Nitrosobenzene, reaction with

Nitrosobenzenes react with the carbonyl group of aldehydes to yield hydroxamic acids 73, according to reaction 20. Recently, the reactions between some X-substituted nitrosobenzenes (X = H, p-Me, p-C 1, m-Cl, p-Br) and formaldehyde were reported194 in order to investigate the mechanism of the hydroxamic acid formation. The mechanism reported in Scheme 9 involves a first equilibrium yielding the zwitterionic intermediate 74 which rearranges (by acid catalysis) into hydroxamic acid 75. The presence of a general acid catalysis, the substituent effect (p values of the Hammett equation equal —1.74),... 

Nitroso compounds are seldom used as dipolarophiles for trapping reactions with thiocarbonyl ylides. However, Sheradsky and Itzhak (175) did report one example where nitrosobenzene reacts with a thioisomiinchnone to give 134 as the major product. 

Hydrogen bond-promoted asymmetric aldol reactions and related processes represent an emerging facet of asymmetric proton-catalyzed reactions, with the first examples appearing in 2005. Nonetheless, given their importance, these reactions have been the subject of investigation in several laboratories, and numerous advances have already been recorded. The substrate scope of such reactions already encompasses the use of enamines, silyl ketene acetals and vinylogous silyl ketene acetals as nucleophiles, and nitrosobenzene and aldehydes as electrophiles. 

In 2002, Yamamoto and Momiyama reported an unusual aldol-like reaction with silyl enol ethers and nitrosobenzene in the presence of a catalytic amount of TESOTf (nitrosoaldol reaction).29 Usually, nucleophiles react with nitrosobenzene without Lewis acid to give the N adduct predominantly. In contrast, they reported that the reaction of silyl enol ethers and nitrosobenzene catalyzed by TESOTf afforded the... 

Morpholino-li/-2-benzopyran-l-one (208) adds aromatic aldehydes in hot acetic acid or acetonitrile to form dihydro-4-morpholinocarbonyl-l/7-2-benzopyran-l-ones 209 as mixtures of cis- and trans-isomers. The process is formally an ene reaction in which an acyl group is transferred (equation 88). Analogous reactions with imines, phenyl isocyanate, nitrosobenzene, arenediazonium salts and carbon disulphide lead to a variety of heterocycles (Scheme 7)110. 

Tetrafluoro(perfluorophenyl)silicates, M [CgF5SiF4]. obtained by the interaction between trifluoro(perfluorophenyl)silanc and metal fluorides MF (M — K. Cs) or tetramethylam-monium fluoride in nonaqueous acetonitrile or diglyme,are excellent reagents for penta-fluoroarylation with formation of pentafluoro-substituted derivatives of benzene. Thus, the reaction of these salts with nitrosonium and nitronium tetrafluoroborates leads to per-fluoro(nitrosobenzene) (14) and perfluoro(nitrobenzenc)(15), respectively, in quantitative yield. In the case of reaction with perfluoropyridine, perfluoro(4-phenylpyridine) (16) (33% yield) and pentafluorobenzene (.37 % yield) arc formed. Reaction of tetramcthylammonium tetrafluo-ro(perfluorophenyl)silicate with bromine or iodine pentafluoride gives the corresponding bro-mopentafluorobenzene and pentafluoro(tetrafluoroiodo)benzene. ... 

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. 

When acylnitroso derivatives are employed as dienophiles in the cycloaddition, the re-gioselectivity of the reaction is inverted with respect to the mode of addition of nitrosobenzene. Thus l,2-dihydro-A -methoxycarbonylpyridine. by reaction with V-acylhydroxylamines in the presence of tetraalkylammonium periodate at 78 r C in dichloromethane, leads to the corresponding 2-oxa-3,5-diazabicyclo[2.2.2]oct-7-enes in good yield. The regiochemistry of the cycloaddition product 2 was determined by 13C NMR84-86. 

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. 

The resulting anion can then carry out a nucleophilic reaction with the electrophilic nitrogen of the nitroso group of nitrosobenzene. 

The oxidants dimethyl sulfoxide and nitroso compounds react easily with oL-bromo ketones and convert them into a-dicarbonyl compounds. The reaction with nitroso compounds is usually carried out in the presence of pyridine and proceeds through a nitrone stage. Phenacyl bromide (a-bromoacetophenone) is thus transformed first into phenacylpyridinium bromide and further, with nitrosobenzene, into a-ketoaldonitrone, which is subsequently treated with hydroxylamine to give phenylglyoxal monoxime or with phenylhydrazine to give phenylglyoxal osazone [985] (equation 411). 

Ylides may react with nitrosobenzene in a similar fashion to their reactions with carbonyl compounds (equation 12). Sulphonium ylides give nitrones phosphonium... 

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. ... 

Nitrosobenzene was also used as a quantitative spin trap for phenyl free radicals, to study their involvement in arylation reactions with organobismuth reagents. Again, ESR observations indicated the formation of phenyl free radicals. However, quantitative trapping measurements showed that only a small amount of free radical derived adducts (2-3%) was formed. The yield of C-arylated products was not affected by the presence of this free radical trap. ... 

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