Aldehyde sugar

Pressured cycloaddition of (E)-l-methoxybutadiene (18b) with l 2,3 4-di-0-isopropylidene-a-D-galactopyranos-6-ulose (73) diastereoisomerically afforded pure cycloadduct 74, that exhibits the cis arrangement of the methoxy group with respect to the sugar moiety [27] (Scheme 5.7). Similar results were obtained with the sugar aldehydes 75 and 76. 

Ring-chain tautomerism occurs in sugars (aldehyde vs. the pyranose or ftira-nose structures). In benzamide carboxaldehyde (125), whose ring-chain tautomer is... 

Scheme 2. Double N-alkylation of a sugar aldehyde by reductive animation.65...

Fig. 11. Sugar aldehydes condensed directly on pyrrole derivatives by Lindsey s chemistry.

Table 4 Conversion of anomeric sugar aldehydes to oximes 302 and furoxans 304...

Scheme 25 C-Pyranosyl compounds by reaction of the sugar-aldehyde intermediates equilibrating with the pyranoses.

Nitroaldol (Henry) reaction of nitro alkanes with sugar aldehydes... 

The Henry reaction of nitro sugars and sugar aldehydes is a powerful tool for the formation of C-glycosydic bonds. A recent example is the preparation of disaccharide precursor 60 stated in Scheme 21.45 It involves a Henry reaction of nitro sugar 58 and aldehyde 59 in acetonitrile in the presence of catalytic potassium fluoride, to give nitro alcohol 60, a precursor of the corresponding C-disaccharide. 

For example, the 0,C-trisaccharide 153 was obtained by a Henry reaction of nitro disaccharide 151 and sugar aldehyde 150 followed by the dehydration of (3-nitro alcohol 152 and reduction of the resulting nitroolefin, to give nitro sugar 153. Finally, a radical elimination of the nitro group afforded the target 154 (Scheme 47).105... 

Another stereoselective synthesis (Scheme 11) is based on sugar aldehyde 35 and intermediate 36 subsequent 1,2-O-isopropylidine deprotection, N,0-debenzylation/olefin reduction/reductive cyclization in a single pot, and O-acetylation result in the formation of bicyclic aza sugar 37 (09TA1217). 

Catalyst deactivation often plays a central role in manufacturing of various alimentary products. Sugar alcohols, such as xylitol, sorbitol and lactitol, are industrially most commonly prepared by catalytic hydrogenation of corresponding sugar aldehydes over sponge nickel and ruthenium on carbon catalysts (5-10). However, catalyst deactivation may be severe under non-optimized process conditions. 

FEHI.ING S SOLUTION. A reagent used as a test for sugars, aldehydes, etc. It consists of two solutions, copper sulfate and alkaline lartraie. which are mixed just before use. Benedict s modification is a one-solution preparation. 

Z. Pakulski and A. Zamojski, The reaction of acetyliron ((i 5-C5H5)Fe(CO)(PPh3) (COCH3)) with sugar aldehydes. New synthesis of deoxysugars, Tetrahedron, 51 (1995) 871-908. 

B. Grzcszczyk, K. Dziewiszek, S. Jarosz, and A. Zamojski, Asymmetric induction in acid-catalysed condensations of sugar aldehydes with furan and 2-methylfuran, Carbohydr. Res., 145 (1985) 145-151. 

J. M. Lassaletta, R. Fernandez, E. Martin-Zamora, and C. Pareja, Stereospecific addition of formaldehyde dialkylhydrazones to sugar aldehydes. Synthesis of cyanohydrins and a-hydroxy aldehydes, Tetrahedron Lett., 37 (1996) 5787-5790. 

The three-component reaction of indole (2) with sugar hydroxyaldehyde 281 and Meldrum s acid 282, with a catalytic amount of D,L-proline, afforded the 3-substitution product 283 as a single isomer [203]. The substituent possesses the czs-fused furo [ 3,2- b ] pyranonc skeleton. The proline catalyzes the Knoevenagel condensation of the sugar aldehyde 281 and Meldrum s acid 282 to provide the alkylidene derivative 284 of Meldrum s acid. Then a diastereo-selective Michael addition of indole and an intramolecular cyclization of this adduct 285 with evolution of carbon dioxide and elimination of acetone furnish the furopyranone in one-pot (Scheme 62). 

These woikers have also examined asymmetric induction in the process in some detail. For instance, cycloaddition of sugar aldehyde (167) occurred to afford only adduct (169) at high pressure (equation 80). It was suggested that the Diels-Alder reaction proceeds via diene attack on the aldehyde conformation shown in (168) from the least congested face. Other chiral aldehydes have been investigated by this group, as has the e ect of lanthanide catalysts upon the extent of asymmetric induction. Summaries of this work have recently been published. ... 

An interesting approach to azasugars (e. g. 116 in O Scheme 31) from the epoxsides built at the anomeric centers of unprotected carbohydrates was presented recently [78]. Such epoxides (e.g. 115) were obtained with very high selectivity hy reaction of the corresponding hemi-acetals (e. g. 114) with sulfur ylid (O Scheme 31). This reaction is applicable for various sugar aldehydes [79]. 

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