Furanose derivatives, additive

While the above studies were in progress results from dioxane derivatives were published (19,94) which support all of the comments and cautions we have made above. Additional reports have been made of a long-range coupling across a ring oxygen in an unsaturated pentopy-ranose derivative (17) and in a saturated furanose derivative (20). 

The review by Neely tabulated the characteristic frequencies of several common, substituent groups that are of interest in carbohydrate chemistry, and discussed in detail the results of the structural analysis - of pyranose derivatives in the region 730-960 cm.-. In addition, brief outlines were also given of a similar analysis (see Ref. 69) of furanose derivatives (less fruitful than that of pyranose derivatives) and of the investigations of variation in hydrogen bonding in celluloses. 

Aldoses incorporate two functional groups C=0 and OH which are capable of react mg with each other We saw m Section 17 8 that nucleophilic addition of an alcohol function to a carbonyl group gives a hemiacetal When the hydroxyl and carbonyl groups are part of the same molecule a cyclic hemiacetal results as illustrated m Figure 25 3 Cyclic hemiacetal formation is most common when the ring that results is five or SIX membered Five membered cyclic hemiacetals of carbohydrates are called furanose forms SIX membered ones are called pyranose forms The nng carbon that is derived... 

As conformational anomeric effects represent only a fraction (—1 to —3 kcal/mol) of the global enthalpic anomeric effect or gem-dioxy stabilizing effect (—6 to —17 kcal/mol), additional factors have to be taken into account. Depending on substitution, steric factors can affect the relative stability of acetal conformers. Dubois et al.2S have demonstrated that in furanose pyranose derivatives a bulky substituent at the furanose... 

The reactivity of the carbonyl group in a,/3-unsaturated dialdoses was studied in more detail. The interaction with phenylhydrazine and its derivatives led to different results. 3-0-Benzyl-l,2-0-cyclo-hexyl idene-5,6-dideoxy-a-D-xyZo-hept-5-e nodialdo-l,4-furanose (56) gave57 a (2,4-dinitrophenyl)hydrazone. Action of (2,4-dinitrophenyl)-hydrazine on derivatives 67 led18 to complex mixtures. In the case of the acetylated derivatives (66), as well as of branched-chain derivatives (69), the interaction with (2,4-dinitrophenyl)hydrazine resulted in the formation of the expected hydrazones (Refs. 24 and 51, respectively). The interaction with phenylhydrazine was, however, proved to proceed by two paths in this case. Only the nitro derivatives (66, R = p-nitrophenyl) and (69, R = p-nitrophenyl) were shown24,51 to form the expected hydrazones. The phenyl derivative 66 (D-galacto, R = Ph) and p-methoxyphenyl derivative 69 (R = p-MeOC8H4) afforded substituted pyrazolines (74) (Ref. 24) and (75) (Ref. 51), respectively, as a result of subsequent intramolecular addition of a... 

Dehydration Reactions. Detailed analysis of the pyrolysis tar as discussed previously (Figure 12 and Scheme 3) shows the presence of levoglucosan, its furanose isomer (1,6-anhydro-p-D-glucofuranose) and their transglycosylation products as the main components. In addition to these compounds, the pyrolyzate contains minor amounts of a variety of products formed from dehydration of the glucose units. The dehydration products detected include 3-deoxy-o-erythrohexo-sulose, 5-hydroxymethyl-2-furaldehyde, 2-furaldehyde (furfural), other furan derivatives, levoglucosenone (l,6-anhydro-3,4-dideoxy-P-D-glycerohex-3-enopyranos-2-ulose), l,5-anhydro-4-deoxy-D-hex-l-ene-3-ulose, and other pyran derivatives. The dehydration products are important as intermediate compounds in char formation. 

---