- Investigating the rate of photoreductive glucosyl radical generation
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Chemical equations presented. The photoreduction of glucosyl halides to generate glucosyl radicals has been investigated to probe the nature of the photoredox cycle. Amine (the reductant) and catalyst concentration affect the reaction rate at low concentrations but exhibit saturation at higher concentrations. Water and hydrophobic catalysts were found to significantly increase the conversion efficiency.
- Andrews, R. Stephen,Becker, Jennifer J.,Gagne, Michel R.
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- Efficient stereoselective synthesis of α-C-glycopyranosides using 2,2'- azobis(2,4-dimethyl-4-methoxyvaleronitrile) [V-70]
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Efficient synthesis of α-C-glycopyranosides through a radical addition reaction using 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile) [V-70] as an initiator under mild condition was developed. This method made it possible to completely control the stereo
- Gotanda, Kentoku,Matsugi, Masato,Suemura, Miki,Ohira, Chiyo,Sano, Atsunori,Masahisa, Oka,Kita, Yasuyuki
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- A highly stereoselective synthesis of α-Linked C-glycopyranosides using 2,2'-azobis-(2,4-dimethyl-4-methoxyvaleronitrile) (V-70)
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α-Linked C-glycopyranosides were obtained effectively by the radical addition reaction using V-70, an effective radical initiator under mild conditions.
- Kita, Yasuyuki,Gotanda, Kentoku,Sano, Atsunori,Oka, Masahisa,Murata, Kenji,Suemura, Miki,Matsugi, Masato
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- Additive-controlled synthesis of 1- and 2-dexoysugars from thioglycosides
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Two photoreactions for the synthesis of 1- and 2-deoxysugars from thioglycosides were developed. In the presence of Hantzsch ester as an additive, a wide range of 1-deoxysugars were synthesized in moderate to excellent yields under irradiation with UV light without an exogenous photosensitizer. On the other hand, the utilization of 2,4,6-tri-tert-butylpyrimidine (TTBP) as the additive furnished a variety of 2-deoxysugars as the main products from their corresponding thioglycosides. The reported methodology has a broad substrate scope and high functional group tolerance and is scalable to gram-scale reaction.
- Gao, Chen-Fei,Wu, Biao,Wu, Xia,Xiong, De-Cai,Ye, Xin-Shan
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- NaBH3CN and other systems as substitutes of tin and silicon hydrides in the light or heat-initiated reduction of halosugars: A tunable access to either 2-deoxy sugars or 1,5-anhydro-itols
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UV light-promoted reduction of acetobromoglucose by NaBH3CN in t-BuOH afforded 1,3,4,6-tetra-O-acetyl-2-deoxy-α-d-arabino-hexopyranose in high yield and purity, via a Surzur-Tanner rearrangement, while, with 10 mol % thiophenol added, acetylated 1,5-anhydro-d-glucitol was cleanly obtained. Such tin-free and mild reductions, presumed to proceed via radical pathways, were more efficient with NaBH3CN compared to NaBH4 or NaBD 4, and do not occur with acetochloroglucose. Similar reductions to 1,3,4,6-tetra-O-acetyl-2-deoxy-α-d-arabino-hexopyranose were achieved upon heating to 80 C t-BuOH or CH3CN solutions of NaBH3CN and AIBN, but with a lower selectivity due to competing ionic reactions. With other pyranosyl bromides, reductions by NaBH3CN could be tuned similarly (d-galacto), but some (d-manno, 5-thio-d-xylo) gave mainly or exclusively 1,5-anhydro-itols. Other conditions, or reagents promoting SET process, afforded also reduced products, but with lower rates or selectivities. Primary iodides were reduced readily with NaBH3CN under UV light.
- Bruyère, Isabelle,Tóth, Zoltan,Benyahia, Hamida,Xue, Jia Lu,Praly, Jean-Pierre
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supporting information
p. 9656 - 9662
(2013/10/22)
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- Deoxygenation of carbohydrates by thiol-catalysed radical-chain redox rearrangement of the derived benzylidene acetals
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Five- or six-membered cyclic benzylidene acetals, derived from 1,2- or 1,3-diol functionality in carbohydrates, undergo an efficient thiol-catalysed radical-chain redox rearrangement resulting in deoxygenation at one of the diol termini and formation of a benzoate ester function at the other. The role of the thiol is to act as a protic polarity-reversal catalyst to promote the overall abstraction of the acetal hydrogen atom by a nucleophilic alkyl radical. The redox rearrangement is carried out in refluxing octane and/or chlorobenzene as solvent at ca. 130°C and is initiated by thermal decomposition of di-tert-butyl peroxide (DTBP) or 2,2-bis(tert-butylperoxy)butane. The silanethiols (ButO)3SiSH and Pr3iSiSH (TIPST) are particularly efficient catalysts and the use of DTBP in conjunction with TIPST is generally the most effective and convenient combination. The reaction has been applied to the monodeoxygenation of a variety of monosaccharides by way of 1,2-, 3,4- and 4,6-O-benzylidene pyranoses and a 5,6-O-benzylidene furanose. It has also been applied to bring about the dideoxygenation of mannose and of the disaccharide α,α-trehalose. The use of p-methoxybenzylidene acetals offers no great advantage and ethylene acetals do not undergo significant redox rearrangement under similar conditions. Functional group compatibility is good and tosylate, epoxide and ketone functions do not interfere; it is not necessary to protect free OH groups. Because of the different mechanisms of the ring-opening step (homolytic versus heterolytic), the regioselectivity of the redox rearrangement can differ usefully from that resulting from the Hanessian-Hullar (H.-H.) and Collins reactions for brominative ring opening of benzylidene acetals. When simple deoxygenation of a carbohydrate is desired, the one-pot redox rearrangement offers an advantage over H.-H./Collins-based procedures in that the reductive debromination step (which often involves the use of toxic tin hydrides) required by the latter methodology is avoided.
- Dang, Hai-Shan,Roberts, Brian P.,Sekhon, Jasmeet,Smits, Teika M.
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p. 1330 - 1341
(2007/10/03)
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- A novel and efficient method for the oxidative removal of O-benzyl protective groups of carbohydrates by tetrabutylammonium peroxydisulfate
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Various benzyl ethers of carbohydrates have been selectively oxidized to the corresponding benzoate esters 2a-j with tetrabutylammonium peroxydisulfate under neutral conditions followed by debenzoylation with sodium methoxide to afford the debenzylated carbohydrates 3a-j in good overall yields. Noteworthy is that highly chemoselective reactions were achieved with the co-existence of other functionalities. Thieme Stuttgart.
- Chen, Fen-Er,Peng, Zuo-Zhong,Fu, Han,Meng, Ge,Cheng, Yu,Lü, Yin-Xiang
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p. 627 - 628
(2007/10/03)
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- Reduction of activated ketals with borane-dimethyl sulphide
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Borane-Dimethyl sulphide reduces ketals activated with TMSOTf at -78°C in dichloromethane. The scope and selectivity of the reagent has been investigated.
- Hunter, Roger,Bartels, Birgit,Michael, Joseph P.
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p. 1095 - 1098
(2007/10/02)
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