Ulose

Ketoses are characterized by the ending ulose m their name Most nat urally occurring ketoses have their carbonyl group located at C 2 Like aldoses ketoses cyclize to hemiacetals and exist as furanose or pyranose forms... 

Of particular value, was the reagent s ability to oxidize a hydroxyl group attached directly to a furanoid ring (6, 7, 46), as is illustrated by the conversion of l,2 5,6-di-0-isopropylidene-a-D-glucofuranose into l,2 5,6-di-0-isopropylidene-a-D-n o-hexofuranos-3-ulose (1). The follow-... 

Fortunately, the oxidation of l,2 5,6-di-0-isopropylidene-a-D-glucofura-nose to l,2 5,6-di-0-isopropylidene-a-D-nfoo-hexofuranos-3-ulose (1) can be accomplished using either phosphorus pentoxide (10, 44) or acetic anhydride (10, 52) in methyl sulfoxide although this oxidation is effected with ruthenium tetroxide (6,7, 46), it is exceeding difficult with other oxidizing agents (53). Keto-sugar 1 is reduced stereospecifically... 

Rearrangement of methyl 4,6-0-benzylidene-3-deoxy-3-phenylazo-aldohexopyranosides with alkali provides a new route to hexosid-3-uloses (18). 

Derivatives of 6-deoxy-hex-5-enopyranosides are important intermediates in the synthesis of dicarbonyl sugars, namely hexos-5-uloses. For... 

By monitoring the intensity of the carbonyl absorption it was observed that oxidation of methyl 4,6-0-benzylidene-2-deoxy-a-D-Zt/ ro-hexopyrano-side with chromium trioxide-pyridine at room temperature gave initially the hexopyranosid-3-ulose (2) in low concentration, but attempts to increase this yield resulted in elimination of methanol to give compound 3. However, when methyl 4,6-0-benzylidene-2-deoxy-a-D-Zt/ ro-hexo-pyranoside is oxidized by ruthenium tetroxide in either carbon tetrachloride or methylene dichloride it affords compound 2 without concomitant elimination. When compound 2 was heated for 30 minutes in pyridine which was 0.1 M in either perchloric acid or hydrochloric acid it afforded compound 3, but in pyridine alone it was recoverable unchanged (2). Another example of this type of elimination, leading to the introduction of unsaturation into a glycopyranoid ring, was observed... 

From the reaction of 5-0-benzoyl-l,2-0-isopropylidene-o -D-en/t/iro-pentofuranos-3-ulose (prepared in 80% yield by oxidation of 5-0-benzoyl-l,2-0-isopropylidene- -D-xylofuranose (35,36) with ruthenium tetroxide) with an excess of diazomethane in methanol-ether, two main products (m.p. 44°-45°C. and 76°-77°C.), both epoxides, could be isolated by chromatography of the product on a silica column. An... 

Diastereoselective amino nitrile formation from the following ulose may, however, be attributed to thermodynamic control. Flash chromatography of the product provides only one ri bo-derivative28. 

Note. For simple aldoses up to aldohexoses, and ketoses up to hept-2-uloses, the anomeric reference atom and the configurational atom are the same. 

The trivial names D-erythrulose for D-g/ycero-tetrulose, D-ribulose for D-eryf/iro-pent-2-ulose, and D-xylulose for D-fhreo-pent-2-ulose contain stereochemical redundancy and should not be used for naming derivatives. Sedoheptulose is the accepted trivial name for D-a/rro-hept-2-uIose. 

The stem names are formed from the corresponding aldose stem names (2-Carb-8.2) by replacing the ending -ose with -ulose , preceded by the locant of the carbonyl group, e.g. hex-3-ulose. The chain is numbered so that the carbonyl group receives the lowest possible locant. If the carbonyl group is in the middle of a chain with an odd number of carbon atoms, a choice between alternative names is made according to 2-Carb-2.2.2. 

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