Vilsmeier-haack reactoin of glycals-a short route to C-2-formyl glycals☆
TL;DR: A short and straightforward route has been accomplished for the synthesis of C-2-formyl glycals by a Vilsmeier-Haack reaction of glycals.
About: This article is published in Tetrahedron Letters.The article was published on 1991-07-29. It has received 52 citations till now. The article focuses on the topics: Glycal.
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TL;DR: In this paper, C-2-Methylene O- and C-glycosides are readily synthesized from C-acetoxymethyl glycals using Nafion-H®, montmorillonite K-10, LiClO4 (0.07m) in dichloromethane and Pd(PPh3)4 as catalysts.
38 citations
TL;DR: The Vilsmeier-Haack reagent can be used to form carbon-oxygen or carbon-nitrogen bonds, unless these are accompanied by formation of a carbon-carbon bond as mentioned in this paper.
Abstract: This chapter extends the discussion to reactions between the Vilsmeier-Haack reagent (subsequently referred to as the Vilsmeier reagent for brevity) and any other compounds in which a carbon-carbon bond is formed. The discussion thus excludes reactions in which the Vilsmeier reagent acts as a chlorinating agent (for example in the preparation of acid chlorides), or in which it forms carbon-oxygen or carbon-nitrogen bonds, unless these are accompanied by formation of a carbon-carbon bond. For a discussion of the nature of the reagent and of the mechanism of the reaction, the earlier chapter in vol. 49 should be consulted. There are also a number of reviews that deal at length with mechanisms of reactions involving the Vilsmeier reagent, notably those by Jutz and Marson, and hence this chapter will concentrate on applications, with brief mention of mechanisms when necessary.
Wizinger has pointed out that alkenes could react with the Vilsmeier reagent, but his only examples were styrenes where the intermediate carbocation has considerable stability.
Hydrolysis gives the cinnamaldehyde. In principle, any alkene which is not too sterically hindered can undergo this reaction, but the Vilsmeier reagent has low reactivity as an electrophile, and in practice activation is often necessary. The addition depends on the HOMO of the alkene, and anything increasing the HOMO energy will aid reaction, as for example further conjugation (dienes, trienes, etc.) or the presence of an electron-donating substituent. Hence aldehydes and ketones are active in their enol forms, and enol ethers and enamines are good substrates. Indeed, all additions covered by this chapter can be regarded as alkene additions, even those on active methyl groups attached to electron-deficient rings. As with any reaction involving carbocation intermediates, rearrangements are possible; the initial products are sometimes enamines, and this can give rise to polysubstitution. The substrates are grouped into eleven major subsections; references to reviews of particular relevance will be found in the appropriate subsection.
Keywords:
vilsmeier reaction;
non-aromatics;
alkenes;
dienes;
polyenes;
heteroatoms;
substituents;
enamines;
enamides;
alkynes;
aldehydes;
ketones;
imines;
hydrazones;
semicarbazones;
oximes;
carboxylic acids;
anhydrides;
acid chlorides;
esters;
lactones;
amides;
lactams;
imides;
nitriles;
methyl groups;
methylene groups;
adjacent rings;
comparison of methods;
experimental conditions;
experimental procedures;
tabular survey
36 citations
TL;DR: In this article, C-2 Methylene glycosides were synthesized from propargyloxymethyl glycals in a stereoselective manner using a catalytic quantity of AuCl3.
32 citations
TL;DR: Total synthesis now shows that the signature bicyclic framework assigned to orevactaene is a chimera; the compound is almost certainly identical with epipyrone A, whose previously unknown stereochemistry has also been established during this study.
Abstract: Orevactaene and epipyrone A were previously thought to comprise the same polyunsaturated tail but notably different C-glycosylated 4-hydroxy-2-pyrone head groups. Total synthesis now shows that the signature bicyclic framework assigned to orevactaene is a chimera; the compound is almost certainly identical with epipyrone A, whose previously unknown stereochemistry has also been established during this study. Key to success was the ready formation of the bicyclic core of putative orevactaene by a sequence of two alkyne cycloisomerization reactions using tungsten and gold catalysis. Equally important was the flexibility in the assembly process gained by the use of heterobimetallic polyunsaturated modules whose termini could be selectively and consecutively addressed in a practical one-pot cross-coupling sequence.
32 citations
TL;DR: A facile and efficient diastereoselective one-pot synthesis of polycyclic acetal-fused pyrano[3,2-c]pyrane-5(2H)-one and pyranopyrones demonstrated anticancer activities.
Abstract: A facile and efficient diastereoselective one-pot synthesis of polycyclic acetal-fused pyrano[3,2-c]pyrane-5(2H)-one was achieved through the annulation reaction of 2-C-formyl glycals with various 4-hydroxycoumarins and 4-hydroxy-6-methyl-2H-pyran-2-one. The asymmetric induction was significantly influenced by the C-4 stereogenic center of 2-C-formyl glycals. The resulting polycyclic acetal-fused pyranopyrones demonstrated anticancer activities.
32 citations
References
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146 citations
TL;DR: The Tetrasaccharid Lycotetraose, das im Tomatin with Tomatidin verknupft ist, lies sich strukturell aufklaren, indem 1. Tomatin, 2. Glykosid (β 1-Tomatin) and 3. das xylosefreie Trisaccharide Triscarid (Lycotriose), letzteres nach katalytischer Hydrierung zum Lycotriit, with Methyljodid and Silber
Abstract: Das Tetrasaccharid Lycotetraose, das im Tomatin mit Tomatidin verknupft ist, lies sich strukturell aufklaren, indem 1. Tomatin, 2. das daraus durch Abspaltung von D-Xylose gewonnene Glykosid (β1-Tomatin) und 3. das xylosefreie Trisaccharid (Lycotriose), letzteres nach katalytischer Hydrierung zum Lycotriit, mit Methyljodid und Silberoxyd in Dimethylformamid permethyliert wurden. Aus den Spaltstucken der permethylierten Verbindungen, die kristallisiert erhalten wurden, ergibt sich fur die Lycotetraose die verzweigte Konstitution einer β-D-Glucopyranosyl(1 2Glucose)-β-D-xylopyranosyl(1 3Glucose)-β-D-glucopyranosyl(1 4Galaktose)-α-D-galaktopyranose und damit fur das Tomatin die Formel I. Auch aus Demissin last sich, unter Abspaltung von D-Xylose und des Aglykons, kristallisierte Lycotriose gewinnen.
110 citations
TL;DR: Three fluoro-substituted unsaturated sugars have been synthesized by transformations within the D-glucal and ethyl 2,3-dideoxy-α-D-erythro-hex-2-enopyranoside series.
Abstract: Three fluoro-substituted unsaturated sugars have been synthesized by transformations within the D-glucal and ethyl 2,3-dideoxy-α-D-erythro-hex-2-enopyranoside series. A number of the intermediate unsaturated sugars not previously described have been characterized. The advantages of the t-butyldimethylsilyl blocking group in such syntheses are described.
71 citations
TL;DR: The palladium-catalyzed couplings of the protected 1-(tributylstannyl)-D-glucal 1 and substituted aryl bromides provide the corresponding C-arylglucals and a dimer as mentioned in this paper.
Abstract: The palladium-catalyzed couplings of the protected 1-(tributylstannyl)-D-glucal 1 and substituted aryl bromides provide the corresponding C-arylglucals and a dimer
70 citations
TL;DR: In this article, it was shown that triacetyl glucal can be converted to 6-O-triphenylmethyl ether or 6 O-benzoyl ester to promote solubility in chloroform, and the derivatives are oxidized in that solvent in 12 h or less.
Abstract: Whereas the pseudo-axial 3-hydroxyl group of allal derivatives is known to be inert to manganese dioxide oxidation, the equatorial counterpart in glucal derivatives is shown to be readily oxidized. Thus glucal is converted to the 6-O-triphenylmethyl ether or 6-O-benzoyl ester to promote solubility in chloroform, and the derivatives are oxidized in that solvent in 12 h or less.Acetonation of glucal is readily accomplished in 45 min using 2,2-dimethoxypropane and p-toluenesulfonic acid in dimethylformamide; the product may be oxidized directly either with manganese dioxide or dipyridine chromium oxide. Thus it is possible to obtain 1–3-g quantities of the crystalline acetonated enone from triacetyl glucal (via deacetylation, acetonation, and oxidation) in 3–4 h.If the acetonation medium stands for 2 h methyl 2,3-dideoxy-4,6-O-isopropylidene-α-D-erythro-hex-2-enopyranoside is obtained. The mechanism of its formation in the reaction medium is discussed.
64 citations