Dialdoses chain extension

A related reaction of more general applicability occurs with the octos-3,7-diulose derivative 27, which was made from the C-3 epimer of dialdose acetal 4 by treatment with (2-oxopropylidene)triphenylphosphorane in a Wittig chain extension reaction, followed by hydrogenation of the resulting enone and oxidation of the alcohol groups at C-3 and C-7. Cyclilzation to give the crystalline tertiary alcohol 28 in 81% yield is promoted by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in refluxing benzene (Scheme 7) [16]. 

Methods for the chemical synthesis of glycuronic acids include (i) reduction of the monolactones of aldaric acids, (ii) oxidation of the primary alcoholic group of aldose derivatives, (iii) oxidative degradation procedures, (iv) chain-extension reactions on dialdoses, and (v) epimerization reactions. 

An important transformation of dialdoses is the chain extension to homologous products by condensations performed on the aldehyde group. When asymmetric induction occurs, this transformation is extremely valuable for the stereocontrolled synthesis of higher sugars. 

Other alternatives for chain extension have been developed. Wittig condensation between the dialdose derivative 194 and the (PPI13I) monosaccharide derivative 195 occurs with complete stereoselectivity, forming a cis linkage. Compound 196 is the precursor of a deaminotunicamine derivative.399... 

Three papers describing chain-extensions by use of C-6-aldehydes have been published the diacetonegalactose-derived dialdose 31 was extended by two carbons to give the acetamido-dideoxy-octosulose derivative 33 via intermediate 32 by consecutive treatment with potassium cyanide in the presence of ammonia,... 

Chain-extension of aldoses or dialdoses with ethyl diazopyruvate furnished sugar 2,4-diketoesters, such as compounds (29) and (30), respectively, suitable for transformation into complex carbohydrates containing heterocyclic moieties, and Pd-catalysed trimethylene cycloaddition (see Trost et ai, J. Am. Chem. Soc., 1991,113, 9007) of diacetone D-galacto-... 

Chain Extension. - Aldolase-catalysed aldol condensation reactions used in the synthesis of sialic acids and aza-sugars have been reviewed (38 refs.). Addition of 2-thiazolyl reagents to the nitrone 2, available from the D-galacto-dialdose 1, featured in syntheses of destomic acid 3 and... 

Several compounds of this type, formally derived from aldoses by oxidation of the terminal CH2OH group to -CHO, have been prepared. Dialdoses arise as intermediates in structural studies, but they are also valuable starting materials for synthetic conversions, in particular for natural-product synthesis. A branched-chain dialdose, streptose (167), occurs as a component of the antibiotic streptomycin. The structure of streptose was elucidated after extensive investigations of its derivatives and transformation products.371 The 2,5-dimethoxytetrahydrofuran fulvanol (168), an analogue of apiose, has been isolated from the plant Hemerocallis fulva 12... 

The utility of this approach to long-chain sugars (thiazole route to carbohydrates) is illustrated by the conversion of protected L-threose (5) and dialdogalactopjranose (6) into higher homologs (eqs 9 and 10).The extension of this methodology to other dialdoses has been reported. ... 

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