Showing papers on "Glucal published in 1997"
TL;DR: In this article, a cyclopropanation of glycals 1, 2, 3, 4, and 41 was carried out using either dihalocarbene addition or zinc-carbenoid addition to yield 1,2-cyclopropanated sugars.
Abstract: Diastereospecific cyclopropanation of glycals 1, 2, 3, 4, and 41 was carried out using either dihalocarbene addition or zinc-carbenoid addition to yield 1,2-cyclopropanated sugars. Dichloro- and dibromocarbenes added stereoselectively anti to the C3 benzyloxy group, whereas (under Simmons−Smith conditions) the cyclopropanes were formed syn to the same substituent. The reactions of these 1,2-cyclopropanated sugars to provide either ring expanded glycosides or C2-branched chain glycosides were explored. Solvolytic ring expansion of 1,2-dibromocyclopropanated sugars with K2CO3 in refluxing methanol yielded the corresponding chiral oxepins 20−22. Electrophilic ring openings of parent cyclopropanes (14 and 17 derived from glucal 1) were carried out with different electrophiles to give functionalized 2-deoxy-2-C-branched chain glycosides. The ring openings of 14 in different solvents resulted in both α- and β-anomers, whereas 17 gave exclusively the α-anomer.
89 citations
TL;DR: The stereoselectivity of d-glucal derivatives with PhSCl and PhSeCl is dependent on the presence of an electronegative heteroatom substituent and the nature of the functionality at C(4) as discussed by the authors.
57 citations
TL;DR: In this article, the authors investigated the regioselectivity of the glycosylation reaction using p -nitrophenyl β-d -galactopyranoside, β- d -mannopyranoyl fluoride and d -glucal donors and acceptors.
53 citations
48 citations
TL;DR: The α-phenylthioglycoside (α-PHG) as mentioned in this paper exists both in solution and in the solid state in a 1C4 conformation, in which the C-2, C-3, c-4 and C-5 substituents are all axial.
35 citations
TL;DR: Stereospecific glycosylation via the Ferrier rearrangement catalyzed by iodine has been used to obtain both enantiomers of a trans 4-aryl-3-Hydroxy-2-azetidinone and convenient access has become available to all four homochiral stereoisomers of α-hydroxy-β-lactams some of which are synthons for Taxol and analogs.
33 citations
TL;DR: In this paper, the product distribution obtained in electrophilic reactions of Br2, N-bromosuccinimmide (NBS), tetrabutylammonium tribromide, TTRBLC, NBS-Et3N·3HF, ICl-NaN3 and MCPBA-KF with tri-O-benzyl-D-glucal in aprotic and protic solvents have been determined by NMR.
17 citations
TL;DR: The cycloaddition of dichloroketene to glucal followed by Baeyer-Villiger oxidation gave a bicyclic γ-lactone, an α-d -C- glucoside, which was further transformed to glucitol under the Suarez protocol as mentioned in this paper.
15 citations
TL;DR: In this paper, Naphthyl 3,4,6-tri tri -O-methyl-β-d -glucopyranoside was applied as a chiral auxiliary in an asymmetric Michael addition to the 2-O-crotonate.
Abstract: Naphthyl 3,4,6- tri -O- methyl-β- d -glucopyranoside , easily synthesized from tri -O- acetyl- d -glucal , has been applied as a chiral auxiliary in an asymmetric Michael addition to the 2-O-crotonate. A very high facial diastereoselection (>95%) was obtained. No diastereoselection was observed when 1,3,4,6- tetra -O- methyl-β- d -glucopyranoside was used as the chiral auxiliary. A stereochemical model, taking into account steric shielding and π-stacking effects, is proposed on the basis of the observed results.
14 citations
TL;DR: In the course of this study, it was revealed that the Pseudomonas lipase-catalyzed acetylation occurred in a high yield exclusively at the primary alcohols of three Ferrier rearrangement products derived from tri-O-acetyl-D-glucal.
Abstract: N-Acetyl-D-allosamine and its derivatives were synthesized from tri-O-acetyl-D-glucal based on lipase-catalyzed selective protection of primary alcohols, [3,3] sigmatropic rearrangement of allylic trichloroacetimidates, and stereoselective ruthenium-catalyzed dihydroxylation. In the course of this study, it was revealed that the Pseudomonas lipase-catalyzed acetylation occurred in a high yield (> 90%) exclusively at the primary alcohols of three Ferrier rearrangement products derived from tri-O-acetyl-D-glucal.
14 citations
TL;DR: In this article, a remarkable protecting group influence was observed in the base-induced reaction of protected halohydrins derived from d-glycals, and the tri-O-tert-butyldimethylsilyl (t-BuMe2Si)-protected halohydrin reacted with cesium carbonate in methanol at room temperature to give a mixture of epimeric formyl furanosides.
TL;DR: In this paper, the structures and compositions of soluble saccharide polymers were established by elemental analysis, 1H and 13C NMR, and FTIR spectroscopy.
Abstract: Unsaturated glucopyranose derivatives such as 1,2,3,4-tetra-O-acetyl-6-desoxy-β-D-xylo-hex-5-enopyranose (3) and 1,2,3,4-tetra-O-benzoyl-6-desoxy-β-D-xylo-hex-5-enopyranose (6), briefly called “Ac-exo-glucal (3)” and “Bz-exo-glucal (6)”, were synthesized. These exo-cyclic sugar vinyl ethers were investigated in polymerization reactions. The corresponding “saccharide polymers”, homo- and copolymers, were synthesized under free radical conditions. The structures and the compositions of the soluble “saccharide polymers” were established by elemental analysis, 1H and 13C NMR, and FTIR spectroscopy. Characterization of the polymers, like molecular weights and optical rotations are reported. Saccharide polymers with different sugar content and low as well as high molecular weights were obtained.
TL;DR: In this article, the preparation of 8-bromokalafungin (20) which is a key intermediate for the synthesis of C-glycoside containing pyranonaphthoquinone antibiotics related to medermycin (6) is described.
Abstract: The preparation of 8-bromokalafungin (20) which is a key intermediate for the synthesis of C-glycoside containing pyranonaphthoquinone antibiotics related to medermycin (6) is described. Although attempts to selectively monobrominate kalafungin (1) at C8 were unsuccessful, 8,10-dibromokalafungin (21) was prepared by using excess N-bromosuccinimide in chloroform. Selective bromination at C6 on a naphthalene ring was achieved upon treatment of naphthol (9) with N-bromosuccinimide (1 equiv.). Conversion of naphthol (9) into naphthoquinone (15) was effected by methylation, Baeyer–Villiger oxidation, acetylation via a Fries rearrangement and oxidation with ceric ammonium nitrate. Conversion of the 7-bromo quinone (15) into 8-bromokalafungin (20) proceeded through subsequent addition of 2-trimethylsilyloxyfuran (16) followed by oxidative rearrangement of the resultant furonaphthofuran (17) to furonaphthopyran (18). After reduction of the lactol (18) to cis ether (19), demethylation and epimerization at C5 with boron tribromide afforded 8-bromokalafungin (20). 8-Bromokalafungin (20) failed to undergo Pd(0)-mediated cross-coupling reactions with the stannyl glucal (22).
TL;DR: In this article, the preparation of 8-bromokalafungin (20) which is a key intermediate for the synthesis of C-glycoside containing pyranonaphthoquinone antibiotics related to medermycin (6) is described.
Abstract: The preparation of 8-bromokalafungin (20) which is a key intermediate for the synthesis of C-glycoside containing pyranonaphthoquinone antibiotics related to medermycin (6) is described. Although attempts to selectively monobrominate kalafungin (1) at C8 were unsuccessful, 8,10-dibromokalafungin (21) was prepared by using excess N-bromosuccinimide in chloroform. Selective bromination at C6 on a naphthalene ring was achieved upon treatment of naphthol (9) with N-bromosuccinimide (1 equiv.). Conversion of naphthol (9) into naphthoquinone (15) was effected by methylation, Baeyer–Villiger oxidation, acetylation via a Fries rearrangement and oxidation with ceric ammonium nitrate. Conversion of the 7-bromo quinone (15) into 8-bromokalafungin (20) proceeded through subsequent addition of 2-trimethylsilyloxyfuran (16) followed by oxidative rearrangement of the resultant furonaphthofuran (17) to furonaphthopyran (18). After reduction of the lactol (18) to cis ether (19), demethylation and epimerization at C5 with boron tribromide afforded 8-bromokalafungin (20). 8-Bromokalafungin (20) failed to undergo Pd(0)-mediated cross-coupling reactions with the stannyl glucal (22).
TL;DR: Vinyl glycoside 2, available in two steps from tribenzyl glucal, is found to be an excellent glycosyl donor for the synthesis of 2-deoxy-β-glycosides as mentioned in this paper.
Abstract: Vinyl glycoside 2, available in two steps from tribenzyl glucal, is found to be an excellent glycosyl donor for the synthesis of 2-deoxy-β-glycosides.