Benzoate protection with

The selectivity here relies on the fact that the j3-benzoate is the thermodynamically more stable ester. A mixture of esters is formed upon hydrolysis of the ortho ester and is then equilibrated with DBU. Carbohydrates are selectively protected with this methodology. " ... 

For the mono-C-glycosylphenol, the commercially available 2,4,6-trihydroxyacetophe-none was chosen and selectively methylated at C-2 and C-4. The partially protected phenol was glycosylated with the C-benzyl-protected glucosyl trichloroacetimidate in the presence of trimethylsilyl triflate as promoter to give directly a C-(benzyl protected)glycosylphenol. The unprotected hydroxyl group of this compound was converted with benzoyl chloride into a fully protected C-glycoside phenol. Treatment of the benzoate derivative with sodium hydroxide in... 

In the first example, nitration of the benzoate (140) with nitric acid affords the nitro derivative. Hydrogenation converts this to the anthranilate (141). In one of the standard conditions for forming quinazolones, that intermediate is then treated with ammonium formate to yield the heterocycle (142). Reaction of 142 with phosphorus oxychloride leads to the corresponding enol chloride (143). Condensation of 143 with m-iodoaniline (144) leads to displacement of chlorine and consequent formation of the aminoquinazoline (145). Reaction with the trimethylsilyl derivative of acetylene in the presence of tetrakis-triphenylphosphine palladium leads to replacement of iodine by the acetylide. Tributylammonium fluoride then removes the silyl protecting group to afford the kinase inhibitor erlotinib (146). ... 

All attempts to convert 40 or its hydroxyl protected derivatives to the enone needed to complete the functionalization of the A-ring were unsuccessful. Most often, treatment of benzoate 50 with a variety of oxidizing agents (e.g., with Collins reagent) led to complex reaction mixtures wherein, in addition to small amounts of the desired enone 51, enone 52 was the major product. 

Other ester-protected PHOST copolymers that have been employed in DUV resist applications include those protected with tert-butoxycarbonylmethyP ° and tert-butyl groups. Poly(4-vinyl benzoate) and poly(methyl methacrylate) are converted to poly(4-vinylbenzoic acid) and poly(methacrylic acid), respectively, by reactions with a photochemicahy generated acid. 

Finally, because benzoic acid is an excellent partner in the Mitsunobu reaction, benzoate formation with inversion has been used to prepare protected variants of relatively rare carbohydrates from readily available precursors. Thus, Mitsunobu esterification at the 3- and 6-positions in methyl (3-D-glucopyranoside proceeded with inversion of the C-3 configuration to provide an efficient synthesis of methyl 3-D-allopyranoside after Zemplen methanolysis (Figure 2.49). The a-anomer was reactive only at the 6-position (to maintain the gluco-configuration) under the same conditions [67]. 

The protected racemic mjo-inositol compound 93 can be alkylated with benzyl bromide or allyl bromide in the presence of silvei(I) oxide to give 94 which are thought to arise due to formation of a comploc which leads to loss of the axial benzoate protecting group. 

The synthesis of Gates and Tschudi (Scheme 13.44) began with 2,6-dihydroxy-naphthalene, which was converted to its monobenzoate and nitrosated. Reduction of the nitroso (H2, Pd/C) yielded the corresponding a-aminophenol, the oxidation of which, with iron(III) chloride, produced a quinone, and reduction of the quinone with sodium hydrosulfite followed by methylation (dimethyl sulfate [(CH3)2S04]) yielded a dimethoxybenzoate. Removal of the benzoate protecting group and repetition of the entire sequence outlined above produced a dimethoxyquinone. 

Methodology. Filippov has reported a one-pot procedure to prepare phosphate, phosphorothioate and phosphorofluoridate monoesters as well as pyrophosphate monoesters of nucleosides. This versatile approach made use of di(p-methoxybenzyl)-A, A -diisopropylphosphoramidite. While little information was provided on the preparation and stability of the phosphoramidite reagent, its use in the reaction with benzoate-protected thymidine in the presence of dicyanoimidazole as an activator yielded the di(p-methoxybenzyl)phosphite of thymidine [46]. This phosphite could subsequently be oxidised (Scheme 3) to the phenylthioate ester [47a], the phosphate monoesters [47b], the phosphoramidate [47c, d], the phosphorofluoridate [47e], the nitrophenolate diester [47f] and to the fully protected dinucleotide [47g]." ... 

BzCl or BZ2O, Pyr, 0°. Benzoyl chloride is the most common reagent for the introduction of the benzoate group. Reaction conditions vaiy depending on the nature of the alcohol to be protected. Cosolvents such as CH2CI2 are often used with pyridine. Benzoylation in a polyhydroxylated system is much more selective than acetylation. A primary alcohol is selectively... 

The benzoate ester is one of the more common esters used to protect alcohols. Benzoates are less readily hydrolyzed than acetates, and the tendency for benzoate migration to adjacent hydroxyls, in contrast to that of acetates, is not nearly as strong, but they can be forced to migrate to a thermodynamically more stable position. The p-methoxybenzoate is even less prone to migrate than the benzoate. Migration from a secondary to a primary alcohol has also been induced with AgN03, KF, Pyr, H2O at 100°. ... 

Soldered brass seldom gives trouble. In radiators, antifreeze solutions have been alleged to cause corrosion, possibly because materials such as ethylene glycol sometimes detach protective deposits. Sodium nitrite, valuable as a corrosion inhibitor for other metals in a radiator, tends to attack solders, but sodium benzoate is safe and, in addition, protects the soldered joint against the action of nitrites. In an investigation of other inhibitors in ethylene glycol solutions, 1% borax, either alone or in combination with 0-1% mercaptobenzothiazole, appeared to be satisfactory. 

Sometimes it is possible to add corrosion inhibitors to an aqueous product that is to remain in contact with tinned steel. The normal inhibitors used for protecting steel, e.g. benzoate, nitrite, chromate, etc. are suitable, provided that they are compatible with the product and that the pH is not raised above 10. In a closed container with an air-space, such inhibitors will not protect the zone above the water-line, and possibly not the water-line zone itself, against condensate. Volatile inhibitors have been used to give protection to these areas. 

Atmospheric corrosion can be prevented by using volatile inhibitors which need not be applied directly to the surfaces to be protected. Most such inhibitors are amine nitrites, benzoates, chromates, etc. They are mainly used with ferrous metals. There is still some disagreement as to the mechanism of action. Clearly, any moisture that condenses must be converted to an inhibitive solution. There is no doubt that the widely used volatile inhibitors are effective in aqueous solutions containing moderate... 

Dissimilar metals in the same system Because of the specific action of many inhibitors towards particular metals, problems arise in systems containing more than one metal. In the majority of cases these problems can be overcome by the choice of a formulation incorporating inhibitors for the protection of each of the metals involved. With this procedure it is necessary not only to maintain an adequate concentration of each of the inhibitors but also to ensure that they are present in the correct proportion. This is because of two effects firstly, failure to inhibit the corrosion of one metal may intensify the attack on the other metal the best example of this is with aluminium and copper in the same system, and failure to inhibit copper corrosion — usually achieved with sodium mercaptobenzothiazole or benzotriazole—can lead to increased corrosion of the aluminium as a result of deposition of copper from copper ions in solution on to the aluminium surface. Secondly, an inhibitor of the corrosion of one metal may actually intensify the corrosion of another metal. Thus, benzoate is usually used to prevent the corrosion of soldered joints by nitrite inhibitor added to protect cast iron in the same system. A benzoate nitrite ratio of greater than 7 1 is necessary in these cases. 

Nature of the metal surface Clean, smooth, metal surfaces usually require a lower concentration of inhibitor for protection than do rough or dirty surfaces. Relative figures for minimum concentrations of benzoate, chromate and nitrite necessary to inhibit the corrosion of mild steel with various types of surface finish have been given in a recent laboratory studyThese results show that benzoate effectiveness is particularly susceptible to surface preparation. It is unwise, therefore, to apply results obtained in laboratory studies with one type of metal surface preparation to other surfaces in practical conditions. The presence of oil, grease or corrosion products on metal surfaces will also affect the concentration of inhibitor required with the... 

Nature of the metal surface The critical concentration of an anion required to inhibit the corrosion of iron may increase with increasing surface roughness. Thus, Brasher and Mercer" showed that the minimum concentration of benzoate required to protect a grit-blasted steel surface was about 100 times greater than that required to protect an abraded surface. However, surface preparation had little effect on the critical inhibitive concentrations for chromate" or nitrite " The time of exposure of the iron surface to air after preparation and before immersion may also affect the ease of inhibition by anions. There is evidence """ that the inhibition by anions occurs more readily as the time of pre-exposure to air increases. Similarly, if an iron specimen is immersed for some time in a protective solution of an inhibitive anion, it may then be transferred without loss of inhibition to a solution of the anion containing much less than the critical inhibitive concentration . ... 

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