A-Nitroso reagents

Synthesis of Chiral Reagents. An efficient chiral a-chloro-a-nitroso reagent derived from 10-camphorsulfonyl chloride (1, Cy2NH 2, NH2OH 3. t-BuOCl 70-78%) has been developed for the asymmetric a-amination of ketone enolates (eq 7). The resulting p-keto /V-hydroxylamine can be converted to the anti-1,2-hydro y amine under reducing conditions (NaBHt Zn, HCl, AcOH),... 

Scheme 8.26. Reaction of an achiral enolate with a chiral a-chloro-a-nitroso reagent [113],...

Chiral a-nitroso reagents anti-/3-amino alcohols. The a-chloro-a-nitroso reagent 2 is prepared from the 10-camphorsulfonamidc I in 78% yield by oximation followed by chlorination. This reagent reacts with the zinc enolate (a) of an ethyl... 

With a peroxyacid, the reagent used in their preparation, oxaziridines further react to yield aliphatic nitroso compounds. An electrophilic attack to ring nitrogen is plausible, leading to an intermediate oxaziridine N-oxide (81), which immediately decomposes to a nitroso compound and an aldehyde (57JA6522). 

Some time ago Tedder (1957) recommended a process which he called direct introduction of the diazonium group , because it replaces the steps of nitration, reduction, and diazotization of an aromatic compound by a one-pot operation with three equivalents of a nitrosating reagent in acidic solution. The first step (Scheme 2-35) is a C-nitrosation and the following steps (Scheme 2-36) are the reduction of the nitroso-arene. 

These radical anions have been detected by ESR. This mechanism is consistent with the following result when nitrosobenzene and phenylhydroxylamine are coupled, and N labeling show that the two nitrogens and the two oxygens become equivalent. Unsymmetrical azoxy compounds can be prepared by combination of a nitroso compound with an N,N-dibromoamine. Symmetrical and unsymmetrical azo and azoxy compounds are produced when aromatic nitro compounds react with aryliminodimagnesium reagents, ArN(MgBr>2. ... 

Azoxy compounds can be obtained from nitro compounds with certain reducing agents, notably sodium arsenite, sodium ethoxide, NaTeH, NaBH4—PhTeTePh, and glucose. The most probable mechanism with most reagents is that one molecule of nitro compound is reduced to a nitroso compound and another to a hydroxylamine 119-42), and these combine (12-51). The combination step is rapid compared to the reduction process. Nitroso compounds can be reduced to azoxy compounds with triethyl phosphite or triphenylphosphine or with an alkaline aqueous solution of an alcohol. ... 

Acetylene compounds Dicobaltoctacarbonyl Formation of colored complexes. After the reagent excess has been washed out, reaction with bromine vapor yields cobalt bromide, which reacts with a-nitroso-P-naphthol to yield red chromatogram zones on an almost colorless background. [11]... 

Note Monohydroxybenzene derivatives and vicinal hydroxymethoxybenzene derivatives do not react under these conditions but can be made visible by spraying afterwards with Folin-Qocalteu s reagent [1]. Flavonoids, anthraquinone derivatives and a-nitroso-B-naphthol yield a red color with alkalis alone [1]. Steroids and aromatic amines do not react [1]. 

A method involving SPE was developed for the determination of ten A-nitroso amino acids in cured meat products. These compounds were derivatized with diazomethane followed by O-acylation of hydroxyl groups with acetic anhydride-pyridine reagent. The methyl esters and their acylated derivatives were separated by GC on a DB-5 fused silica capillary column and quantified with a TEA-CLD specific for the nitric oxide derived from the thermal denitrosation of nitrosamines recovery exceeded 75% at the 10 ppb level579. 

A method for the preparation of unsymmetrical azoxy compounds involves the reaction of certain diimide dioxides with Grignard reagents [5]. This reaction has somewhat limited applicability because the diimide dioxides which were used were prepared by alkylation of organonitrosohydroxylamines, a class of compounds of which cupferron is perhaps the best-known example. The reaction is, in effect, a reduction of a diimide dioxide to an azoxy compound by use of a Grignard reagent. The overall process is represented by Procedure 2-3. Since the starting materials are, in effect, unsymmetrically substituted nitroso dimers, extension of the reaction to nitroso dimers would be interesting. 

A-Halogeno-, A-nitroso- and hence A-amino-azetidines have been prepared from azetidines by reaction with positive halogen reagents and nitrosating agents, respectively (Section 5.09.2.2.3). 

Some of the most important reactions of amines are brought about by nitrous acid (HONO). The character of the products depends very much on whether the amine is primary, secondary, or tertiary. In fact, nitrous acid is a useful reagent to determine whether a particular amine is primary, secondary, or tertiary. With primary amines nitrous acid results in evolution of nitrogen gas with secondary amines insoluble yellow liquids or solid 7V-nitroso compounds, R2N—N=0, separate tertiary alkanamines dissolve in and react with nitrous acid solutions without evolution of nitrogen, usually to give complex products ... 

The nitrosochlorination of alkenes has been reviewed.146 The products of nitrosochlorination are often dimers due to the propensity of nitroso groups to couple with one another. For this reason, and because of the advent of newer reagents, modem synthetic uses of NOC1 are scarce. Instances where NOC1 has proven to be a useful reagent include the preparation of a-oximinocarbonyl compounds (Scheme 71)147 and the synthesis of precursors of insect growth regulators (Scheme 72).148... 

The 1,3 dipole diazomethane is a mild reagent to furnish methyl esters (see Chapter 13), but it has some disadvantages, too it is volatile, toxic and furthermore explosive. For this reason it has to be prepared by reaction of KOH with 7V-methyl-7V-nitroso-/ ara-toluenesulfon-amide (carcinogenic ) or in situ.11 Another simple method to protect the COOH functionality of the neuraminic acid is the esterification with methanol as solvent and reactand under H+ catalysis e. g. ion exchanger. 

Attempts to extend these reactions to the synthesis of simple hydroxylamines were plagued by deprotonation and redox side-reactions, but recently yields have been much improved by conversion of the Grignard reagent into an organocerium reagent in situ [12] for example, yV-butyl-A-propylhydroxylamine was prepared in 90% yield. Another successful variant utilized A-nitrosodiphenylamine to generate a nitroso compound in situ. The hydroxylamine salt produced was oxidized in situ to give a nitroxide [13] ... 

The reagent consists of a 1 per cent solution of a-nitroso-/ -naphthol in 50 per cent acetic acid, or in ethanol, or in acetone. 

The reaction of a carboxylic acid with diazomethane is mild and efficient Diazomethane is usually prepared by reaction of potassium hydroxide with N-methyl-A/-nitroso-p-toluenesulfonamide (HAZARD carcinogenic) and used in ether solution since it is volatile, toxic, and explosive.44 Therefore, the method is most suitable for small scale reactions. A useful feature of the reaction is that diazomethane is intensely yellow and the consumption of the reagent is easily detected by the disappearance of the colour. It may be convenient to prepare the diazomethane in situ 45 (Trimethylsilyl)diazomethane is a safer alternative to diazomethane for the preparation of methyl esters and it is commercially available as a 2.0 M solution in hexanes,46 47... 

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