Replacement of hydroxyl

An unusual replacement of hydroxyl with the concomitant formation of a 1,2-benzisoxazole occurred with the base treatment of 2,6-dihydroxyacetophenone oxime (554). The use of 0.5 equivalents of KOH/MeOH gave only a 1,2-benzisoxazole. Increasing the concentration of KOH through 2 equivalents gave the 1,2-benzisoxazole and increasing... 

The cellulose molecule is rigid and forms strong hydrogen bonds with adjacent molecules. It is thus insoluble and decomposes before softening on heating. Partial replacement of hydroxyl groups by acetyl groups has a number of effects ... 

Replacement of hydroxyl by fluorine converts perfluoroalkanecarboxylic acids toperfluoroalkanoylfluorides The short chain acids react exothermally with FAR added in a dropwise manner, whereas the longer chain acids require heating [78] (equation 49) Attempts to fluorinate pentafluorobenzoic acid with FAR leads to decarboxylation to give pentafluorobenzene [78]... 

Huonnations with DAST proceed with high chemoselectivity In general, under very mild reaction conditions usually required for the replacement of hydroxyl groups, other functional groups, including phenolic hydroxyl groups [112], remain intact This provides a method for selective conversion of hydroxy esters [95 97] (Table 6), hydroxy ketones [120, 121], hydroxy lactones [722, 123], hydroxy lactams [124] and hydroxy nitriles [725] into fluoro esters, fluoro ketones, fluoro lactones, fluoro lactams, and fluoro nitnles, respectively (equations 60-63)... 

Isopropyl Iodide.—The replacement of hydroxyl by iodine in the action of phosphorus and iodine on alcohols has alieady been described (see Piep. 6, p. 68), but here the presence of an excess of hydriodic acid, which is due to the action of water on the phosphorus iodide,... 

Non-hindered secondary hydroxyl groups have been shown, however, to react under the same conditions giving the corresponding halo derivatives. These direct replacements of hydroxyl groups by halogens are... 

Tr.e cyclic amino acid (25) could be made from a,e-di-cromo acid (26) and this can be made from (27) by a-trominatlon and replacement of hydroxyl by Br. This 1, 6-difunctionalised compound (27) is simply the ring -pened form of lactone (28), the Baeyer-Villiger p T 226) cleavage product from cyclohexanone. 

The selective replacement of hydroxyl groups in carbohydrates by halogen has mainly been achieved by the use of (a) sulfuryl chloride, (b) reagents based on phosphorus compounds, and (c) reagents of the... 

Selective replacement of hydroxyl groups by bromine has been reported for some inositols and inosamines. DL-2-Amino-2-deoxy-epi-inositol hydrochloride plus acetyl bromide in acetic anhydride gave, after 6 hours at 150°, DL-4-acetamido-l,2,6-tri-0-acetyl-3,5-dibromo-3,4,5-trideoxy-c/uro-inositol in 32% yield, the bromine atoms having been introduced with inversion.407 Under related conditions, DL-epi-... 

Replacement of hydroxyl by benzyloxy gives a- and /3-shifts similar to those of methoxyl, and resonances of the 13C-n.m.r. spectrum of methyl 2,3-di-O-benzyl-a-D-galactofuranoside28 have been found to be sufficiently close to those of a polysaccharide containing 2,3-di-O-substituted a-D-galactofuranosyl residues as to make possible a structural confirmation.17... 

Lower members of the series of acid chlorides are colourless liquids the higher members are colourless crystalline solids. At ordinary pressure most of them boil without decomposition. Vacuum distillation is only indicated with those of high molecular weight. The boiling points of the add chlorides are lower than those of the acids, for the replacement of hydroxyl by chlorine usually causes a lowering of the boiling point ... 

Reductive removal of halogen substituents has been of value in the synthesis of pyrimidines and purines since the time of Fisher (1899). Natural purines were de-oxygenated in a sequence of reactions involving the replacement of hydroxyl by chlorine through the reaction with phosphorus pentachloride and the reduction using zinc dust and water [152], 2-Chloropurines 45 are not reduced under these conditions. The 2-iodopurines are however reduced by zinc and water [152]. The elec-... 

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