Cyclic hydroxamic acids of the indole series

A convenient method was developed for obtaining 2-N-hydroxy-3-keto-1-phenyl-1,3-dihydropyrrolo[3,4-b]indoles by reaction of indole-2-hydroxamic acid with substituted benzaldehydes. Complex compounds of trivalent iron salts with cyclic hydroxamic acids were isolated.Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 227–229, February, 1985.     

Photochemistry of hydroxamic acids

Photochemical reactions of hydroxamic acids have been studied. The intermediacy of a RCONH radical is postulated, based on oxidations achieved with DCA under photochemical conditions.     

Non-aqueous titration of hydroxamic acids

Benzohydroxamic acid is titrated with 0.1M tetrabutyl-anunonium hydroxide in nine non-aqueous solvents with three different indicating electrodes. The best results are obtained using dimethylformamide as solvent and platinum-platinum electrodes. Four monoprotic and three diprotic hydroxamie acids and iron(III) benzohydroxamate have been successfully titrated with this system. The effect of quantitative additions of carbon dioxide to the titrant on its apparent molarity are found to be dependent on the amount added, the strength and sample size of acid titrated and the solvent used.     

First O-glycosylation of hydroxamic acids

The first O-glycosylation of hydroxamic acids is reported. This process involves the use of glycosyl N-phenyl trifluoroacetimidates as glycosyl donors in the presence TMSOTf and 4 A molecular sieves in dichloromethane. Under such conditions, a wide range of new glycosyl donors including glucosyl, galactosyl, mannosyl, glucuronyl, and ribosyl hydroxamates were prepared in good to high yields. This procedure appears to be an advantageous alternative for the synthesis of glycosyl hydroxamates of biological interest.     

Cyclic glycol ethers derived from dialkylstannanediols

The splitting of polydialkylstannoxanes (R₂SnO)(inm) is studied by 1,2-, 1,3-, 1,4-, 1,5-, and 1,6-glycols. In this way ten glycol ethers of dialkylstannanediols, mainly with 5,6, or 10-membered rings, are obtained, eight of which were previously unknown.     

Improved solution- and solid-phase preparation of hydroxamic acids from esters

The addition of small amounts of solid KCN to solution and solid-phase esters in THF/MeOH/50% aqueous NH2OH increases the efficiency of their transformation to the corresponding hydroxamic acids.     

Acidity of hydroxamic acids and amides

The relatively strong acidity of hydroxamic acids was analyzed by means of isodesmic reactions in which this acid or its anion is formed from simpler precursors. Acidity of amides was analyzed in the same way. Energies of all compounds involved in the reactions were calculated at the B3LYP/AUG-cc-pVTZ//B3LYP/6-311 + G(d,p) level; at this level a good agreement was reached with the sparse experimental data. Interpretation of the results was the same as in the recent discussion of the acidity of carboxylic acids, and the conclusions were similar: both amides and hydroxamic acids are stabilized with respect to simpler reference molecules of amines or N-alkylhydroxylamines, respectively. However, their anions are stabilized still more and are responsible for the acidity. This effect is stronger in hydroxamic acids or amides than in carboxylic acids. The problem of whether it is due to resonance depends on the definition of this term. Semiquantitative comparison suggests that resonance in hydroxamic acids is more important than in amides and still more than in carboxylic acids. The stronger acidity of hydroxamic acids compared to amides is due to the destabilizing inductive effect of the hydroxyl group in the acid molecule, not to any effect in the anion.     

Conformational behavior of some hydroxamic acids

The conformational preferences of a few hydroxamic acids are investigated by the density functional B3LYP/6-311++G**//B3LYP16-31G* and semiempirical AM1 and PM3 methods in this work. It is found that both semiempirical methods give satisfactory results in comparison with sophisticated DFT and ab initio calculations, except for the activation barriers, which are overestimated. Of the two semiempirical methods, while the PM3 method gives better results for relative stabilities, AM1 geometries are in slightly better agreement with the experiments. The keto forms are found to be most stable and the reaction pathways for the interconversion between the keto and enol forms have been deduced. The effect of solvation on the reaction has also been investigated, as has the effect of methyl substitution at the carbon and nitrogen atoms. All the investigated acids exhibit N-acid behavior.     

Arylhydroxyacetic acids and amino acids derived from ethinylphenols

Conclusions A method of synthesis of arylhydroxyacetic acids and ammo acids derived from ethinylphenols has been developed in view of possible physiological activity of these compounds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1170–1172, May, 1970.     

Oxoarylation of ynamides with N-aryl hydroxamic acids

Ynamides are electron-rich alkynes with unique reactivities and act as flexible building blocks in organic synthesis. Therefore, the investigation for transformation of ynamides with exceptional selectivity and efficiency is attractive and interesting. Herein, we report an oxoarylation of ynamides with N-aryl hydroxamic acids. In the presence of catalytic Cu(OTf)₂, both the terminal and internal ynamides could undergo an addition/[3,3] sigmatropic rearrangement cascade with N-aryl hydroxamic acids to achieve oxoarylation, along with providing selective entry to (ortho-amino)arylacetamides and oxindoles. Moreover, deuterium-labelling reaction and gram-scale reaction were conducted to probe the mechanism and showcase the scalability.     

Solvent extraction of metals with hydroxamic acids

Solvent extraction with hydroxamic acids has been investigated. with comparison of aliphatic and aromatic reagents for the extraction of iron, copper, cobalt and nickel. Caprylohydroxamic acid has been evaluated for use in extraction systems for titanium, vanadium, chromium, molybdenum and uranium, both in terms of acidity of aqueous phase and oxidation state of the metal. It has been established that caprylohydroxamic acid in 1-hexanol is a suitable extractant for the removal of titanium(IV), vanadium(V), chromium(VI), molybdenum(VI) and uranium(VI) from 6M hydrochloric acid.     

Metal-free oxyaminations of alkenes using hydroxamic acids

A radical-mediated approach to metal-free alkene oxyamination is described. This method capitalizes on the unique reactivity of the amidoxyl radical in alkene additions to furnish a general difunctionalization using simple diisopropyl azodicarboxylate (DIAD) as a radical trap. This protocol capitalizes on the intramolecular nature of the process, providing single regioisomers in all cases. Difunctionalizations of cyclic alkenes provide trans oxyamination products inaccessible using current methods with high levels of stereoselectivity, complementing cis-selective oxyamination processes.     

Hydrogen bond cooperativity in dimers of hydroxamic acids

Molecular orbital calculations are performed on various dimeric forms of four tautomers each of thioformohydroxamic acid and formohydroxamic acid. The analysis of stabilization energies associated with the dimerization and their correlation to proton affinities and deprotonation enthalpies of different potential sites present in the molecules indicate that the highest stabilization results when the most basic, site of the molecule acts as hydrogen bond acceptor but combination of the most acidic and the most basic site does not result in the largest stabilization when dimerization occurs. The presence of hydrogen bond cooperativity is indicated and the reasons for the observed cooperativity are explored in this study. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011