Hydroxylamines 0-benzyl

Hydroxylamin 0-Benzyl-N-(3-brom-2,2-dimethyl-propyl)- E16a, 278 (Oxim-Red.)... 

Scheme 4.73 The catalytic enantioselective conjugate addition of hydroxylamine benzyl ether to an A -enoylpyrazole.

Allyl or benzyl groups on the nitrogen facilitate the process. The rearrangement appears to be intramolecular (13), proceeding by a cycHc mechanism as in the case of /V-2-buteny1-/V-metby1 aniline oxide giving /V-methyl-0-1-methylallyl-/V-phenyl-hydroxylamine. 

Diphenylthiirene 1-oxide reacts with hydroxylamine to give the oxime of benzyl phenyl ketone (79JA390). The reaction probably occurs by addition to the carbon-carbon double bond followed by loss of sulfur monoxide (Scheme 80). Dimethylamine adds to the double bond of 2,3-diphenylthiirene 1,1-dioxide with loss of sulfur dioxide (Scheme 81) (75JOC3189). Azide ion gives seven products, one of which involves cleavage of the carbon-carbon bond of an intermediate cycloadduct (Scheme 81) (80JOC2604). 

Shaw and McDowellhave prepared imidazolone derivatives by cyclization of a-acylamino amides. In a variation of this reaction the azlactone (30) was gradually converted to the hydroxamic acid (31) by methanolic hydroxylamine. Sodium methoxide and hydroxylamine readily gave the acyclic hydroxamic acid (32) which could be cyclized to 31 by dilute acid. Benzyloxyurea has been used in the sjrnthesis of pyrimidine hydroxamic acids (33) by reaction with /S-diketones followed by catalytic hydrogenation of the benzyl group. Protection... 

Furthermore the formation of <9-substituted hydroxylamines 12, e.g. by migration of an allyl or benzyl substituent, is possible ... 

Colorimetric assay with hydroxylamine showed this salt to contain 94% of the anhydrous penicillin. Paper chromatography showed complete reduction of the benzyl group. 

Manche Hydroxylamine, z. B. N-Benzyl-hydroxylamin, werden durch Basen zum Amin und Oxim disproportioniert. In solchen Fallen hydrolysiert man unter sauren Bedingun-gen. 

O-Methy l-N-benzyl-hydroxylamin O-tert. -Butyl-N-benzyl-hydroxyl-... 

O, N- Dibenzyl-hydroxylamin 0-Methyl-N-(4-chlor-benzyl)-hydroxylamin... 

Benzaldehyd-oxim + Essigsaure —> N-Athyl-N-benzyl-hydroxylamin 56% d.Th. 

Bei der Reduktion an Quecksilber von Benzaldoxim zvtN-Benzyl-hydroxylamin wird in Phosphatpuffer-Losung bei 0° gearbeitet6. 

N-Diphenylmethylen- 374 N-Diphenylmethylen-O-aminocarbonyl- 612 N-[l,3-Diphenyl-propyl-(2) - 374 N-[l,3-Diphenyl-propyliden-(2)]- 374, 377, 380 N-(4-Halogen-phenyI)- 683 N-Heptyl- 375 N-Heptyl-N-acetyl- 376 N-Heptyliden- 375 N-Hcptyliden-O-acetyl- 376 0-(2-Hydroxy-athyl)-N-athoxycarbonyl- 133 N-(4-Hydroxy-phenyl)- 683 0-(2-Hydroxy-l-phenyl-athyI)-N-athoxycarbonyI-aus 0-(ci-AthoxycarbonyI-benzyl)-N-athoxycar-bonyl-hydroxylamin und Lithiumalanat 133 N-Isopropyl- 682 N-Isopropylidcn- 613 N-Methyl- 133, 682 O-Methyl-N-bcnzyliden- 377 O-Methyl-N-benzyliden- 375 0-Methyl-N-(4-chlor-benzyl)- 375 0-Methyl-N-(4-chlor-benzyliden)- 375 N-Methy -N,0-diacetyI- 682 N-(4-Methyl-phenyl)- 683 0-McthyI-N-( 1 -phenyl-athyliden)- 375 N-(4-Methylthio-phenyl)- 684 N-(4-Nitro-benzyl)- 374 N-[4-Nitro-benzyliden - 374, 377 N-(2-Nitro-phenyl)- 562 N-(4-Nitro-phenyl)- 682 N-Nitroso-N-cyclohexyl- 697 N-Octyl- 374 N-Octyl-(2)-N-acetyl- 376 N-Octyliden- 374 N-0ctyliden-(2)-0-acctyl- 376 N-(Pentafluor-phenyl)-0,N-diacetyl- 697 N-Phenyl- 474, 481, 682, 783 N-Phenylacetyl-O-benzoyl- 265 N-(l-Phenyl-athyl)- 374 N-(l-Phenyl-athyl)-N-acetyl- 376 N-(l-Phenyl-athyliden)-374, 613 N-( l-Phenyl-athyliden)-0-acetyl- 376 N-[ 1 -Phenyl-buten-( 1 )-yl-(3)-iden]- 582 N-f4-Phenyl-butyl-(2)-iden]- 581 N-Phcnyl-N,0-diacetyl- 682 N-(4-Phenylthio-phenyl)- 684 N-Propyl-N-cyclohexyl- 376 N-Propyl-N-isopropyl- 376 O-Sulfonyl- 481 N-(4-Sulfonyl-phenyI)- 683 N-(2-Vinyl-phenyl)- 698... 

The organosilane reduction of hydrazones to hydrazines is readily accomplished in good yields with Et3SiH/TFA (Eq. 336).560,561 (V-Tosylimines294 are reduced to their A-Boc tosylamino counterparts,294 and are also reduced with (MeO)3SiH/LiOMe in good yields.294 Benzyl-protected hydroxylamines are reduced with PhMe2SiH/TFA.551... 

In the mechanism study of /V-benzyl-/V -alkyl hydroxylamines, regarding oxidation with HgO and p-benzoquinone, it has been proposed on the basis of intra- and intermolecular kinetic isotope effects that, initially, there takes place a one-electron transfer from a nitrogen atom to the oxidant, with a subsequent proton abstraction (106—108). 

The chirality source in the synthesis of optically active nitrones (71) and (72) are known to be enantiopure chiral benzyl type hydroxylamines, (f )-a-methyl-benzylhydroxylamine (70a) and (f )-a-(hydroxymethyl)-benzylhydroxylamine (70b) (Scheme 2.25) (221). 

Nucleophilic addition of organometalic reagents occurs when the nitrone form is in equilibrium with the hydroxylamine form, for instance, in the case of N -benzyl-/V-glycosyl hydroxylamines (Scheme 2.130) (213). 

Transformation of chiral nitrones into enantiomer enriched a-chiral N -hydroxylamines and their derivatives, has been successfully employed in the enantioselective synthesis of (+ )-(R)- and (—)-(S)-zileuton (216). An expeditious synthesis of thymine polyoxin C (347), based on the stereocontrolled addition of 2-lithiofuran (a masked carboxylate group) to the A-benzyl nitrone derived from methyl 2,3-O-isopropylidene-dialdo-D-ribofuranoside, is described (Scheme 2.151) (194). 

W-benzyl-TV-hydroxylamine)phenylmethyl]-3-hydroxybutanoate (398) (637). The absolute configuration (398) was determined as (aRfiS,yR) thus, diastere-oselective addition of ketene silyl acetals (397) to nitrone proceeds as anti-a, p-anti-p, y (Scheme 2.176). 

Electrochemical reduction of benzylic nitro compounds (27) in an ethanolic aqueous acetic acid buffer (35 65) affords a mixture of the corresponding oxime and hydroxylamine (equation 6)48. The hydroxylamine can subsequently be oxidized back to the oxime (28) (via the intermediate nitroso compound) conversions as high as 90% can be obtained. 

O-Nitrosocarbonyl compounds (nitrosoformates) 187 (R = t-Bu or Bn) are obtained from the hydroxylamines ROCONHOH. They can be trapped by reaction with butadiene to give the cycloadducts 188 (equation 107). With 9,10-dimethylanthracene the benzyl... 

Alkylation of hydroxylamine with primary halides and sulfonates is rarely used nowadays for preparation of A-alkylhydroxylamines due to the competing formation of N,N-dialkylhydroxylamines. A number of older procedures have been reported with low to moderate yields of Al-alkylhydroxylamines. Yet, in many cases the reported low yields can be attributed to workup losses during distillation and crystallization steps rather than to the polyalkylation. Use of excess of hydroxylamine in reactions with primary alkyl halides (e.g. 3) improves the yields of monoalkylation (equation 2). Most of the examples of alkylation of hydroxylamine in good yield involve a substitution of an activated halogen atom at benzylic positions as well as in haloacetamides 4 leading to alkylhydroxylamines such as 5 where dialkylation rates are lower (equation 3). 

Intramolecular addition of hydroxylamines and hydroxamic acids to the non-activated double bonds is possible through oxidative cyclization. Reaction of O-Acyl fi,y-unsaturated hydroxamates (e.g. 56, equation 38) with bromine provides 3,4-substituted iV-hydroxy -lactams such as 57 with high diastereoselectivity. Analogous reaction of O-benzyl hydroxylamine 58 (equation 39) with iodine results in five-membered cyclization with 2 1 ratio of diastereomers. ... 

Diastereoselective [2,3]-sigmatropic rearrangement of lithium O-allyl-A-benzylhy-droxylamides (195) bearing a stereogenic center adjacent to the migration terminus was reported 3" 3 (equation 57). When the (E) and (Z)-iV-benzyl-0-(4-methoxy-4-phenylbut-2-enyl)hydroxylamines (194) rearrange, a chelation by the lithium ion occurs and the (Z)-(lR5, 2R5 )-l-phenyl-l-methoxy-3-iV-benzylaminobut-3-ene (196) is the major product... 

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