Reaction of 2,3-unsaturated aryl glycosides with lewis acids : a convenient entry to C-aryl glycosides
TL;DR: In this article, a facile synthesis of 2,3-unsaturated aryl glycosides by BF 3.Et 2 O mediated O to C transformation was reported.
About: This article is published in Tetrahedron Letters.The article was published on 1992-05-19. It has received 22 citations till now. The article focuses on the topics: Aryl & Lewis acids and bases.
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TL;DR: In this article, a new class of 2-C-formyl glycals, incorporating an α,β-unsaturated carbonyl system, have been proposed as potential synthons for numerous organic transformations.
44 citations
TL;DR: In this article, an approach to the regio-and stereocontrolled synthesis of aryl C- glycoside antibiotics is described, where the key reaction is the Lewis acid-mediated formation of 0-glycosides and its in situ conversion to C-Glycosides.
Abstract: An approach to the regio- and stereocontrolled synthesis of aryl C- glycoside antibiotics is described. The key reaction is the Lewis acid-mediated formation of aryl 0-glycosides and its in situ conversion to C-glycosides (0+C- glycoside rearrangement). The utility of this reaction is demonstrated in the total syntheses of vineomycinone B2 (1) and gilvocarcin M (2) and V (3). The latter synthesis established the absolute stereochemistry of the gilvocarcins.
39 citations
TL;DR: In this paper, a chiral pyrano[2,3-b] benzopyrans were synthesized by reaction of 2-C-acetoxymethylglycals 1 and 2 with phenols under Lewis acid catalysis.
37 citations
TL;DR: Various elimination procedures conducted on appropriate pyranoid and furanoid carbohydrate derivatives, especially on O-protected glycosyl halides afford cyclic vinyl ethers which Fischer (inappropriately) named glycals, form the major part of this chapter.
Abstract: Various elimination procedures conducted on appropriate pyranoid and furanoid carbohydrate derivatives, especially on O-protected glycosyl halides afford cyclic vinyl ethers which Fischer (inappropriately) named glycals. These are used extensively in general organic synthesis and for the preparation of non-carbohydrate natural products as well as biologically important complex carbohydrates and glycoconjugates. The best known member, tri-O-acetyl-D-glucal, is normally made from tetra-O-acetyl-alpha-D-glucopyranosyl bromide, is commercially available, and is used very frequently in this chapter to represent the family in examples of the reactions under discussion.
Because of the pronounced region- and stereoselectivities with which their addition reactions can be conducted, glycal derivatives are of major importance in synthesis. They also, however, take part in rearrangement processes that, likewise, have proved useful for synthesis. The principal one involves nucleophilic substitution of the allylic group with allylic rearrangement and results in products having double bonds in the 2, 3 positions and new substituents at the anomeric centers. By far the simplest and most commonly used way to this conversion involves the removal of the allylic substituent of the glycal and the generation of highly resonance-stabilized oxocarbenium ion intermediate. This may then react with nucleophiles at the anomeric center to give products as mixtures of diastereomers. Many examples and variations of this theme are described and form the major part of this chapter, but other ways are also considered
Almost no formal mechanistic studies have been carried out on the reactions in this chapter. Categorization of mechanism required for the treatment of this topic has been done on the basis of conditions used, product identification and largely, chemical intuition.
Keywords:
glycals;
transformation;
oxocarbenium ions;
regioselectivity;
diasterioselectivity;
nucleophilic substitutions;
homoallylic center;
addition-elimination reactions;
palladium;
leaving groups;
electrocyclic reactions;
unsaturated compounds;
free sugars;
glycosyl peroxides;
glycosyl caroxylates;
S-glycosides;
glycosyl halides;
glycosyl azides;
glycosyl phosphonates;
glycosyl hydrides;
furanoid glycols;
intramolecular applications;
reverse reaction;
reaction variations;
scope;
limitations;
configuration;
experimental procedures;
other methods
36 citations
TL;DR: Reaction of phenylmagnesium bromide with p-tert-butylphenyl 4,6-di-O-benzyl-2,3-dideoxy-beta-D-erythro-hex-2-enopyranoside in the presence of NiCl(2)(dppe) gave only the unsaturated beta-C-phenylglycoside 2abeta, while palladium-catalyzed reaction led to the preponder
Abstract: Treatment of p-tert-butylphenyl 4,6-di-O-benzyl-2,3-dideoxy-α-d-erythro-hex-2-enopyranoside (1aα) or the 4,6-di-O-(tert-butyldimethylsilyl) analogue (1bα) with various functionalized arylmagnesium bromides in the presence of a catalytic amount of PdCl2(dppf) at 25 °C in THF afforded the corresponding unsaturated C-arylglycosides 2−14 having the α-configuration in quite good yields. Benzyl-, allyl-, and vinylmagnesium bromides gave also the corresponding unsaturated α-C-glycosides 15−18, although in lower yields. When the same reaction was performed in the presence of NiCl2(dppe) as the catalyst at −40 °C, only the formation of the corresponding unsaturated C-arylglycosides having the β-configuration was observed. As expected, reaction of phenylmagnesium bromide with p-tert-butylphenyl 4,6-di-O-benzyl-2,3-dideoxy-β-d-erythro-hex-2-enopyranoside (1aβ) in the presence of NiCl2(dppe) gave only the unsaturated β-C-phenylglycoside 2aβ, while palladium-catalyzed reaction led to the preponderant formation of C-ph...
34 citations
References
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TL;DR: This chapter reviews recent advances in the chemistry and biochemistry of C-nucleosides, the literature concerning C-arylglycoside (i.e., nonnitrogen heterocyclic C- nucleoside) antibiotics, and recent significant advances in The most frequently used strategy for C-methine synthesis involves the construction of a heterocyClic aglycone from the C-1 substituent of a functionalized sugar intermediate.
Abstract: Publisher Summary This chapter reviews recent advances in the chemistry and biochemistry of C-nucleosides, the literature concerning C-arylglycoside (i.e., nonnitrogen heterocyclic C-nucleoside) antibiotics, and recent significant advances in the synthesis of C-nucleosides and C-glycosides. It also discusses biological test data and data that are relevant to structure–activity relationships. Modification of readily available natural C-nucleosides is an attractive route to new C-nucleoside analogs and derivatives, because one starting material often possesses much of the desired functionality and chiral properties. The chapter illustrates this approach with examples. The most frequently used strategy for C-nucleoside synthesis involves the construction of a heterocyclic aglycone from the C-1 substituent of a functionalized sugar intermediate.
179 citations
TL;DR: In this paper, Cp 2 HfCl 2 -AgClO 4 is particularly effective for this conversion, which leads to initial O-glycoside formation followed by rearrangement to C-congener.
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