Replacement of hydroxyl with

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... 

Since pyridazines are known to undergo electrophilic substitution only with difficulty, direct halogenation is not expected to be a method of wide application. Therefore, bromine in acetic acid is widely used for dehydrogenation of reduced pyridazines. In some instances simultaneous dehydrogenation of the pyridazine nucleus and bromina-tion of the attached aryl radical has been observed. Dehydrogenation and replacement of hydroxyls with bromine atoms occurs if hexahydro-3,6-pyridazinedione is treated with excess POBrg, giving 3,6-dibromopyridazine. ... 

A number of poly (thiol esters) have been synthesized by method BC (29). The reaction temperature was increased from room temperature to above 200°C. The products were often colored because of side reactions (replacement of hydroxyl with chlorine, formation of ketene structures, and ester pyrolysis are known side reactions in polyester formation). 

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)... 

Bu2SnO, benzene BnBr, DMF, heat, 80% yield. This method has also been used to protect selectively the anomeric hydroxyl in a carbohydrate derivative. The replacement of Bu2SnO with Bu2Sn(OMe)2 improves the process procedurally. The use of stannylene acetals for the regioselective manipulation of hydroxyl groups has been reviewed. ... 

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-... 

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-... 

The 3D structure of 11P-HSD-2 shows that NAD+ has stabilizing interactions between the ribose hydroxyl and aspartic acid-91, serine-92, and threonine-112. Replacement of NAD+ with NADP+ reveals a coulombic repulsion between the 2 -phosphate group and aspartic acid-91. However, 11P-HSD type 2 lacks a nearby amino acid with a positively charged side chain that could compensate for the negative charge on aspartic acid-91. This explains the preference of 11 P-HSD-2 for NAD+. 

The selective replacement of hydroxyl groups in carbohydrates by chlorine has been achieved by the use of sulfuryl chloride.1,74,87,88 The reaction of sulfuryl chloride with maltose89,90 and methyl /3-maltoside24 has been studied. Treatment of maltose with sulfuryl chloride, initially for 2 h at — 70° and then processing at room temperature, gave, after methyl glycosidation and dechlorosulfation, a low yield... 

There have been several further examples of the replacement of hydroxyl or oxo substituents with halogens in 1,7-phenanthrolines using phosphorus halides or oxyhalides.96,169-171,215 In 4,10-dioxo-l,4,7,10-tetrahydro-1,7-phenanthroline (100) there are marked differences in the ease with which the two oxo groups are replaced by halogen.171 With 1 mole of phosphorus pentachloride, the product is 4-chloro-10-hydroxy -... 

Several further examples have been reported of the replacement of hydroxyl (or oxo) substituents in 1,10-phenanthrolines by halogens with phosphorus halide reagents.38 96 196,198,213 213,219,293,340-342 4-Ethoxy-7-hydroxy-l,10-phenanthroline reacts normally with diazomethane to afford 4-ethoxy-7-methoxy-1,10-phenanthroline.203... 

A major part of this chapter is concerned with a discussion of a method for the synthesis of chlorodeoxy sugars by direct replacement of hydroxyl groups by chlorim... 

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