A.B. Foster

Aspects of stereochemistry—I : Properties and reactions of some diols

Abstract The extent of intramolecular hydrogen-bonding, as determined by infra-red spectroscopy in the hydroxyl stretching region, in certain vicinal diols of cyclo hexane, cyclo pentane, tetrahydropyran and tetrahydrofuran and in related compounds provides evidence for the stabilities of different conformations. In certain compounds these stabilities can be affected by hydrogen bonding from a substituent hydroxyl group to a ring oxygen. Additional evidence is provided in the case of the tetrahydropyran diols by [ M ] D values. The rate of reaction of the vicinal diols of these cyclic systems with glycol splitting reagents, and their zone electrophoretic mobility in an alkaline borate buffer is influenced by the presence of a ring oxygen.

Fluorinated carbohydrates : Part I. 3-deoxy-3-fluoro-d-glucose1

Abstract Treatment of 1,2:5,6-di- O -isopropylidene-3- O -toluene- p -sulphonyl-α- d -allofuranose with tetrabutylammonium fluoride in acetonitrile gave 3-deoxy-3-fluoro-1,2:5,6-di- O -isopropylidene-α- d -glucofuranose ( 6 ) in 74% yield. The structure of 6 was established by a multistage conversion into known 3-deoxy-3-fluoro- d -xylose. Graded hydrolysis of 6 with acid gave 3-deoxy-3-fluoro-1,2- O -isopropylidene-α- d -glucofuranose ( 7 ), and total hydrolysis gave 3-deoxy-3-fluoro- d -glucose (15–18% overall yield from d -glucose). 3-Deoxy-3-fluoro- d -glucose gave a crystalline β-tetra-acetate and was reconverted into 7 on treatment with acetone in the presence of acid, followed by graded hydrolysis with acid. In a similar manner, 1,2- O -cyclohexylidene-3-deoxy-3-fluoro-α- d -glucofuranose was obtained.

Aspects of stereochemistry—II : Intramolecular hydrogen bonding in some monohydroxy derivatives of tetrahydrofuran, tetrahydropyran and 1:3-dioxan

Abstract The extent of intramolecular hydrogen bonding between hydroxyl groups and ring oxygens, as determined by infra-red spectroscopy in the hydroxyl stretching region, in a series of monohydroxy derivatives of tetrahydropyran, tetrahydrofuran and 1:3-dioxan provides direct experimental evidence for the stabilities of different conformations of certain of the alcohols. The synthesis of tetrahydropyran-3-ol is described and the mechanism of the reaction of perbenzoic acid with glycals is discussed.

Observations on esterification reactions

Abstract The rate constants for the esterification of a series of alcohols with acetic anhydride at 25° have been determined. No rate-enhancement effect attributable to intramolecular hydrogen-bonding was observed, in contrast to esterifications with acid chlorides and sulphonyl chlorides in pyridine. With acetic anhydride in pyridine, 1,4:3,6-dianhydro- D -glucitol is selectively acetylated at position 2. If pyridine hydrochloride is also present in the mixture, selective esterification occurs at position 5. The mechanisms of these and related reactions is considered. cis -5-Amino-2-phenyl-1,3-dioxan is more rapidly esterified with acetic anhydride in pyridine than is the trans -isomer; parallel results have been observed in the cyclohexane series.

Intramolecular hydrogen bonding in some acyclic alcohols

Abstract The extent of intramolecular hydrogen bonding, occurring in dilute CCl 4 solutions, of members of the series (n = 2–5) HO.(CH 2 ) n .OH and MeO.(CH 2 ) n .OH has been determined. The results permit the interpretation of the patterns of hydrogen bonding in the three monomethyl ethers of butane-1,2,4-triol and in 1,4-dimethoxybutan-2-ol. In these compounds, where hydrogen bonding allows the formation of rings of different sizes the sequence of preference 5 > 6 > 7 was observed.

The addition of dichloromethylene to unsaturated sugars

Abstract Addition of dichloromethylene to 3,4,6-tri- O -methyl- d -glucal gave a single product that was tentatively identified, by stereochemical considerations as, 1,5-anhydro-2-deoxy-1,2- C -(dichloromethylene)-3,4,6-tri- O -methyl- d - glycero - d - ido -heptitol(1), and was characterised, after demethylation, as the tribenzoate 3 . 3-Deoxy-1,2:5,6-di- O - isopropylidene-α- d - erythro -hex-3-enofuranose reacted with dichloromethylene to give 3-deoxy-3,4- C -(dichloromethylene)-1,2:5,6-di- O -isopropylidene-α- d -galactofuranose ( 6 ), which was then converted by mild hydrolysis with acid into the 1,2- O -isopropylidene derivative ( 8 ). Reduction of compound 1 and 6 with lithium aluminium hydride gave the corresponding cyclopropyl derivatives, 4 and 7, respectively.

Components of royal jelly : 10-hydroxy-trans-dec-2-enoic acid☆

Abstract Chemical and physical evidence is cited which proves that the olefinic linkage in 10-hydroxydec-2-enoic acid, isolated from royal jelly, has the trans-configuration.

Further observations on the acid-catalysed benzaldehyde-glycerol reaction

Abstract The proportions of cis - and trans -5-hydroxy-2-phenyl-1,3-dioxan and cis - and trans -4-hydroxymethyl-2-phenyl-1,3-dioxolan in acid-catalysed, equilibrated, O -benzylidene-glycerol mixtures are critically dependent on solvent and temperature. In carbon tetrachloride, elevation of temperature increases the proportion of dioxolan derivatives and, at a given temperature, diminishing concentration increases the proportion of the cis -1,3-acetal at the expense of the trans -isomer. At equilibrium in dimethyl sulphoxide, the trans -1,3-acetal is preponderant. On acid-catalysed benzylidenation of glycerol under homogeneous conditions ( N , N -dimethylformamide), the 1,2-acetals form rapidly in the initial, kinetic phase, and the 1,3-acetals are preponderant at equilibrium. A rationalisation of some of these observations is presented.

Derivatives of 2-hydroxy-1,4-oxathiane and 2-hydroxymorpholine. A new class of sugar☆

Abstract Application in sequence of periodate oxidation, borohydride reduction, tosylation, and treatment with sodium sulphide to methyl α- l -rhamnopyranoside affords (2 R ,6 S )-2-methoxy-6-methyl-1,4-oxathiane. Likewise, methyl 6- O -trityl-α- d -glucopyranoside and 1,6-anhydro-β- d -glucopyranose were converted into 1,4-oxathiane derivatives. Acid-catalysed equilibration of (2 R ,6 S )-2-methoxy- and (2 R ,6 S )-2-acetoxy-6-methyl-1,4-oxathiane affords, in each case and in contrast to structurally related tetrahydropyran derivatives, a mixture containing ca. 70% of the cis (diequatorial) isomer. Replacement of sodium sulphide by methanolic ammonia in the above reaction sequence results in the conversion of the rhamnoside into (2 R ,6 S )-2-methoxy-6-methylmorpholine. The behaviour of the free amine and the N -acetyl derivative on acid hydrolysis is described. At low temperature, the n.m.r. spectrum of the N -acetyl derivative is consistent with the existence of geometrical isomers.

Mode of decomposition of chloro- and fluoro-formates of some carbohydrates and related compounds

Abstract It has been established that thermal and catalytic decomposition of certain alkyl haloformates affords dialkyl carbonates in addition to alkyl halides. Pyridine(or quinoline)-catalysed decomposition of ethyl and cyclohexyl chloroformate and ethyl fluoroformate affords high yields of alkyl halides, but cyclohexyl fluoroformate yields a significant proportion of dialkyl carbonate. In compounds containing the structural unit O·C-C·O·CO·Hal, chloroformates yield alkyl chlorides and dialkyl carbonates, whereas with fluoroformates, dialkyl carbonates are the sole products. The halo-formates of the following compounds have been examined: cyclohexanemethanol, 2-(hydroxymethyl)tetrahydropyran, 1,2:3,4-di- O -isopropylidene-α- D -galactose, 1,2:3,4-di- O -isopropylidene- DL 0xylitol, and trans -2-methoxycyclohexanol. Quinoline-catalysed decomposition of trans -1,2-bis(fluoroformyloxy)cyclohexane affords mainly the cyclic carbonate of cyclohexane- trans -1,2-diol, together with small proportions of cyclohexa-1,3-diene and an unidentified, volatile product.