Unsaturated derivatives

Fraser-Reid has summarized his own contributions to the chemistry of unsaturated sugars.  

A new review on the reactions of unsaturated sugars and their derivatives has appeared in two parts.  

A set of provisional recommendations for naming unsaturated sugar derivatives have been proposed by lUPAC-IUB, and a very extensive 

The recent literature on the synthesis and reactions of unsaturated sugar derivatives has been reviewed.  

These polyfluoroaryl groups enhance the acceptor properties of mercury and neutral 1 1 coordination complexes can be isolated with bipyridyl, 1,2-bis(diphenylphosphi-no)ethane, 1,10-phenanthroline, and so on [45, 63]. 

The olefin metathesis reaction as applied to carbohydrate dienes has been reviewed, as has the use of titanocene(III) and zirconocene(III) chlorides as mild reagents for generating 1-glycosyl radicals from glycosyl halides, and converting them into glycals.  

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Both saturated (50) and unsaturated derivatives (51) are easily accepted by lipases and esterases. Lipase P from Amano resolves azide (52) or naphthyl (53) derivatives with good yields and excellent selectivity. PPL-catalyzed resolution of glycidyl esters (54) is of great synthetic utiUty because it provides an alternative to the Sharpless epoxidation route for the synthesis of P-blockers. The optical purity of glycidyl esters strongly depends on the stmcture of the acyl moiety the hydrolysis of propyl and butyl derivatives of epoxy alcohols results ia esters with ee > 95% (30). 

Reactivity and yields are greatly enhanced by the presence of 0.5-1% Na in the Li. The reaction is also generally available for the preparation of metal alkyls of the heavier Group 1 metals. Lithium aryls are best prepared by metal-halogen exchange using LiBu" and an aryl iodide, and transmetalation is the most convenient route to vinyl, allyl and other unsaturated derivatives ... 

The only recorded example using this method in the sugar series is the chlorination of l,2 3,4-di-0-isopropylidene-D-galactopyranose (73) which affords in addition to the expected 6-chloro-6-deoxy derivative 74a, a 5,6-unsaturated derivative 75 as well. These products were separated by silica gel column chromatography no yields were given. 

N. A-Diethyl-2.3-dihydro-8//-thieno[2,3-r/]azcpin-7-amine (20), which is obtained in 49 % yield by photolysis of 6-azido-2,3-dihydrothiophene in a mixture of diethylamine and tetrahydro-furan. on treatment with bromine yields the fully unsaturated derivative 21.1,4... 

The fact that crosslinking proceeds at considerably high conversions of the monomers (50%) and at copolymerization temperatures > 60 °C is a distinctive feature of this system, as compared with systems containing other unsaturated derivatives of acrylic acids, which is determined by the difunctional nature of 10. 

Silyl enol ethers and ketene acetals derived from ketones, aldehydes, esters and lactones are converted into the corresponding o/i-unsaturated derivatives on treatment with allyl carbonates in high yields in the catalytic presence of the palladium-bis(diphenylphosphino)ethane complex (32). A phosphinc-free catalyst gives higher selectivity in certain cases, such as those involving ketene acetals. Nitrile solvents, such as acetonitrile, are essential for success. 

The 1,3-dipolar cycloadditions are a powerful kind of reaction for the preparation of functionalised five-membered heterocycles [42]. In the field of Fischer carbene complexes, the a,/ -unsaturated derivatives have been scarcely used in cyclo additions with 1,3-dipoles in contrast with other types of cyclo additions [43]. These complexes have low energy LUMOs, due to the electron-acceptor character of the pentacarbonyl metal fragment, and hence, they react with electron-rich dipoles with high energy HOMOs. 

Both the selenoxide and sulfoxide " reactions have been used in a method for the conversion of ketones, aldehydes, and carboxylic esters to their a, P-unsaturated derivatives (illustrated for the selenoxide). 

Among the carba-sugar derivatives, the most important and attractive members are amino carba-sugars, particularly 5a-carba- -D-glucopyran-osylamlne (validamine) and its unsaturated derivative (valienamine). These amino carba-sugars have been synthesized successfully, as well as validamycin antibiotics and some of the aforedescribed enzyme inhibitors. 

Selenoxides are even more reactive than sulfoxides toward (3-elimination. In fact, many selenoxides react spontaneously when generated at room temperature. Synthetic procedures based on selenoxide eliminations usually involve synthesis of the corresponding selenide followed by oxidation and in situ elimination. We have already discussed examples of these procedures in Section 4.3.2, where the conversion of ketones and esters to their a, (3-unsaturated derivatives is considered. Selenides can... 

The presence of the C15 saturated chain displayed an efficient gelling ability in a wide range of organic solvents, water, and protic solvent mixtures (1 1), whereas the unsaturated derivatives (mixture of four molecules) formed fibrous nanostructures as opposed to stronger gels. The diene and triene components of the cardanyl glycosides in their fully hydrated state formed fluid nanostructures at room temperature and could not self-assemble to form gels. 

The free reaction is rather slow (pseudo-first-order rate constant k = 4.8 x 10 6s 1, t1/2 ca. 2 days) and produces a mixture of the four possible Diels-Alder adducts 103a—d along with the byproduct 104. Note that all acids isomerize under the basic reaction conditions to give the a,/i-unsaturated derivatives 105a—d. 

The development of chiral hydrogenation catalysts for unfunctionalized alkenes also allows enantioselective hydrogenation of functionalized olefins where the functionality in the molecule is remote from the double bond. A series of oxazoline-, imidazoline- and pyridine-derived catalysts have been screened for the hydrogenation of unsaturated derivatives of vitamin E (Scheme 30.3). Hy-... 

In summary, based on the results of relatively limited studies, the dihydro beta-carboline, harmaline (80), is more active than either its fully unsaturated derivative harmine (79) or its reduced derivative tetrahydroharmine (81). The positional isomer of harmine, 6-methoxyharmalan (85), is slightly more potent than harmaline. Reduction to the tetrahydro derivative 86 reduces potency. Although thorough dose-effect studies have not yet been performed, none of the beta-carboline derivatives has been found to be significantly more potent than DMT (37). 

Unsaturated derivatives of saccharides in which fluorine is attached to sp2-hybridized carbon atoms have been synthesized by application of the Wittig reaction to sugars bearing a carbonyl group. For example,... 

In the course of investigations (175) on the structure of evemitrose, the corresponding 1,5-lactone 129, obtained upon oxidation of the sugar, yielded the a,/ -unsaturated derivative 130 when refluxed with methanolic potassium acetate. The same enonolactone 130 was obtained from L-mycar-ose (125c). 

K. S. Prickett, T. A. Baillie, Metabolism of Unsaturated Derivatives of Valproic Acid in Rat Liver Microsomes and Destruction of Cytochrome P450 , Drug Metab. Dispos. 1986, 14, 221 - 229. 

Scheme 3.11. Z Diastereoselectivities in conjugate additions of stannylcuprates to a,/ -unsaturated derivatives.

C-N.m.r. Data for Difluorinated Monosaccharides, Including Anhydro and Unsaturated Derivatives... 

The methods used for the preparation of these compounds can be divided into four groups (i) insertion of C-2 into a diamine, (ii) reduction of unsaturated derivatives, (iii) addition to the annelated C = C bond of quin-azolines, and (iv) cycloaddition. 

Diazoazoles, because of charge polarization and potential bifunctional reactivity of the derived betaine, react with dipolarophiles to give cycloaddition products. Generally all the diazoazoles react with electron-rich, unsaturated derivatives. The cycloaddition reaction with isocyanates is readily observed in the case of the reactive 3-diazopyrazoles, but it is much slower with other diazoazoles. By contrast, reaction with ylides and diazoalkanes is only observed for 3-diazopyrazoles and 3-diazoindazoles. 

It seems that initial stage of the treatment should be Knoevenagel reaction via the formation of unsaturated derivatives 1 (Scheme 3). This sequence is considered... 

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