Anhydro compounds preparation

Among them, the first compound prepared and studied was 3,5-anhydro-1,2-0-isopropylidene-a-D-xylofuranose (87)347 349 and its 1,2-O-cyclohexy-lidene analogue.350 Formation of the oxetane ring is based on the internal substitution of an conventional leaving group X at C-5, or surprisingly, also phthalimido group in 86 351 for application of the Mitsunobu reaction, see Ref. 349. 

Esters of polyols (polyalcohols) and higher fatty acids frequently are used as non-ionic emulsifying agents. The sorbitan esters of fatty acids eure well known. They are prepared by esterification of sorbitol with fatty acids at temperatures of at least 190°C, usually at 220-240°C. During the reaction, a substantial portion of the sorbitol (more them 75%)is converted into anhydro-compounds (intramolecular ethers like sorbitan and isosorbide). The products become less hydrophilic due to the foirmation of these anhydro-compounds. 

Polyol esters of fatty acids cem be prepeured without simultaneous formation of anhydro-compounds by reesterification of the methyl or glyceryl esters in a polar solvent, in the seime way that sucrose esters have been prepared. Residues of the toxic solvents are difficult to eliminate from the final products,emd this creates problems for the products to be used in foods. 

Trideoxy-2,3,4-trifluoro-D-glucose and -D-galactose derivatives have been prepared. The known 1,6-anhydro compound (13), treated with DAST, gave the product (14) with retention of configuration, whereas the alcohols (15) and (16), on treatment with DAST, gave the products (17) and (18) resulting from... 

Oxirans. - The preparation, and applications in synthesis, of a series of 1,6 2,3- and l,6 3,4-dianhydro-P-D-hexopyranoses has been reviewed. Some isopropylidene derivatives of D-glucose and D-mannose have been converted into 5,6-anhydro-derivatives by treatment with TsCl in the presence of KOH, and other 5,6-anhydro compounds have been prepared via the corresponding 5,6-thionocarbonates, which were opened with methyl iodide to give the 6-deoxy-6-iodo-5-O-methylthiocarbonates followed by treatment with base. ... 

Some 1,2-anhydro-aldofuranose derivatives (e.g. 15) have been prepared by base treatment of 2-O-tosylates. D-Mannose has been converted into the glycosyl chloride 16 from which the 1,2-anhydro derivative 17 was obtained. Similarly, the D-fucosyl chloride 18 was converted to the 1,2-anhydride 19 via the corresponding P-fluoride. Tri-O-acetyl-D-glucal and -galactal have been epox-idized (Scheme 3) to give 1,2-anhydro-compounds 20 and 21 respectively as the major products, and use of a 1,2-anhydro-hexopyranose in the synthesis of an antifungal furanone glycoside is covered in Chapter 3. 

Deoxy-D-jcylo hexose 6-(dihydrogen phosphate) (21) has also been synthesized (2) the reaction sequence makes use of 3-deoxy l 2,5 6-di-O-isopropylidene D-galactofuranose (16), a compound that can be easily prepared from D-glucose (2, 60). The mono-isopropylidene derivative (17) formed by partial hydrolysis of the di-ketal is converted into the 6-tosylate (18) by reaction with one molar equivalent of p-toluenesulfonyl chloride. From this the epoxide (19) is formed by reaction with sodium methoxide. Treatment of the anhydro sugar with an aqueous solution of disodium hydrogen phosphate (26) leads to the 6-phosphate (20)... 

The 4-triflates 277, 279, and 281 of benzyl 2,3-anhydro-o -D- and -) -L-ri-bopyranosides and -a-D-lyxopyranoside gave, - readily, on reaction with BU4NF [CgHg (24 h) or MeCN (5-8 h), r.t.], the respective 2,3-anhydro-4-deoxy-4-fluoro derivatives 278,280, and 282 in good yields. The conformation ( //s) of the starting compounds remained the same after fluorination. Methyl 2,3-anhydro-4-deoxy-4-fluoro-a-L-lyxopyranoside (284, 86%) was prepared from the 4-triflate 283 by treatment with EtjN- 3HF (CH2CI2-EtjN, 40°, 5 h). 

An anhydro sugar which will probably find extensive synthetic use has been described by Hann and Hudson.85 This is the tricyclic compound, 3,4 1,6-dianhydro-jS-D-talopyranose (LXXIV) which is prepared by the saponification of the 4-tosyl derivative of mannosan (LXXIII). 

Starting with the same acetal (35), but proceeding by way of the diacetate 40, instead of the dibenzoate 36, it was possible to prepare,51 in high yield, the p-toluenesulfonate 41 by sequential trityla-tion and p-toluenesulfonylation. Compound 41 was then subjected to solvolysis in the presence of sodium acetate in moist N,N-dimethyl-formamide, and the product (42) was successively acetylated and de-tritylated to give 3,4,6-tri-0-acetyl-2,5-anhydro-D-allitol (43). The... 

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