Nitromethyl radical

The addition to alkenes of radicals derived from an a-nitroketone is also catalysed by manganese(III) [30]. During the reaction between a-nitroacetophenone 8 and m-but-2-ene, the stereochemical relationship between the methyl substituents is not preserved. The process terminates with the formation of a nitrone. A related process will generate nitromethyl radicals from nitromethane and these add to benzene to give phenyinitromethane [31],... 

Generation of Carboxymethyl and Nitromethyl Radicals by Use of Manganese Acetate as Redox Catalyst... 

Synthetically especially valuable is the oxidation of carbonyl compounds and nitroalkanes by manganese(III) salts to form carboxymethyl and nitromethyl radicals, respectively. These radicals can be trapped by olefins like 1,3-butadiene or aromatic compounds to yield synthetically interesting products. In this case it is very advantageous to generate and regenerate the oxidizing species in situ by indirect electrolysis. This was the basis for the development of a process for the synthesis of sorbic acid viay-vinyl-y-butyrolactone Equations (31)—(35) summarize the im-... 

CH3l,CH2l2 reactions at high pressures Study of i.r. spectrum of matrix-isolated nitromethyl radical... 

Manganese(III) can oxidize carbonyl compounds and nitroalkanes to carboxy-methyl and nitromethyl radicals [186]. With Mn(III) as mediator, a tandem reaction consisting of an intermolecular radical addition followed by an intramolecular electrophilic aromatic substitution can be accomplished [186, 187). Further Mn(III)-mediated anodic additions of 1,3-dicarbonyl and l-keto-3-nitroalkyl compounds to alkenes and alkynes are reported in [110, 111, 188). Sorbic acid precursors have been obtained in larger scale and high current efficiency by a Mn(III)-mediated oxidation of acetic acid acetic anhydride in the presence of butadiene [189]. Also the nitromethylation of benzene can be performed in 78% yield with Mn(III) as electrocatalyst [190]. A N03 radical, generated by oxidation of a nitrate anion, can induce the 1,4-addition of aldehydes to activated olefins. NOj abstracts a hydrogen from the aldehyde to form an acyl radical, which undergoes addition to the olefin to afford a 1,4-diketone in 34-58% yield [191]. 

The iijiechanism suggested by kinetic data involved generation of nitromethyl radicals Isy Ce +, followed by radical attack on the aromatic substrate and oxidative rearomatization. 

Manganese(iii) acetate was found to bring about aromatic substitution by a nitromethyl group when it reacted with nitromethane and an aromatic substrate in acetic acid. A nitromethyl radical intermediate has been proposed which is apparently electrophilic, since it fails to substitute into nitrobenzene. ... 

Vasella has used deoxy-nitro sugars for the synthesis of various biologically important carbohydrates,10 and the radical nitromethylation of deoxy-nitro sugars has been used for synthesis of fructose 6-phosphate11 and 6-C-methyl and 6-C-(hydroxymethyl)analogues of V-acetylneuraminic acid (see Scheme 7.2).12... 

Recently, it was reported that a nitromethyl group was reduced to the corresponding oxime by reaction with Bu3SnH in the presence of radical initiator (Eq. 7.61).68 Interestingly, primary nitro groups are selectively reduced to oximes in the reaction of the compounds containing both primary and secondary nitro groups (Eq. 7.62).69 The product of Eq. 7.60 may not be correct, but may be the oxime. 

Thermolysis of a stable radical 4-[(hydroxyimino)nitromethyl]-2,2,5,5-tetra-methyl-3-imidazolin-l-oxyl 13 gives the corresponding spin-labeled nitrile oxide. It was also identified in isoxazolines formed in cycloadditions with olefins (88). 

A primary nitromethyl group can be reduced to the corresponding oxime by a radical reaction with tin.93 The reaction is remarkably selective for primary nitro groups over secondary groups (Scheme 43).94... 

At this point a common method of conversion of tertiary aliphatic nitro compounds into nitromethyl derivatives and, further, into aldehydes deserves mention (Komblum Erickson 1981). According to this method, the reagent NaCH2N02 is used. To prepare this reagent, sodium hydride reacts with nitromethane. Then a tertiary aliphatic nitro compound is introduced into the solution formed. Several organic solvents were probed. The reaction considered proceeds most effectively in DMSO. Komblum and Erickson (1981) attributed this feature to small amounts of NaCH2SOCH3 (sodium dimsyl) produced in DMSO at the expense of its reaction with sodium hydride. Sodium dimsyl acts as a powerful one-electron reducer that induces the following chain anion radical process ... 

It has been shown that loss of a hydroxyl radical from metastable p-nitromethyl benzoate ions involves abstraction of an ortho hydrogen by the nitro group [474]. From metastable ion abundance measurements on the 3-d, and 2-dj compounds, an average isotope effect /OH//OD of 1.41 was determined. On the basis of an intermolecular isotope effect, it has been further suggested that this loss of a hydroxyl radical from the p-nitromethyl benzoate ion is also preceded by hydrogen transfer from the methyl group to the ring [474], The ratio (M— OH)+/M+ for the d3 -isomer was found to be less than half the same ratio for the unlabelled isomer. 

Halogenation of A(-methyl groups is possible under radical conditions <93ZOBI879>. Nitromethyl substituents are subject to Srn 1 substitution under photolytic stimulation, and the exocyclic nitro group can also be replaced by malonate ion, or reduced to hydrogen by tributyltin hydride <94BSF200>. 

It has been shown that loss of a hydroxyl radical from metastable p-nitromethyl benzoate ions involves abstraction of an ortho hydrogen by the nitro group [474]. From metastable ion abundance measurements on the 3-di and 2-di compounds, an average isotope effect/qh/fon... 

Free-radical aromatic nitromethylation is promoted by different cerium(IV) salts (Kurz and Ngoviwatchai, 1981). The reaction is carried out by refluxing a mixture of an aromatic compound, nitromethane, and a cerium(IV) salt in acetic acid (scheme 46). The mechanism in-... 

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