Aryl nitroso compounds

Synthesis front Nitroso Compounds Aryl nitroso compounds (175) react easily with dimethyl bromomalonate in the presence of alkali to give the corresponding A-aryl-QC-dimethoxycarbonyl-nitrones (177) (Scheme 2.62) (333). 

Nitroso compounds (e.g. 116, equation 85) that are unable to tautomerize to oximes undergo an ene reaction with aikenes 117 giving Af-aUylhydroxylamines 118 (equation 85). Both trifluoromethyl and aryl nitroso compounds react with aikenes although in many cases the resulting Af-allylhydroxylamines are prone to subsequent chemical transformations. If allylzinc compounds are used as the aikene components, the chemos-electivity of the reaction is reversed and O-allylation products are preferably formed . 

Figure 8. Alternate mechanistic possibility for catalysis of secondary amine nitrosation by aryl nitroso compounds...

The complexes [IrCl(CO)L2] (L = PPh3, P(OPh), both catalyze the carbonylation of aryl nitroso compounds to give isocyanates (equation 94).448... 

IX dimethyl ester Pyz = Pyrazine RImH = Imidazole with an R substituent on one of the carbon atoms RNC = Alkyl or aryl isocyanide (isonitrile) RNO = alkyl or aryl nitroso compound RPy = Substituted pyridine RTPP = 7 -phenyl substituted tetraphenylporphyrin TCeTPP = Tetra-/3,/3 -tetramethylenetetraphenyl-porphyrin TMINP = Tetrakis(o-(methylisonicotinamidophenyl)porphyrin) T(o-M)PyP = Tetrakis(methyl-o-pyridinium)porphyrin ... 

Aryl nitroso compounds, which are readily available synthetic intermediates, react regioselectively with most 1,3-dienes. Scheme 12 shows two examples of cycloadditions with unsymmetric ... 

The dihydrooxazines which are produced from aryl nitroso compounds have not found wide use in synthesis. One application to the syntheses of an N-aiyl-3-pyrrolidone is shown in equation (31). The initial Diels-Alder reaction in this sequence was totally regioselective. 

A number of cases of additions of aryl nitroso compounds to 1,2-dihydropyridine derivatives have been effected. For instance, compound (87) reacts with nitrosobenzene regioselectively and anti to the C-2 methyl group to afford adduct (88) (equation 32). 

Lastly, cells equipped of porous electrodes are useful in organic electrochemistry. Redox flow cells were efficiently developed by Moinet [55], and this concept can be considered as a great advantage toward conventional reduction and oxidation methods in organic chemistry. It is essentially because they can be particularly useful to obtain electroactive intermediates in reduction and oxidation multistep processes. A striking example had been mentioned in Sect. 6.5.1.1 in the synthesis of aryl nitroso compounds. However, the flow of the solution through the two porous electrodes is difficult to regulate. 

Aryl nitroso compounds, which are readily available synthetic intermediates, react regioselectively with most 1,3-dienes. Scheme 12 shows two examples of cycloadditions with unsymmetrical dienes, affording single isomeric 3,6-dihydro-1,2-oxazines in each case. Kresze and coworkers have examined the cycloaddition of aromatic nitroso compounds in some detail and have rationalized the orientational results of this process. It appears that, depending upon the specific nitroso compound used, the reaction transition state varies fiom nonpolar to dipolar. ... 

Synthesis of 1,2-Oxazine Derivatives. The N=0 group in certain nitroso compounds (R-N=0) is well known to function as a dienophile, and it provides easy access to the 1,2-oxazine family. However, simple alkyl nitroso compounds are generally not stable and tend to dimerize. Aryl nitroso compounds are more stable and are useful in this process. The N=0 group is also more stable with a car-boalkoxy substituent on nitrogen, and it too is useful as a dienophile (Scheme 5.11). 

Nitroso compounds and their reaction with alkenes have been very well characterized. Reactions of aryl or acyl nitroso compounds have demonstrated synthetic utility. Interestingly, reaction of aryl nitroso compounds did not display analogous selectivity to TAD nor 02 but instead displayed a selectivity of its own. Reaction of / -nitro-nitrosobenzene manifested a selectivity for abstraction from the twix group (see 88). An example of this was the conversion of 98 into 100, the only compound reported to form. ... 

Aryl nitroso-compounds make good dienophiles but are somewhat unstable. Keck and his co-workers have shown that they can be masked as the anthracene adduct and then smoothly released and transferred to an internal diene [e.g. (44) - (45)]. ° Further elaboration of (45) yielded the alkaloids ( )-heliotridine (46) and ( )-retronecine (47). 

Leskovac, V, J. Svircevic, S. Trivic, M. Popovic, and M. Radulovic. 1989. Reduction of aryl nitroso compounds by pyridine and flavin coenzymes. Int. J. Biochem. 21 825-834. 

Oxidative reactions of organonitrogen species that do not involve molecular oxygen are rather limited. The only case for which the evidence is at all convincing is the oxidation of arylhydroxylamines to arylnitroso species (Table 2). This reaction resembles the first half of the hydroxylamine oxidoreductase reaction found in nitrifying bacteria. The key difference is that the aryl nitroso compound is stable (although condensation with the arylhydroxy-lamine can occur to produce the azoxy compound, ArN(O)NAr), while the inorganic analog is nitroxyl, HNO, which if released from the enzyme would rapidly dimerize and dehydrate to form N2O. Consequently, HAO does not release the HNO or NO intermediate, but instead oxidizes it to nitrite before any substrate-derived species are released. 

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