- Pd(II)/PhI(OAc)2 promoted direct cross coupling of glucals with aromatic acids
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A highly efficient oxidative C2-aroyloxylation of D-glucal with aromatic carboxylic acids has been achieved for the first time using 5 mol% Pd(OAc)2 and 1 equiv of PhI(OAc)2 to produce C2-aroyloxyglycals in good yields. The use of excess of PhI(OAc)2 (2 equiv) provides C2-acyloxyglycal exclusively.
- Begum, Zubeda,Shankar,Sirisha,Reddy, B.V. Subba
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Read Online
- Glycosyl-Radical-Based Synthesis of C-Alkyl Glycosides via Photomediated Defluorinative gem-Difluoroallylation
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We have developed a stereoselective, glycosyl radical-based method for the synthesis of C-alkyl glycosides via a photomediated defluorinative gem-difluoroallylation reaction. We demonstrate for the first time that glycosyl radicals, generated from glycosyl bromides, can readily participate in a photomediated radical polar crossover process, affording a diverse array of gem-difluoroalkene containing C-glycosides. Notable features of this method include scalability, mild conditions, broad substrate scope, and suitability for the late-stage modification of complex molecules.
- Li, Cai-Yi,Ma, Yue,Lei, Zhi-Wei,Hu, Xiang-Guo
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supporting information
p. 8899 - 8904
(2021/11/20)
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- Pivaloyl-protected glucosyl iodide as a glucosyl donor for the preparation of β-C-glucosides
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A method for the selective synthesis of β-C-glucosides using α-D-tetra-O-pivaloylglucosyl iodide as a glucosyl donor is reported. Its diastereoselectivity differs from that of the respective acetyl-protected glucosyl bromide, as it reported in the literature under similar reaction conditions. The concentration of the catalyst, the solvent and the type of additive used are crucial factors that determine the reaction selectivity. This method has been applied in a short synthesis of dapagliflozin. The stability of α-D-tetra-O-pivaloylglucosyl iodide in CDCl3 and THF at reflux was also studied. All side products in the coupling and decomposition reactions were isolated and characterized, and possible pathways for their formation are proposed.
- Triantakonstanti, Virginia V.,Toskas, Alexandros,Iordanidis, Nicolaos S.,Andreou, Thanos,Koftis, Theoharis V.,Gallos, John K.
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supporting information
(2020/07/13)
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- Stereoselective Preparation of α- C-Vinyl/Aryl Glycosides via Nickel-Catalyzed Reductive Coupling of Glycosyl Halides with Vinyl and Aryl Halides
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Facile preparation of the α-C-vinyl and -aryl glycosides has been developed via mild Ni-catalyzed reductive vinylation and arylation of C1-glycosyl halides with vinyl/aryl halides. Good to high α-selectivities were achieved for C-glucosides, galactosides, maltoside, and mannosides, which were dictated by the employment of pyridine type ligands. As such, the present work represents unprecedented control for a high level of α-selectivity for C-vinyl-glucosides using cross-coupling approaches and offers hitherto optimal α-selective preparation of C-aryl glucosides via catalyst-controlled coupling strategies.
- Liu, Jiandong,Gong, Hegui
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supporting information
p. 7991 - 7995
(2019/01/04)
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- O-Glycosidation reactions promoted by in situ generated silver N-heterocyclic carbenes in ionic liquids
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We herein report O-glycosidation reactions promoted via silver N-heterocyclic carbene complexes formed in situ in ionic liquids. Seven different room temperature ionic liquids were screened for the glycosidation reaction of 4-nitrophenol with tetra-O-acetyl-α-d-galactopyranosyl bromide. Good to excellent yields were obtained using Ag-NHC complexes derived from imidazolium halide salts to promote the glycosidation reaction, whereas yields considered moderate to low were obtained without use of the silver carbene complex. Anion metathesis of the ionic liquids with inexpensive alkylammonium halides also resulted in silver N-heterocyclic carbene formation and subsequent O-glycosidation in the presence of silver carbonate. Effective utility of this methodology has been demonstrated with biologically relevant acceptors (including flavones and steroids) where O-β-glycoside products were obtained selectively in moderate to good yields. We have also demonstrated that the Ag-NHC complex is a superior promoter to traditionally used silver carbonate for the glycosidation of polyphenolic acceptors. The ionic liquids used in the study could be recycled three times without apparent loss in activity.
- Talisman, Ian Jamie,Kumar, Vineet,Razzaghy, Jacqueline,Malhotra, Sanjay V.
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experimental part
p. 883 - 890
(2011/06/20)
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- Cathode and medium effects on the electroreductive glucosidation of phenols
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The electroreductive pathway to phenol glucosidation, recently introduced by our research group, is analysed here in detail for both mechanism elucidation and choice of operating conditions. Preparative electrosyntheses were carried out on model substrates, varying either the cathode material, the supporting electrolyte, and/or the potential/current electrolysis conditions, to study their effects on the glucosidation yields and stereochemistry. Special care was devoted to the analysis of the reaction mixtures, leading to the identification and characterisation of several new products.
- Rondinini, Sandra,Mussini, Patrizia R.,Cantu, Giovanni,Sello, Guido
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p. 2989 - 2995
(2007/10/03)
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- Zinc-N-base mediated synthesis of pyranoid glycals mechanistic studies
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Reactions of acetobromoglucose 1 or acetylated 1-bromo-D-galactopyranosyl cyanide 3 with zinc dust in the presence of a N-base (1-methylimidazole, 4-methylpyridine, or triethylamine, pyridine, respectively) in ethyl acetate or benzene were efficiently inhibited by 10-30 mol % of 1,4-dinitrobenzene, elemental sulfur, or carbon tetrachloride. Presence of glycosyl radicals in these reactions was also shown by trapping them with tert-dodecyl mercaptan or methyl acrylate. Based on these observations and the high yielding formation of glycal derivatives 2 and 4 of high purity a free radical chain mechanism is proposed for the transformations.
- Somsak, Laszlo,Madaj, Janusz,Wisniewski, Andrzej
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p. 1075 - 1087
(2007/10/03)
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- Occurrence of phenylpyruvic acid in woody plants: Biosynthetic significance and synthesis of an enolic glucoside derivative
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The leaves and stems of Aspalathus linear is, a member of the Fabaceae, contains (Z)-2-(β-D-glucopyranosyloxy)-3-phenylpropenoic acid 1, an enolic glucoside of phenylpyruvic acid, representing the first unequivocal evidence for the latter's presence in woody plants. The synthesis of a derivative 2 of the natural product, and of related regiomeric and geometrical isomers 3,4 and 5, and the biosynthetic significance in relation to the shikimic acid pathway are discussed.
- Marais, Charlene,Steenkamp, Jacobus A.,Ferreira, Daneel
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p. 2915 - 2918
(2007/10/03)
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- Preparation of Unsaturated Carbohydrates by Ester Pyrolysis, II. - Thermal cis Eliminations from Completely Acetylated Aldopyranoses
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The pentaacetates 1, 2, 7, and 9 of β-D-glucose, α-D-mannose, β-D-allose, and β-D-galactose and the tetraacetates 13 and 18 of β-D-xylose and β-D-ribose eliminate when dissolved in acetone at temperatures about 350 deg C in a flow apparatus within 0.5 - 1 min regioselectively and stereoselectively the 1-O-acetate group.The respective anomers with trans-bound hydrogen in position 2 do not give this reaction corresponding to the pericyclic elimination mechanism.In a subsequent sigmatropic rearrangement the primarily formed 2,3,4,6-tetra-O-acetyl-1,5-anhydro-hex-1-enitols 3 (from 1 or 2), 8, and 10 as well as the 2,3,4-tri-O-acetyl-1,5-anhydro-pent-1-enitols 14 and 19 yield the α- or β-triacetyl-3-deoxy-hex-2-enopyranoses 4 or 5, 12 and the α- or β-triacetyl-3-deoxy-pent-2-enopyranoses 15 or 16, respectively.These products partially anomerize, e.g. 12 gives 11. - By further rearrangement with subsequent acetic acid anhydride elimination 5 and 16 are transformed into the enones 6 and 17. - 1,2,4,6-Tetra-O-acetyl-3-deoxy-β-D-threo-hex-2-enopyranose (12) is described for the first time.The 0H5(D)conformations of 11 and 12 are established by 13C NMR data.
- Koell, Peter,Steinweg, Eberhard,Meyer, Bernd,Metzger, Juergen
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p. 1039 - 1051
(2007/10/02)
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