Hydroxamic acids reaction with phenolic

Direct amidation can be carried out if an aromatic compound is heated with a hydroxamic acid (34) in polyphosphoric acid, but the scope is essentially limited to phenolic ethers.The reaction of an aromatic compound with aniline, BU4NF and KMn04 led to the diarylamine. The formation of hydroindole derivatives was accomplished by reaction of a A-carbamoyl phenylethylamine derivative with phenyliodine (III) diacetate, followed by Bu4NF. Direct amidation via ipso substitution by nitrogen was accomplished when a A -methoxy arylethylamide (35) was... 

In the synthesis of hydroxamic acid 19a, having a free quaternary amino group (see Scheme 4.4), the intermediate sulfone 21 was synthesized by Pd-catalyzed reaction of phenol with p-bromo derivative 20 [24], Lithiation of 20, followed by nucleophilic addition to the A-Cbz imine of trifluoropyruvate 22 [25] afforded the a-CF3 a-amino acid derivative 23 in fair yields. Basic hydrolysis of the ester function gave the carboxylic acid 24, which was submitted to condensation with ()-15 n-hydroxylamine, affording hydroxamate 25. The subsequent hydrogenolysis of 25 afforded the target molecule 19a. 

Carboxylic acids can be attached to these linkers using methods of ester bond formation such as carbodiimide/DMAP [23] and acid chloride/base. For the loading of N-protected-a-amino acids in particular, an array of different methods has been developed to minimize enantiomerizahon and dipeptide formation during the esterification reaction. These include the use of MSNT/N-methylimidazole [24], mixed anhydrides generated with 2,6-dichlorobenzoyl chloride [25], esters of 2,5-diphenyl-2,3-dihydro-3-oxo-4-hydroxythiophene [26] and acid fluorides [27]. Phenols and N-protected hydroxylamines have been immobilized using the Mitsunobu reaction [28, 29], The latter are particularly useful for the preparation of hydroxamates [29, 30],... 

In these reactions the tested organic substance and an inorganic salt give a more or less stable strong color due to a complex salt. In Part 2 of this monograph a series of such reactions is described, such as, for example, the reaction of hydroxamic acids with ferric salts (p. 276), the reaction of phenols with ferric chloride (p. 188), the reaction of molybdenum with o-dihydro-xybenzenes (p. 191), of diacetyl dioxime with nickel salts (p. 227), of phenols with Millon s reagent (p. 196), alcohols with ceric ammonium nitrate (p. 170), alcohols with vanadium-hydroxy quinoline complex (p. 171), and the reaction of cis-enols of )5-dicarbonylic compounds and a-dicarbonyl compounds with ferric chloride, (p. 294.)... 

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