Hydroxamic acids reaction with aromatic compounds

The hydroxamic acid function in most alicyclic and aromatic compounds is stable to hot dilute acid or alkali, and derivatives cannot undergo normal base-catalyzed Lessen rearrangement. Di Maio and Tardella," however, have shown that some alicyclic hydroxamic acids when treated with polyphosphoric acid (PPA) at 176°-195° undergo loss of CO, CO.2, or H2O, in a series of reactions which must involve earlj fission of the N—0 bond, presumably in a phosphoryl-ated intermediate. Thus, l-hydroxy-2- piperidone(108) gave carbon monoxide, 1-pyrroline (119), and the lactams (120 and 121). The saturated lactam is believed to be derived from disproportionation of the unsaturated lactam. 

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... 

Substitutions and Displacements [1,904J Direct amidation of aromatic compounds can sometimes be achieved by reaction with a hydroxamic acid in PPA 48a... 

A positive reaction is obtained, however, with a series of nonphenolic compounds aromatic amines, ends or hydroxymethylene compounds, tautomeric jS-diketones, j -ketoesters, derivatives of malonic acid esters or of cyanoacetate with a negative substituent at the -- CH2 group, some isonitrites, hydroxylamine derivatives, oximes, hydroxamic acids, and certain derivatives of sulfur. 

Corbett, M. D. 1974. Hydroxamic acids from the reaction of active acetaldehyde with aromatic nitroso compounds. Bioorg. Chem. 3 361-365. 

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