Ketones carbohydrate-derived

These ketones can also be used in kinetic resolutions.107 The carbohydrate-derived ketones have been used in conjunction with acetonitrile and H202. The reactions are believed to proceed through dioxiranes generated by a catalytic cycle involving a peroxyimidic acid.108... 

In an approach to the potent calcium antagonist, diltiazem (11), a BINOL-derived ketone (12) was found to provide higher ee than when a carbohydrate-derived ketone was used to prepare the epoxide 13 (Scheme 9.16).123... 

As shown above, many of the methods that are available to form carbon-carbon bonds rely on the reaction of a carbanion with a suitable electrophile. Keto-sugars are readily available by simple oxidation of hydroxyl groups. Thus, the reaction of carbohydrate-derived ketones or aldehydes with carbanions has been extensively explored. However, keto groups are suitable substrates in olefinations, such as Wittig reactions, leading to versatile intermediates for the construction of complex structures. This section will detail some application of keto-sugars in total syntheses along these two main lines. 

Carbohydrate-derived ketones are versatile intermediates in organic synthesis. Thus, l,2 5,6-di-G-isopropylidene-a-D-nh( -hex-3-ulofuranose (2b) has been extensively used. Due to steric hindrance of the 1,2-0-isopropylidene group and conformational restrictions,nucleophiles of choice attack preferentially the P-face (ii-face) of the... 

The use of pyridinlum chlorochromate as a reagent for the oxidation of alcohols to aldehydes and ketones (including carbohydrate ketones) has been reviewed, and a review in Japanese on nucleophilic additions to carbohydrate-derived ketones has been 2... 

Several novel carbohydrate-derived ketones have been reported. Arabinose-derived ketone catalyst 16a has been shown to provide good enantioselectivities for the epoxidation of trans-aliphatic alkenes but offered poor enantioselectivity for cis-alkenes [69-71]. Studies found that increased enantioselectivities could be achieved for the epoxidation of dx-alkenes with decreased size of the acetal blocking groups. The best results for the epoxidation of ds-alkenes were found with methoxy catalyst 16b, which was successfully used in the synthesis of the side chain of Taxol [72]. 

The word carbohydrate derives historically from the fact that glucose, the first simple carbohydrate to be obtained pure, has the molecular formula C6H,206 and was originally thought to be a "hydrate of carbon, C6(Tl20)6." This view was soon abandoned, but the name persisted. Today, the term carbohydrate is used to refer loosely to the broad class of polyhydroxvlated aldehydes and ketones commonly called sugars. Glucose, also known as dextrose in medical work, is the most familiar example. 

Carbohydrate-derived methyl ketone enolates show absolutely no induced diastereosclcctivity with respect to aldehydes see ... 

S. David and A. Thieffry, The bromiaolysia reaction of staanylene derivatives A icgiospedfic synthesis of carbohydrate-derived hydroxy-ketones, J. Chan. Soc. Perkin Trans. 3 1568 (1979). 

In 1993, Enholm described the Sml2-mediated aldol reactions of ot-benzoyl lactones derived from carbohydrates with ketones.153 For example, treatment of lactone 136 with Sml2 in the presence of (+ )-dihydrocarvone 137 gave aldol adduct 138 in good yield and in high diastereoisomeric excess (Scheme 5.97). In this example, HMPA is used as an additive to increase the reduction potential of Sml2 and thus to facilitate Sm(III) enolate formation from the ot-benzoyl lactone.153... 

Carbohydrates are the most abundant of all organic compounds in the biosphere. Many members of the carbohydrate class have the empirical formula Cx(H20)y, and are literally hydrates of carbon. The fundamental units of the carbohydrate class, the monosaccharides, are polyhydroxy aldehydes or ketones and certain of their derivatives. As with other classes of biologically important compounds, much of the function of the carbohydrates derives from the ability of the monosaccharides to combine, with loss of water, to form polymers oligosaccharides and polysaccharides. The chemistry of carbohydrates is, at its core, the chemistry of carbonyl and hydroxyl functional groups, but these functional groups, when found in the same compound, sometimes exhibit atypical properties. The discussion that follows is designed to review the aspects of carbohydrate chemistry that are especially important for isolation, analysis, and structure determination of biologically important carbohydrates. 

An oxidation where this system is superior is in the reaction of carbohydrate derivatives where it is notably better than the acetic anhydride method, mainly due to the shorter reaction times, e.g. the preparation of the ketone (14 equation 7) ... 

Finally, carbohydrate ligands of enantioselective catalysts have been described for a limited number of reactions. Bis-phosphites of carbohydrates have been reported as ligands of efficient catalysts in enantioselective hydrogenations [182] and hydrocyanations [183], and a bifunctional dihydroglucal-based catalyst was recently found to effect asymmetric cyanosilylations of ketones [184]. Carbohydrate-derived titanocenes have been used in the enantioselective catalysis of reactions of diethyl zinc with carbonyl compounds [113]. Oxazolinones of amino sugars have been shown to be efficient catalysts in enantioselective palladium(0)-catalyzed allylation reactions of C-nucleophiles [185]. 

S. David and A, Ihieffiy, The btominolysis reacrion of staimylene derivatives A regiospecific syndiesis of carbohydrate-derived hydroxy-ketones, J. Chem. Soc. Perkin Thins. 7 1568 (1979). A. Lubineau, H. Arcostanzo, and Y. Quenefti, Stereochemical study of cycloadditions using erythrose and threose based dienes as sources of 2-nonulosonic acid analogs, J. Carbokydr. Chem. 14 1301 (1995). 

More interest has been shown in the past year in the laser-induced processes involving organic molecules. One such study is the laser irradiation (193.3 nm) of the ketones (1-4). This study has shown that the Norrish Type I process is dominant resulting in a-fission and the formation of alkyl and acyl radicals. The ultimate products formed are alkanes and carbon monoxide. Norrish Type I reactivity is also observed in more complex molecules such as the carbohydrate derivatives (5) and (6). Irradiation of these in solution again brings about a-cleavage to give the isomeric radicals ]) ... 

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