Nitromethyl anions

Electrochemical oxidation of 2,3,4,5-tetraphenylpyrrole in aqueous media yields 3,3,4,5-tetraphenylpyrrolin-2-one, whereas when the oxidation is conducted in nitromethane, nucleophilic attack by the nitromethyl anion and subsequent rearrangement of the adduct with the extrusion of the nitrite ion lead to the formation of 2,3,4,6-tetraphenylpyridine (B-77MI30507, 81H(15)495>. 

A Bronsted j5b value of 0.5 and acn value of 1.31 have been calculated for deprotonation reactions of (3,5-dinitrophenyl)nitromethane promoted by substituted benzoate ions and of substituted (3-nitro-, 4-nitro- and 3,5-dinitro-)phenylnitro-methanes promoted by benzoate ion, respectively, in methanol. " The intrinsic rate constants are (2.0-6.3)xl0" times lower than for the same reactions in acetonitrile solution, and this has been attributed to commensurate reduction of strength of the hydrogen bond between the carbon acid and benzoate ion in the imbalanced transition state. The transfer activity coefficient (log y ) from methanol to acetonitrile solution have been calculated for (m-nitrophenyl)nitromethyl anion (3.6) and (/w-nitrophenyl)-nitromethane (—1.0). 

The formation of nitroalkyl glycosides, illustrated in Figure 7.12, is limited in scope and few examples have been reported. The problems associated with this reaction involve the acidity of nitromethyl groups. Specifically, after formation of the C-glycoside, nitromethyl anions are easily formed. Moreover, when acetyl protecting groups are used, nitronates readily form. The few examples illustrated in this section are intended to convey the relatively limited accessibility of these compounds. 

Calculations revealed two variants of the structural types in which the necessary conditions are satisfied for the electron transfer in the first step [Eq. (9.5a)]. In the first of these, nitromethyl anion II approaches in its stable planar form (starting from 3-3.5 A) chloronitromethane in a head-to-head fashion. An even more positive overlapping of the frontier orbitals of the electron acceptor and electron donor (nitromethyl anion) is achieved if the latter undergoes certain structural transformations, namely, the rotation about the C—N bond and pyramidalization of the carbon atom (III) ... 

Although the nitro group plays a crucial role in most of these SrnI reactions, reactions of this type have synthetic application beyond the area of nitro compounds. The nitromethyl groups can be converted to other functional groups, including aldehydes and carboxylic acids.Nitro groups at tertiary positions can be reductively removed by reaction with the methanethiol anion.This reaction also appears to be of the electron-transfer type, with the methanethiolate anion acting as the electron donor ... 

Nickel(II) complexes of type (599) unsaturated 14-membered tetrazamacrocycles react with the anion of nitromethane under basic conditions to give the 5-nitromethyl derivatives (600), and the square planar diperchlorates (601) upon treatment with HC104 (Equation (19)) 151... 

The anion of nitromethane is particularly reactive in S l reactions. Various kinds of tertiary nitro groups are replaced by a nitromethyl group on treatment with the anion of nitromethane (Section 7.1).49 2-Iodoadamantane reacts with the anion of nitromethane in the presence of acetone enolate (entrainment reaction) under irradiation of a 400-W UV lamp to give 2-ni-tromethyladamantane in 68% yield, (see Eq. 5.32).50a 1-Iodoadamantane also reacts with the anion of nitromethane in a similar way.50b... 

The reaction of tertiary nitro compounds with the sodium salt of nitromethane followed by the Nef reaction provides a good method forthe preparation of quaternary aldehydes (Eq. 7.10).8 Because the nitromethyl group can be transformed into other groups such as CN, C02H, or CH2NH2, the SRN I reaction of tertiary nitro compounds with the anion of nitromethane is a synthetically useful method (Kornblum reaction).10 For example, the nitromethylation of tertiary nitro compounds has been applied for preparing starting materials for cascade polymers (Eq. 7.11).9... 

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 is important to note that the absence of transfer effects on these reactions does not imply the total absence of transfer effects. Solubility measurements on DMD show that yD1ID = 1T7. It also seems possible that values of Y close to unity are more especially associated with reactions in which the substrate is electrically neutral and the transition state is a mono-cation. The analysis of acid dissociation of acetic acid in H20-D20 mixtures (Gold and Lowe, 1968 see Section VBl) and the study of proton transfer to nitromethyl and nitroethyl anions (Goodall and Long, 1968) suggest that transfer effects are much more significant for equilibria (or pseudo-equilibria for the formation of a transition state) in which a neutralization of electric charge occurs. 

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]. 

Nitroarenes can be nitromethylated through reaction with the nitromethane anion followed by oxidation of the initial product... 

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