synthesis of 3,4,6-tri-O-acetyl imino D-glucal 2 from D-Glucal is reported, where allyl silanes, trimethylsilyl enol ethers, alkenes and dialkyl zinc reagents serve as suitable reaction partners.
Abstract: The synthesis of 3,4,6-tri-O-acetyl imino D-glucal 2 from D-glucal is reported. This imino glycal participates in a variety of Lewis acid mediated carbon–carbon bond forming reactions by allylic displacement of the C-3 acetate group by added nucleophiles. Allyl silanes, trimethylsilyl enol ethers, alkenes and dialkyl zinc reagents serve as suitable reaction partners. In all the cases studied, the β-anomer is predominant. Using imino glycal 8, epimeric at C-5, it is established that the configuration at C-5 of the piperidine ring plays a major role in controlling the stereochemical outcome. These results are rationalised by invoking the intermediacy of a conjugated N-acyliminium ion. A short stereocontrolled synthesis of (+)-deoxoprosophylline is achieved using this chemistry. Additionally, imino glucal 2 is transformed into bromo piperidine 16, whose X-ray crystal structure is determined. Bromide 16 participates in palladium catalysed Stille and Suzuki cross-couplings allowing access to C-2 substituted imino sugars 17 and 18. In other studies, imino sugar C-glycosides 21 and 22 are made by combining the Lewis acid mediated carbon–carbon bond forming reactions with stereospecific dihydroxylations.
TL;DR: In this paper, the conversion of glucal derived donor-acceptor cyclopropanes to acetals by TiCl4 mediated ring opening and alcohol trapping is described, and yields near 90% are consistently observed with aliphatic, benzylic and allylic alcohols, phenols and thiophenols.
Abstract: The conversion of glucal derived donor–acceptor cyclopropanes to acetals by TiCl4 mediated ring opening and alcohol trapping is described. Good selectivity for the alpha anomer and yields near 90% are consistently observed with aliphatic, benzylic and allylic alcohols, phenols and thiophenols. The utility of this method to prepare oligosaccharides through intermediate O,S-acetals is illustrated.
TL;DR: In this paper, a one-pot C2-acetamidomannosylation reaction for the synthesis of 2-N-acetylamino-2-deoxy-α- d -mannopyranosides from glucals is described.
Abstract: A one-pot C2-acetamidomannosylation reaction for the synthesis of 2-N-acetylamino-2-deoxy-α- d -mannopyranosides from glucals is described. Glucal donors are activated by the reagent combination of 2,8-dimethyldibenzothiophene-5-oxide (DMDBTO) and trifluoromethanesulfonic anhydride. Upon subsequent addition of N-(TMS)acetamide and an appropriate glycosyl acceptor, the corresponding C2-acetamidomannopyranosides are formed.