Reaction with nitrosobenzenes

If the substituent at C-l of the diene is an aldehyde group, the reaction with nitrosobenzene proceeds with total regio- and stereoselectivity, but the intermediate dihydro-1,2-oxazine 12 is unstable, leading to a number of decomposition products. The regioselectivity of the addition, however, is in agreement with the predictions of FMO theory66. 

A surprising result is observed when 2//-pyran-2-thione is employed as diene in the hetero-Diels- Alder reaction with nitrosobenzene. The adduct 7 is stereoselectively formed and immediately converts through a number of steps to give 8 in practically 100% yield. The structure of 8 was assigned on the basis of H-NMR spectroscopy and X-ray66 87 88. 

Bis(silyl)ketene acetals undergo silatropic ene reaction with nitrosobenzene to give N-hydroxyamino acid derivatives. When allylmagnesium chloride is reacted with nitroarenes, unstable adducts result. Reduction of these adducts with LAH in the presence of palladium on charcoal leads to A -allyl-W -aryl-hydroxylamines (73 Scheme 15). With alkyl Grignard reagents this reaction is negligible. ... 

Phenyl-substituted cyclopentadienylides also undergo Wittig-type reactions with nitrosobenzene, [135,149,156,168], e.g. 

In the reaction with nitrosobenzene, azoxybenzene and Ni(PhN02>2 are formed. The nickel complex is an interesting example of a" coordination compound of a nitro derivative with a zerovalent metal. The X-ray analysis of this compound has been undertaken 383, but the final structure has not yet been reported. The reaction with Bu NC can be carried out catalytical 1y. Thus a mixture of PhNO and Bu NC in benzene, in the presence of a catalytic amount of NiCBu NO at reflux, produces Bu NC0( SOX based on PhNO) along with PhN=C=NBu, PhN=NPh and [Pg.105]

Since from 2-n i trobi phenyl, carbazole [see eqA36)] was obtained in 37.5% yield, an arylnitrene intermediate was suggested. Such labile organic intermediate is presumably bound to iron.This species could produce azobenzene by coupling, azoxybenzene by reaction with nitrosobenzene formed by reduction of nitrobenzene (3.2.1.), amines by hydrogen abstraction and polymeric tars by decomposition. 

Radical and miscellaneous reactions— The photochemical reactions of alkenylpyridines discussed involve radical intermediates. The same may be true of the conversion by irradiation or reaction with nitrosobenzene of 2 -nitrotolazole into an isatogen ... 

Aldehydes and ketones could be asymmetrically a-amino-oxylated [36, 37] or a-aminated [38] to corresponding poly-functional compounds 8 and 9 by proline-catalyzed reactions with nitrosobenzene or diethyl azodicarboxylate in molten imidazoUum salts (Scheme 22.5). As compared to those in common solvents, the yields of a-aminoxylation products 8 of both aldehydes and ketones improved significantly in the IL medium and the enantioselectivity was excellent Yields and enantiomeric enrichment of hydrazino-aldehydes 9 were somewhat lower. The ionic environment considerably accelerated the processes and the (S)-proline/IL system could be quantitatively recovered after completion of the aminoxylation reaction and reused (5-6 times) without any loss of catalytic performance. Aldehyde-derived products 8 and 9 (R = H) could be reduced to chiral 1,2-diol derivatives 10 or configurationally stable heterocycles 11, which are valuable intermediates in asymmetric synthesis. 

Primary synthesis of arylazopyrimidines is used (52JCS3448). It is exemplified in the condensation of phenylazomalondiamidine with diethyl oxalate to give the azopyrimidine (833) (66JCS(C)226). Finally, 5-phenylazopyrimidine may be made by the condensation of pyrimidin-5-amine with nitrosobenzene (5UCS1565) but the reaction seems to have been overlooked for many years. 

IH-Azepine, 1-methoxy carbonyl-cycloaddition reactions, 7, 522 with nitrosobenzene, 7, 520 tricarbonyliron complex acylation, 7, 512-513 conformation, 7, 494 tricarbonylruthenium complex cycloaddition reactions, 7, 520 1 H-Azepine, l-methoxycarbonyl-6,7-dihydro-synthesis, 7, 507... 

Pyridotriazinone 70 was obtained by the reaction of iV-(2-pyridyl)benzoylacetamide 119 with nitrosobenzene in methanol. The reaction probably involves the attack of two molecules of nitrosobenzene at C-2 of 119 with cleavage of C(l)-C(2) and C(2)-C(3) bonds affording diphenylcarbodiimide and 2-pyridylisocyanate, which undergo a [4+2] heterocycloaddition. Interestingly, the reaction of acetyl analog of 119 did not afford the corresponding bicyclic product, instead, 2-methoxy-2-phenylamino-iV-(2-pyridyl)acetoacetamide was obtained (Equation 14) <2004S2975>. 

The condensation of nitrosobenzene with phenylhydroxylamine which is described below is an example of this similarity. Hydroxyl-amine and phenylhydrazine also react with nitrosobenzene, but the details of these reactions cannot be given here. 

Reactions of nitrosobenzene with aliphatic amines185 yield (phenylazo)alkanes and azoxybenzene as the main products. The adduct 67 is assumed to be an intermediate in obtaining both products, as seen in Scheme 3. 

A similar mechanism of addition was presumed for the reaction of nitrosobenzene with OH-. How-... 

Collectively, the data from in vitro and in vivo experiments confirm the reactions of nitrosobenzene with thiols as observed in mere chemical systems. 

The pH-rate profile for reaction of nitrosobenzene with A-methylhydroxylamine (to form only 1-methyl 2-phenyldiazene-2-oxide) has been found to exhibit a negative break between pH 0.5 and 3.0. This has been ascribed to a change in ratedetermining step from nucleophilic attack on nitrosobenzene at low pH to dehydration of the A,iV -dihydroxy intermediate at higher pH the dehydration is subject to general-acid catalysis a = 0.34) and specific and general-base catalysis (f) = 0.20). The pH-rate profile is similar to that for reaction of A-methylhydroxylamine with... 

Momiyama and Yamamoto" have further expanded the utility of H-bond-mediated reactions catalyzing nitrosobenzene addition to enamines using TADDOL 38 or hydroxy acid 39 as catalysts. Remarkably, the judicious selection of H-bond-catalyst/enamine combination resulted in the formation of only A-addition compounds with TADDOL 38 (Scheme 11.14e), while acid 39 furnished exclusively O-nitroso aldol products (Scheme 11.14f). 

Reduction of substituted nitrobenzenes under alkaline conditions, usually with aqueous sodium acetate as electrolyte and a nickel cathode, is the classical method due to Elbs [45] for the formation of azo- and azoxy-compounds. Protons are used in the electrochemical reaction so that the catholyte becomes alkaline and under these conditions, phenylhydroxylamine reacts rapidly with nitrosobenzene to form azoxybenzene. Finely divided copper has long been known to catalyse the reduction of nitrobenzene to aniline in alkaline solution at the expense of azoxybenzene production [46]. Modem work confirms that whereas reduction of nitrobenzene at polycrystalline copper in alkaline solution gives mainly azoxybenzene, if the electrode is pre-oxidised in alkaline solution and then reduced just prior to the addition of nitrobenzene, high yields of aniline are obtained with good current efficiency... 

The preparation of A-phenyl-substituted hydroxamic acids 125 in the reaction of formaldehyde with nitrosobenzene to give 124 is strongly catalyzed by Fe + ions, which stabilize the transition states 126 and 127 for the rate-controlling proton transfer from the carbon atom of nitrosocarbinolic cation intermediate 125 leading to the product 128 (Scheme 62) . 

Reaction of nitrosobenzene with oxazoles (210) affords 5-acyloxadiazolines (211) (Scheme 91) <91CL1221>. 

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