Epoxides sugar

The main interest in epoxide sugars lies in the fact that on treatment with alkali the ring opens, with another Walden inversion, and two products... 

Epithio sugars acylation, 7, 171 hemiacetafs hydrolysis, 7, 170 Epitiostanol, 7, 182, 183 Epoxidations... 

TiPSON - COHEN Oleflnatlon Conversion o( sugar glycols via epoxides into sugar olefins. 

Alkylation of enamines with epoxides or acetoxybromoalkanes provided intermediates for cyclic enol ethers (668) and branched chain sugars were obtained by enamine alkylation (669). Sodium enolates of vinylogous amides underwent carbon and nitrogen methylation (570), while vicinal endiamines formed bis-quaternary amonium salts (647). Reactions of enamines with a cyclopropenyl cation gave alkylated imonium products (57/), and 2-benzylidene-3-methylbenzothiazoline was shown to undergo enamine alkylation and acylation (572). A cyclic enamine was alkylated with methylbromoacetate and the product reduced with sodium borohydride to the key intermediate in a synthesis of the quebrachamine skeleton (57i). 

Deoxy-D-jcylo hexose 6-(dihydrogen phosphate) (21) has also been synthesized (2) the reaction sequence makes use of 3-deoxy l 2,5 6-di-O-isopropylidene D-galactofuranose (16), a compound that can be easily prepared from D-glucose (2, 60). The mono-isopropylidene derivative (17) formed by partial hydrolysis of the di-ketal is converted into the 6-tosylate (18) by reaction with one molar equivalent of p-toluenesulfonyl chloride. From this the epoxide (19) is formed by reaction with sodium methoxide. Treatment of the anhydro sugar with an aqueous solution of disodium hydrogen phosphate (26) leads to the 6-phosphate (20)... 

The presence of hydroxyl groups in the benzylidene sugars does not interfere with the reaction and by-products are usually minor. Suitable solvents other than carbon tetrachloride, include benzene and tetra-chloroethane. Epoxide, amide, and other commonly encountered functionalities in sugar derivatives are unaffected under the reaction conditions. The corresponding 6-bromo-4-benzoates are valuable intermediates... 

Easily prepared from the appropriate monosaccharide, a glycal is an unsatu-rated sugar with a C1-C2 double bond. To ready it for use in potysaccharide synthesis, the primary -OH group of the glycal is first protected at its primary -OH group by formation of a silvl ether (Section 17.8) and at its two adjacent secondary - OH groups by formation of a cyclic carbonate ester. Then, the protected glycal is epoxidized. 

Enantioselective epoxidation of unfunctionalized alkenes was until recently limited to certain ds-alkenes, but most types of alkenes can now be successfully epoxi-dized with sugar-derived dioxiranes (see Section 9.1.1.1) [2]. Selective monoepox-idation of dienes has thus become a fast route to vinylepoxides. Functionalized dienes, such as dienones, can be epoxidized with excellent enantioselectivities (see Section 9.1.2). 

The last then-unknown carba-sugar, carba-) -DL-talopyranose pentaacetate (83), was synthesized from 36 as follows. Epoxidation of 36 with sodium methoxide gave, at the early stage of the reaction, the 2,3-epoxide... 

In a total synthesis of inhibitors of this kind, the following methods have so far been employed successfully (a) reaction of a cyclohexenyl halide with an amine, (b) coupling of an amine with an epoxide, and (c) condensation of an amine with ketone and reduction of the resulting Schiff base (reductive alkylation of an amino sugar). 

Conduritol Epoxides (1,2-Anhydroinositols) and Sugar-derived Epoxides. 364... 

C-branched sugars or C-oligosaccharides are obtainable through indium-promoted Barbier-type allylations in aqueous media.151 Indium-mediated allylation of a-chlorocarbonyl compounds with various allyl bromides in aqueous media gave the corresponding homoallylic chlorohydrins, which could be transformed into the corresponding epoxides in the presence of a base (Eq. 8.62).152... 

Vinyl epoxides are highly useful synthetic intermediates. The epoxidation of dienes using Mn-salen type catalysts typically occurs at the civ-olefin. Epoxidations of dienes with sugar-derived dioxiranes have previously been reported to react at the trans-olefin of a diene. A new oxazolidinone-sugar dioxirane, 9, has been shown to epoxidize the civ-olefin of a diene <06AG(I)4475>. A variety of substitution on the diene is tolerated in the epoxidation, including aryl, alkyl and even an additional olefin. All of these substitutions provided moderate yields of the mono-epoxide with good enantioselectivity. 

A paper concerning the synthesis of miharamycin analogues modified in the sugar moiety demonstrated the hydrolysis of a nitrile upon treatment with silica gel in the presence of water (Scheme 37).174 The cyanide 197 resulting from the opening of epoxide... 

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