Sugar-epoxide

Acid-catalysed sugar epoxide hydration has also been carrier) out in a few instances. Midler1207 1S0S and more recently Buchanan, ... 

The renowned sugar epoxide Brigi a anhydridehas Wn cleaved with a number of alcohols (Eq. 580) among them racthnnul ethanol, and benzyl alcohol.771... 

Among the numerous sugar epoxides which have been eubjected... 

Since the introduction of lithium aluminum hydride for the cleavage of sugar epoxides,M its use in this route to 3-deoxy sugars has become the method of choice. Thus, treatment of methyl 2,3-anhydro-4,6-0-benzyli-dene-a-D-mannopyranoside with lithium aluminum hydride affords methyl... 

T. D. Inch and G. J. Lewis, The synthesis of branched-chain, deoxysugars by sugar epoxide-Grignard reagent reactions, Carbohydr. Res., 15 (1970) 1-10. 

J. Stanek, Jr. and M. Cerny, A simple method for preparing water-soluble sugar epoxides using strong anion-exchange resin, Synthesis, (1972) 698-699. 

The new groups formed in these reactions are (rans-related, and the proportion of each isomer formed depends on the structure and stereochemistry of the parent sugar epoxide. When attached to rigid, six-membered... 

Other examples of related reactions have been summarized,24 and the cleavage of sugar epoxide derivatives with ammonia has been discussed in detail.26... 

Sometimes, it is possible to prepare sugar epoxides from ditosylates (Scheme 3.15b).83 For epoxide formation to occur, it is essential that one of the tosylates undergoes desulfonylation by S—O bond fission. Usually, this reaction occurs at the least hindered sulfonate. Then, the formed alkoxy will displace the remaining tosylate to provide the epoxide. Again, it is critical that the two reacting groups can attain a trans-diaxial relationship. 

Reduction of a sugar epoxide with lithium aluminum hydride also gives a mixture of deoxy sugars in which one isomer may preponderate. This method has been successfully used22 to synthesize a derivative (5) convertible into 2-deoxy-D-erythro-pentose-2(S)-d. 

Synthetic utilization of sugar epoxides with the use of known Wittig modifications has been shown to be very useful.92,99 Thus, the alkene 15a and its 3-O-benzyl analog were resynthesized,92 albeit in moderate yields, by the interaction of epoxides 236a and 236b, respectively, with triphenylphosphine in boiling N,N-di-methylformamide. 

Reactions leading to the formation of alkenic or a,/3-unsaturated bonds are very important in synthesis. This type of functionality is synthetically versatile, and of wide utility in the carbohydrate field. The use of sulfur reagents for conversion of sugar epoxides on vicinal disulfonates into al-kenes is well established97a 97b, and subsequent work with selenium reagents provided essentially comparable results. Thus, treatment of methyl 2,3-anhydro-4,6-0-benzylidene-a-D-mannopyranoside (219) with potassium selenocyanate in aqueous 2-methoxymethanol afforded methyl 4,6-0-benzylidene-2,3-dideoxy-a-D-ery/firo-hex-2-enopyranoside (220).27 Similarly, treatment of 5,6-anhydro-l,2-0-isopropylidene-a-D-glucofuranose (221) with potassium selenocyanate in methanol at room temperature... 

With sodium 0,0-dialkyl phosphorotelluronate, terminal epoxides are converted to alkenes very quickly, and cw-epoxides are reduced more easily than rraw5-epoxides (equation 31). The corresponding selenoate reagent has been applied to sugar epoxide deoxygenation (equation 32). 

Anhydrosugars Synthesis Sugar oxiranes 1,2-Sugar epoxides 1,6-Anhydrosugars Rearrangement... 

Anhydrosugars are also classified on the basis of the size of the heterocyclic anhydro ring. Thus, oxiranes (sugar epoxides), oxetanes, tetrahydrofuran, and tetrahydropyran derivatives are known. Reactivity of anhydrosugars is determined by the size of the heterocyclic anhy-... 

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