Of D-glucofuranosidurono-6,3-lactones

V. Structure-Reactivity Correlations. Conformation of d-Glucofuranosidurono-6,3-lactones... 

Some long chain alkyl P-D-glycosides of D-glucofuranosidurono-6,3-lactone have been prepared by acid-catalysed glycosidation the glucuronides wa-e also reduced to alkyl p-D-glucofuranosides. ... 

Because of the particular structural features of compound 4, pointed out in Section I, the D-glucofuranosyluronic halide anomers not only have inverse thermodynamic stabilities with respect to those of D-glucopyranosyl halides but also show a different behavior towards alcohols. For instance, 2,5-di-O-acyl-a-D-gluco-furanosylurono-6,3-lactone halides, which are difficult to prepare, do not react with alcohols, inasmuch as an endo approach of the reagent is inhibited.14 The /3-bromides and -chlorides, however, just like /3-D-glucopyranosyl chlorides, are subject to alcoholysis, with formation of /3-D-glucofuranosidurono-6,3-lactones.16... 

Methyl cc-D-glucofuranosidurono-6,3-lactone (26) may be obtained exclusively by reaction of 4 with trimethyl orthoformate in the presence of boron trifluoride etherate.28 Its 2,5-dimethyl ether (27) is formed by methyl iodide-silver oxide methylation29,30 (Purdie-Ir-... 

Transacetalation of 5-O-substituted 1,2-O-alkylidene-D-gluco-furanurono-6,3-lactones is a reaction particularly suited to the synthesis of selectively protected D-glucofuranosidurono-6,3-lactones.34... 

Because direct glycosidation of 4 with phenols is not possible, indirect methods must be used for the preparation of aryl D-glucofuranosidurono-6,3-lactones (29). In addition, aryl 2,5-di-O-acetyl-D-glucofuranosidurono-6,3-lactones (30), obtained35-37 from the reaction of 1,2,5-tri-0-acetyl-D-glucofuranurono-6,3-lactones with phenols, can only be deacetylated by such multi-step procedures as (1) ammonolysis of 30 to afford aryl D-glucofuranosiduronamides (31), followed by amide hydrolysis and lactonization, 35,37 or (2) reduction of 30 with lithium aluminum hydride, and subsequent oxidation of the intermediate aryl D-glucofuranosides38 (32) (see Scheme 1). 

Esters of 4, which are used as substrates for the preparation of D-glucofuranosylurono-6,3-lactone halides (see Section 1,1) or aryl D-glucofuranosidurono-6,3-lactones (see Section 1,2), are prepared by reaction of 4 with acid halides or anhydrides in the presence of a basic or an acidic catalyst. 

Treatment of 25 and 26, respectively, in pyridine with equimolar amounts of benzyloxycarbonyl chloride at low temperature, followed by addition of an excess of ethoxycarbonyl chloride, yielded the corresponding methyl 5-0-(benzyloxycarbonyl)-2-0-(ethoxycarbonyl)-/3-(57) and -a-D-glucofuranosidurono-6,3-lactone (58). Hydrogenolysis of the benzyloxycarbonyl group resulted in formation of methyl 2-0-(ethoxycarbonyl)-/ - (59) (70%) and -a-D-glucofuranosidurono-6,3-lactone (60) (30%), respectively, both in crystalline form. The /3-D... 

Proton Coupling-Constants of Methyl fi- (25) and a-D-Glucofuranosidurono-6,3-lactone (26), and l,2-0-Isopropylidene-a-D-glucofuranurono-6,3-lactone (33)... 

The different reaction-periods needed57 for eliminations of the anomeric methyl D-glucofuranosidurono-6,3-lactones (see Table IV) must be attributed to differences in C-5-H acidity. For a possible explanation,89 it may be assumed that the electron-withdrawing property of the molecular vicinity also depends on the degree of electron... 

In a very thorough investigation of the reactions of hexaric acid lactones, and particularly dilactones, with sodium methoxide, F. Smith138,139 invariably obtained unsaturated products, at that time thought to be formed by isomerization and enolization. Hence, for alkyl D-glucofuranosidurono-6,3-lactones, also of bicyclic structure, similar reactions were believed24,25 to account for their unusual behavior in alkaline solutions. 

In order to decide whether compound 85 is formed from the (Z,E) or the (E,Z) conformer of 84, additional information appeared to be necessary. As depicted in Scheme 3, the transformations54 of methyl 5-0-benzyl-2-0-methyl-/3-D-glucofuranosidurono-6,3-lactone (86) to dimethyl (Z,E )-2-methoxy-5-(phenylmethoxy )-2,4-hexadienedioate (87) conclusively demonstrate that the site of the E disposition arises... 

The aryl aldofuranosides show a greater lability to alkali than the alkyl aldofuranosides. Phenyl 0-n-xylofuranoside is very labile to alkali.82 Treatment of 2-naphthyl 0-D-glucofuranosidurono-6,3-lactone with dilute alkali opens the lactone ring, and rapid hydrolysis occurs.40 Ishidate and Matsui81 noted that p-nitrophenyl 0-D-glucofuranosidur ono-6,3-lactone is most sensitive to alkali, the amide next, find then the pyranoid derivatives toward acids, the relative sensitivities of the lactone and the amide are reversed. 

The anomeric, methyl /3-D-glycoside lactone has also been synthesized by methylation of methyl /3-D-glucofuranosidurono-6,3-lactone.24 Trimethyl glucurone, formed by methylation of D-glucuronolactone with methyl iodide and silver oxide, is usually accompanied by some 2,5-di-O-methyl-A D-glucaro-b,3-lactone methyl ester ( trimethyl glucuralone ), an oxidation product. 

There are distinct correlations between the mechanism of formation of compound 43, the eliminations frequently observed with derivatives of aldaric acids, and the reducing power of alkyl D-glucofuranosidurono- and l,2-0-alkylidene-a-D-glucofuranurono-6,3-lactones toward complexed copper(II) solutions. These phenomena are discussed in Section VII. 

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