O-arylhydroxylamine

O-Alkyl- and O-arylhydroxylamines and their A-substituted derivatives have been the most extensively used reagents for amination of C-nucleophiles (Table 1). O-Methyl hydroxylamine la is the most extensively used O-organylhydroxylamine-type reagent. 

The A-acyl-O-arylhydroxylamine 166 rearranges in the presence of trifluoroacetic acid to 168 by a [3,3]-sigmatropic shift. An isourea intermediate 167 was proposed to explain the observed transformation (equation 49). 

High yields of 3-aminocoumarins (390) are formed rapidly when solutions of dimethyl butynedioate and O-arylhydroxylamines are mixed at low temperature (72TL3941). Their formation has been rationalized through a rearrangement of the substituted hydroxylamines (389). 

Sheradsky and Lewinter39 have reported a fascinating transformation involving the reaction of O-arylhydroxylamine (58) and DMAD. The initially formed Michael adduct (59) undergoes valence tautomerism to 60, which gives rise to 3-amino-4-carbomethoxycoumarins (63), through the phenol intermediate 61 (Scheme 8). 

A series of o-arylhydroxylamines, which are interesting intermediates for the preparation of benzofurans, hydroxybiphenyls, and catechols, have been synthesized starting from Cr(CO)3-activated fluoroarenes. Oxime 21 reacts with m-fluorotoluenetricarbonylchromium... 

Ring expansion of phenols. Theilacker heated the sodium salt of 2,6-dimethyl-phenol with chloramine in a fusion with an excess of the dimethylphenol and obtained in about 50% yield a crystalline product originally assumed to be the O-arylhydroxylamine, ArONH, but recognized by Paquette as a l,3-dihydro-2H-azepin-2-one (see 3, below). The reaction is generally applicable to 2,6-disub-stituted phenols. A procedure by Paquette for the conversion of 2,4,6-trimethyl-phenol (1) into l,3-dihydro-3,5,7-trimethyl-2-H-azepine-2-one (3) is as follows. 

The electrophilic amination of the sodium salts of a-unsubstituted 3-dicarbonyl compounds is one of the few examples of an amination where hydroxylamine O-sulfonic acid gives useful yields (Eq. 161) 472 with two equivalents of the substrate, pyrroles are formed.472,473 Chloramine,62 64 O-arylhydroxylamines,93,124,474 O-sulfonylhydroxylamines,134 and 0-(diarylphos-phinoyl)hydroxylamines106,139,475 have also been employed, although a low yield and formation of the hydroxylation product as a side product have been reported in one instance with (4-Me0C6H4)2P(0)0NH2.145 Some of these animations use chiral auxiliaries in the substrates with modest diastereoselectivities,124,475,476 but these have been superseded by the catalytic methods discussed below. 

Replacing phenylhydrazine by an O-arylhydroxylamine derivative (p. 511) leads to benzofurans phenylhydroxylamine hydrochloride and a ketone may be similarly cyclized in acetic acid-sulphuric acid or in 98% sulphuric acid. 

Synthesis of 0-Arylhydro iylamines. Reaction of tricarbo-nylchromium complexes of aryl halides (1) with TYf-butoxycarbo-nylhydroxylamine (2) in DMSO and powdered KOH under N2 at rt resulted in the nucleophilic substitution of the Cl to give the corresponding tricarbonyl[(/-butoxycarbonylaminoxy)arene]chro-mium complexes (3) (eq 3). Consecutive I2 treatment and acid hydrolysis gave the O-arylhydroxylamines in high overall yields. ... 

Synthesis.— The preparation of a-amino-acids from a-halogeno-acids and ammonia is often unsatisfactory owing to the occurrence of multiple alkylations etc. A way around this problem is to treat a-halogeno-esters with alkali-metal cyanates and an alcohol this gives N-alkoxycarbonyl-a-amino-esters in >90% yield. " The O-arylhydroxylamine (148) is a useful reagent for aminating enolates, especially those derived from malonic esters, which can thus be... 

Acylhydrazines R1 CONF1NF1R2 (R1 = Ph or PhCH2 R2 = Bu, PhCH2 or Ph) are produced by the action of hydroxamic acids R ONHOH on the primary amines R2NH2 in the presence of tosyl chloride or 2-chloro-l-methylpyridinium chloride94. O-(Diphenylphosphinoyl)-A-arylhydroxylamines 77 (R = NO2, Ac, Tos or CN) react with A-methylaniline to afford the hydrazine derivatives 7895. 

The oxidation of arylhydroxylamines and their O-alkylated derivatives to the corresponding nitro compounds can be achieved with both ozone and nitric acid. This strategy is a useful alternative to the oxidation of arylamines. 

Polynitroarylenes containing a variety of leaving groups are very susceptible to nucleophilic displacement (Section 4.8), and so, treatment of such substrates with hydroxylamine or an alkoxyamine usually generates the corresponding arylhydroxylamine or its O-alkyl derivative. 

Nielsen and co-workers studied the oxidation of arylhydroxylamines and their O-methyl derivatives with ozone in inert solvents at subambient temperature. 1,2,3,5-Tetranitrobenzene (54) is formed in quantitative yield from the oxidation of both N-hydroxy-2,4,6-trinitroaniline... 

Addition of arylhydroxylamines to electrophilic allenes such as methyl propadienoate or l-methancsulfonyl-l,2-propadiene is another route to O-vinyl derivatives[2]. The addition step is carried out by forming the salt of the hydroxylamine using NaH and the addition is catalysed with LiO,CCF3. The intermediate adducts are cyclized by warming in formic acid. Yields are typically 80% or better. 

The asymmetric aziridination of a, P-unsaturated carboxylic acid derivatives is a direct route to optically active aza-cyclic a-amino acids, and this class of chiral aziridines can also be used as chiral building blocks for the preparation of other amino acids, P-lactams, and alkaloids. Prabhakar and coworkers carried out an asymmetric aziridination reaction of tert-butyl acrylate with O-pivaloyl-N-arylhydroxylamine 25 in the presence of cinchonine-derived chiral ammonium salt 2e under phase-transfer conditions, which furnished the corresponding chiral N-arylaziridine 26 with moderate enantioselectivity (Scheme 2.24) [46],... 

Alkylation of arylhydroxylamines. The trimethylsilyl ether of phenylhydroxylam-ines undergo nucleophilic o- and p-alkylation with trialkylaluminums. Only N- lkylation occurs in the absence of the trimethylsilyl group. This reaction is particularly useful for preparation of o-alkynyl derivatives of aromatic amines, which provide a convenient access to indoles. 

Hydroxylamines usually react with acid chlorides to give mixtures of N-, O- and poly-acylated products. In contrast reaction of tris(trimethylsilyl)hydroxylamine (65) with aliphatic acid chlorides leads selectively under /V-monoacylation to the corresponding hydroxamic acids (66 equation 26). While di-phenylphosphinic chloride (68) is attacked by the oxygen of hydroxylamine to yield 0-(diphenylphos-phinyl)hydroxylamine (67 Scheme 13), A -(diphenylphosphinyl)hydroxylamine (69) can be obtained by treatment of diphenylphosphinic chloride with 0-trimethylsilylhydroxylamine followed by removal of the silyl blocking group (Scheme 13). 0-Acylation of arylhydroxylamines can be achieved with acyl cyanides. ... 

Conversion of Arylhydroxylamines into o-Aminophenols by Various Liver Preparations... 

The direct Au-catalyzed synthesis of 2-arylindoles from aryl alkynes and o-iodoanilines was reported by Wang (eqnation 3) [17]. The An-catalyzed double hydroamination of o-alkynylanilines and terminal alkynes was fonnd by Li to give A-vinylindoles [18], Patil used a Au-catalyzed one-pot reaction between o-alkynylanilines and alkynols to give various 3-substituted indoles [19]. Zhang fonnd that both A-arylhydroxylamines [20] and... 

Cordova and co-workers developed a highly enantioselective three-component synthesis of isoxazolidines 266. The reactions were carried out between A -arylhydroxylamines, aldehydes and o,(i-unsaturated aldehydes, Scheme 3.84 [106],... 

Scheme 14.10 Rearrangements of O-vinyl-jV-arylhydroxylamines for the preparation of interrupted Fischer-indole intermediates.—...

Rearrangements related to the Bartoli-indole synthesis have also been designed for the preparation of ortho-alkylated anilides and oxindoles from O-acetyl-JV-arylhydroxylamines. 

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