O-Phenylhydroxylamine

Heating O-phenylhydroxylamine 49 gave 2-aminophenol, though not in very high yield55. A detailed mechanistic investigation of this reaction in trifluoroacetic acid has... 

A synthetic application of this reaction has been reported57 when the rearrangement of 2-aryl-O-phenylhydroxylamines is followed by a ring enlargement to give an aryldihy-droazepinone (Scheme 10). The 2-aryl-2-phenyl intermediate was also trapped out as the N-trifluoroacetamide. 

The only reported example of the use of O-phenylhydroxylamine Ig for electrophilic amination of carbanions is the conversion of phenyhnagnesium bromide into aniline. ... 

NTI (82) and its TV -mcthyl analogue (114) were prepared from naltrexone through a Fischer indole synthesis by treatment with phenylhydrazine and methylphenylhydrazine respectively [170, 187]. NTB (115) was synthesized by reaction of naltrexone with O-phenylhydroxylamine [188],... 

O Phenylhydroxylamines (see also Section I.S) react at room temperature with DMAD to give an enamine which undergoes a Cope rearrangement this cleaves the N—O bond and a pyranone is obtained in high yield. When R = NO2, additional heating of an intermediate with ethanolic hydrochloric acid is necessary. 

By the solvolysis of N-tosyl-O-phenylhydroxylamine, prepared in 75-85% yield from phenoxylamine (Chap. 3) by reaction with 4-toluenesulphonyl chloride in pyridine, 4-fluorophenol resulted regiospecifically in 38% yield accompanied by an imino compound (34%) arising from the reagent which was used at ambient temperature and consisted of a solution of hydrogen fluoride in THF (5 1) (ref. 

Benzofurans and Other Annelated Furans.-A new synthesis of benzofurans (73) is by the reaction of the phosphonium salt (72) with acid chlorides RCOCl in the presence of triethylamine. The benzofuran (74) results from the condensation of hexafluorobenzene with acetylacetone. Three instances of the formation of benzofurans from O-aryl-hydroxylamines, i.e. the oxygen analogue of the Fischer indole synthesis, have been reported O-phenylhydroxylamine hydrochloride and benzenesulphonylacetone give a 2 1 mixture of compounds (73 R = CH2S02Ph) and (75), the oxime ether (76) is converted into the aldehyde (77 ... 

Indolomorphinans can be prepared from their 6-ketomorphinan precursors via Fischer indole synthesis with phenylhydrazine hydrochloride in glacial acetic acid [43, 49, 50], while benzofuromorphinans can be synthesized from the corresponding 6-ketomorphinans using O-phenylhydroxylamine hydrochloride and methanesulfonic acid in MeOH (Scheme 8) [43]. 

A convenient new route " to O-phenylhydroxylamine (134) makes use of the reaction of A(-hydroxyphthalimide (135) with diphenyliodonium chloride to give the novel N-phenoxyphthalimide (136), which on hydrazinolysis gives (134) (Scheme 19). 

Acyl derivatives, RCO—NH—OH and HjN—O—CO—R, are named as A-hydroxy derivatives of amides and as O-acylhydroxylamines, respectively. The former may also be named as hydroxamic acids. Examples are A-hydroxyacetamide for CH3CO—NH—OH and O-acetylhydrox-ylamine for HjN—O—CO—CH3. Further substituents are denoted by prefixes with O- and/or A-locants. For example, C5H5NH—O—C2H5 would be O-ethyl-A-phenylhydroxylamine or A-ethox-ylaniline. 

Additions of silyl-substituted synthons 965 to nitrones such as 962 a in the presence of LDA result in the products 966 which eliminate the lithium salt of O-tri-methylsilyl-N-phenylhydroxylamine 968 to give the olefins 967a or 967b in 72 and 39% yield, respectively [68, 69] (Scheme 7.20). The intermediate lithium salt 968 dimerizes with elimination of LiOSiMe3 98 to form azobenzene and azoxybenzene 961 [68, 69]. 

Heesing and coworkers have reported the rearrangement of 0-alkylsulfinyl-iV-benzoyl-iV-phenylhydroxylamine (143) at — 70°C to the corresponding sulfonamide together with the o- and p-alkylsulfonyl derivatives 144 and 145 (equation 89). The reaction has been suggested to proceed by an intramolecular radical pair mechanism, as evidenced by experiments with oxygen-18 labeling and C-CIDNP effects. 

The transfer of such sequences to various acceptor-substituted allenes 214 and to O-deprotonated N-phenylhydroxylamines 215 was investigated thoroughly by Ble-chert [255, 256]. After the nucleophilic addition forming the intermediate 216, the [3,3]-sigmatropic isomerization takes place at low temperature in only a few minutes... 

O-Substituted phenylhydroxylamines also undergo rearrangement to give the 2-isomers. For example O-(arenesulphonyl) phenylhydroxylamines 47 readily form the 2-sulphonyl derivatives 48. Experiments with 180-labelled compounds led to the suggestion54 of a mechanism involving an ion pair which has only a very short lifetime. 

Pertechnetate in neutral and alkaline media can be extracted into solutions of tetra-alkylammonium iodides in benzene or chloroform. With tetra-n-heptylammo-nium iodide (7.5 x 10 M) in benzene distribution coefficients up to 18 can be obtained . A solution of fV-benzoyl-iV-phenylhydroxylamine (10 M) in chloroform can be used to extract pertechnetate from perchloric acid solution with a distribution coefficient of more than 200, if the concentration of HCIO is higher than 6 M The distribution of TcO between solutions of trilauryl-ammonium nitrate in o-xylene and aqueous solutions of nitrate has been measured. In 1 M (H, Li) NOj and 0.015 M trilaurylammonium nitrate the overall equilibrium constant has been found to be log K = 2.20 at 25 °C. The experiments support an ion exchange reaction . Pertechnetate can also be extracted with rhodamine-B hydrochloride into organic solvents. The extraction coefficient of Tc (VII) between nitrobenzene containing 0.005 %of rhodamine-B hydrochloride and aqueous alcoholic " Tc solution containing 0.0025 % of the hydrochloride, amounts to more than 5x10 at pH 4.7 . 

We now turn to the two aryl hydroxylamines, Af-phenylhydroxylamine and its o-nitro derivative. As liquids, the former compound has an enthalpy of formation that is ca 20 kJmoH more positive than that of the latter. For comparison, we find the enthalpies of the corresponding hquid species without the NHOH group, Le. benzene and nitrobenzene, differ by 36.5 kJmol . Alternatively said, equation 4 is endothermic by 16.1 kJmol . 

The intermediate generated in pyrolysis of IV-acylacetyl-iV-phenylhydroxylamines 48 can form a 3-aza-4-oxa-l,5-diene system (50) (equation 16). A homolytic cleavage of the O—H bond with subsequent rearrangement to the aniline radical, followed by recombination with the hydrogen radical to give the corresponding 0-acyl hydroxylamine 49,... 

Okamoto and co-workers noted that N-phenylhydroxylamine gave predominately diphenylamine on treatment with benzene in TFA but mostly 4-aminobiphenyl and 2-aminobiphenyl in the stronger acid trifluoromethane-sulfonic acid (TFSA). Similar results were obtained if benzene was replaced by toluene or anisole. The authors suggested that the reaction in TFA proceeded through O-protonated hydroxylamine either via a direct Sn2 displacement on N by the aromatic nucleophile or via attack of the aromatic compound on the N of a nitrenium ion. In TFSA they favored a mechanism in which the diprotonated hydroxylamine lost water to generate an iminium-benzenium dication (11, Scheme 5), a protonated nitrenium ion. " This... 

Takeuchi and co-workers showed that the ratio of N- to C-substitution on the apparent intermediate 75a by a series of aromatics in arene/TFA mixtures was sensitive to the structure of the precursor to 75a (phenyl azide, N-phenylhydroxylamine or O-trifluoroacetyl-N-phenylhydroxylamine) even though the decomposition rates of these precursors were unaffected by the identity of the arene. This result is consistent with the characterization of 75a from N3 and Br trapping studies as a short-lived intermediate that will usually react through ion pair or preassociation processes that may be leaving-group dependent. ... 

In the complex tris(jV-benzoyl-jV-phenylhydroxylamine)chromium(III) the ligand acts as a bidentate two O donor.616... 

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