W.G. Overend

A study of ruthenium tetroxide as an oxidant for alcohols

Abstract The oxidation of benzhydrol and partially protected sugars with ruthenium tetroxide has been studied and the stoichiometry of the reaction verified. Axial and equatorial hydroxyl groups on an otherwise protected pyranoid ring are oxidized with equal ease. The generation of the tetroxide with periodate and ruthenium dioxide has been confirmed to be an easy reaction, providing that the dioxide has been prepared by the precipitation process.

The preparation of amino sugars from methyl glycopyranosiduloses: methyl 4-acetamido-4,6-dideoxy-a-α-L-talopyranoside

A route to derivatives of amino sugars from partially protected glycopyranosides by sequential oxidation to the corresponding glycopyranosidulose, oximation, and reduction of the oxime has been extended by the conversion of methyl 6-deoxy-2,3-O-isopropylidene-α-L-mannopyranoside into derivatives of a 4-amino-4,6-dideoxy-hexose. Some evidence regarding the configuration of the amino-sugar derivatives is included.

The synthesis and solvolysis of some fully acetylated glycopyranosylulose chlorides

Abstract Several partially acetylated aldopyranosyl chlorides with an unprotected hydroxyl group at C-2 have been synthesised and some have been oxidised with ruthenium tetraoxide. In this way, fully acetylated pyranosylulose chlorides having the α- D - arabino -hexo, α- D - lyxo -hexo, and β- L - erythro -pento structures have been prepared. Their rates of methanolysis have been determined. Key intermediates in the synthetic sequences were the per- O -acetyl-2- O -trichloroacetylglycopyranosyl chlorides, of which the α- and β- D - galacto , α- and β- L - arabino , and α and β- D - xylo compounds were hitherto unknown. The β- D - xylo derivative exists in the conformation in which all the ring substituents are axially disposed, whereas the α- L - arabino compound is a rare example of an acylated pentopyranosyl chloride that adopts, preponderantly, a chair conformation that places the halogen in an equatorial orientation.

Boric acid derivatives as reagents in carbohydrate chemistry : Part IV. The interaction of phenylboronic acid with hexopyranoid compounds☆

Abstract Methyl β- d -glucopyranoside, like the α-anomer, racts smoothly with phenylboronic acid (1 mol) to give a 4,6-cyclic boronate which, with excess of reagent, forms a 2,3-pyroboronate. The nature of the products obtained from hexopyranoid derivatives which possess the d -lyxo-configuration at C-3, C-4 and C-5 was found to be dependent upon the substituents at C-1 and C-2. Whereas methyl α- and β- d -galactopyranoside, methyl 2-deoxy-β- d -lyxo-hexopyranoside, 1,5-anhydro- d -galacitol, and 1,5-anhydro-2-deoxy- d -lyxo-hexitol afforded 4,6-cyclic esters in good yield, the only products obtained from d -galactal and methyl 2-deoxy-α- d -lyxo-hexopyranoside possessed the 3,4-cyclic structures.

Further studies of ruthenium tetroxide as an oxidant for carbohydrate derivatives

Abstract An extension is reported of the evaluation of ruthenium tetroxide as an oxidant for the conversion of partially protected carbohydrates into glycosulose derivatives. It has been demonstrated that free hydroxyl groups in benzoic and toluene- p -sulphonic esters, and in N -acetamido derivatives of glycosides can all be oxidised successfully by the reagent. It has been shown also that the oxidant converts 1,4:3,6-dianhydrohexitols into the corresponding 2,5-dione; no significant selectivity in the oxidation of endo and exo hydroxyl groups was noted. Comment is made on the abnormally high optical rotation of the bis(2,4-dinitrophenylhydrazone) of 1,4:3,6-dianhydro- d - threo -hexo-2,5-diulose.

Branched-chain sugars : Part XII. Branched-chain sugars derived from methyl 2,3-O-isopropylidene-β-l-erythro-pentopyranosid-4-ulose, and a synthesis of l-apiose

Abstract The preparation of methyl 2,3- O -isopropylidene-β- l - erythro -pentopyranosid-4-ulose and the conversion of this compound into branched-chain sugar derivatives are described. Reactions at the carbonyl group in the pentopyranosid-4-ulose have been found to give, preferentially, products having the l - ribo configuration. A route to l -apiose is outlined.

Studies with radioactive sugars : Part III. The mechanism of the anomerisation of ethyl α- and ⨿-D-xylopyranoside☆

Abstract Parallel anomerisations of the ethyl D -xylopyranosides in radioactive ethanol and of the radioactive glycosides in unlabelled ethanol have allowed the conclusion to be drawn that the reactions proceed largely by way of a cyclic, ionic mechanism. In principle, these procedures permit a quantitative assessment of the relative significance of this mechanism and a process involving an acyclic ion. The displacement reactions at C-1 occurs predominantly with inversion of configuration, but, particularly with the β- D anomer, significant proportions of isomers having retained anomeric configuration are initially formed.

Aspects of the p.m.r. spectra of branched-chain methyl glycopyranosides

Abstract The chemical shifts and proton coupling constants of various methyl O-isopropylideneglycopyranosides have been measured. It has been shown that the variation in the chemical shift of the endo-methyl group of the isopropylidene residue provides a convenient method for the determination of the configuration of branched-chain glycopyranosides.

Studies with radioactive sugars : Part II. The ethanethiolysis of d-xylose

Abstract d -Xylose in ethanethiol- N,N -dimethylformamide (4:1), and in the presence of an acid catalyst, reacts to give ethyl thiofuranosides which are then converted chiefly into d -xylose diethyl dithioacetal. This then slowly loses water and unergoes migration of an ethylthio group to give 3-ethylthio-2-(ethylthiomethyl)furan. Pyranosides do not comprise more than 6% of the products of ethanethiolysis at any stage.

Branched-chain sugars : Part XI. A synthesis of 6-deoxy-4-C-vinyl-l-talose and 5-deoxy-3-C-vinyl-l-lyxose

Abstract The preparation is described of the title compounds as intermediates in a projected synthesis of streptose. Treatment of methyl 6-deoxy-2,3- O -isopropylidene-α- L - lyxo -hexopyranosid-4-ulose with vinylmagnesium bromide gave methyl 6-deoxy-2,3- O -isopropylidene-4- C -vinyl-α- L -talopyranoside from which 6-deoxy-4- C -vinyl- L -talose (5) was obtained by sequential deacetonation and glycoside hydrolysis. Oxidation of 5 with 1 equivalent of lead tetra-acetate gave 5-deoxy-3- C -vinyl- L -lyxose.