Nitro Carbanions

Substances that form carbanions, such as nitro compounds, hydrocyanic acid, malonic acid, or acetylacetone, react with vinyl ethers in the presence of water, replacing the alkyl group under mild conditions (245). 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

A variety of ring syntheses have been devized which depend on carbanion addition to an activated double bond. The examples depicted in Scheme 74 illustrate the use of inter alia cyano and nitro groups which are subsequently eliminated. In appropriate instances the inclusion of additional eliminable groups ensures the formation of fully aromatized products. 

Enolates of aldehydes, ketones, and esters and the carbanions of nitriles and nitro compounds, as well as phosphorus- and sulfur-stabilized carbanions and ylides, undergo the reaction. The synthetic applications of this group of reactions will be discussed in detail in Chapter 2 of Part B. In this section, we will discuss the fundamental mechanistic aspects of the reaction of ketone enolates with aldehydes md ketones. 

A great number of N-substituted 4-hydroxy-3-nitro-l,8-naphthyridin-2 (IH)-ones are obtained by reaction of N-substituted azaisatoic anhydrides with ethyl nitroacetate carbanion (Section II,A,4,a). A very specific method, more recently developed, is that of the inverse Diels-Alder method, involving the reactions of enamines with 5-nitropyrimidine (Section II,A,4,b). 

The p-chloro analog of phentermine has much the same activity as the parent compound, with perhaps a somewhat decreased activity on the central nervous system. Alkylation of p-chloro-benzyl chloride with the carbanion obtained from treatment of 2-nitropropane with strong base affords the compound containing the required carbon skeleton (74). Catalytic reduction of the nitro group yields chlorphentermine (75). ... 

The ability of a nltro group in the substrate to bring about electron-transfer free radical chain nucleophilic subsdnidon fSpj li at a saniratedcarbon atom is well documented. Such electron transfer reacdons are one of the characterisdc feanires of nltro compounds. Komblum and Russell have established ihe Spj l reaction independently the details of the early history have been well reviewed by them. The reacdon of -nitrobenzyl chloride v/ith a salt of nitro ilkane is in sharp contrast to the general behavior of the ilkyladon of the carbanions derived from nitro ilkanes here, carbon ilkyladon is predominant. The carbon ilkyladon process proceeds via a chain reacdon involving anion radicals and free radicals, as shovmin Eq. 5.24 and Scheme 5.4 fSpj l reacdoni. 

Carbanions of ct-chloroalkyl phenyl sulfones react with nitrobenzenes to effect tlirect nucleophilic replacement of hydrogens located on o and para to the nitro group fEq. 9.24. A very important feature is that VNS of hydrogen usually proceeds faster than conventional SnAt of halogen located In equally activated positions fEq. 9.25. The rule that VNS of... 

The nucleophilic substitution of the nitro group in nitro-arene complexes works almost as well as that of Cl" and such substitutions were achieved by Chowdhurry et al. with O, S, and N nucleophiles and with stabilized carbanions [97,98] Eq. (28) and Table 8. 

Nitro Anions Remov of a proton from an aliphatic nitro compound gives a carbanion (R2C-NO2) that can be alkylated at oxygen or carbon. ... 

The mechanism of these reactions is usually Sn2 with inversion taking place at a chiral RX, though there is strong evidence that an SET mechanism is involved in certain cases, ° especially where the nucleophile is an a-nitro carbanion and/or the substrate contains a nitro or cyano group. Tertiary alkyl groups can be introduced by an SnI mechanism if the ZCH2Z compound (not the enolate ion) is treated with a tertiary carbocation generated in situ from an alcohol or alkyl halide and BF3 or AlCla, or with a tertiary alkyl perchlorate. ... 

The latter reagent also methylates certain heterocyclic compounds (e.g., quinoline) and certain fused aromatic compounds (e.g., anthracene, phenanthrene). The reactions with the sulfur carbanions are especially useful, since none of these substrates can be methylated by the Friedel-Crafts procedure (11-12). It has been reported that aromatic nitro compounds can also be alkylated, not only with methyl but with other alkyl and substituted alkyl groups as well, in ortho and para positions, by treatment with an alkyllithium compound (or, with lower yields, a Grignard reagent), followed by an oxidizing agent such as Bra or DDQ (P- 1511). 

A different kind of alkylation of nitro compounds uses carbanion nucleophiles that have a chlorine at the carbanionic carbon. The following process takes place ... 

Nitro-, 4-nitro-, 7-nitro-, 5,7-dinitro-, and 6,8-dinitroquinoline react with the carbanion of chloromethyl phenyl sulfone to give products of substitution of hydrogen at positions 4 3 8 6,8 and 5,7 respectively <96LA641>. The base-induced reaction of benzoyl chloride salts of quinoline iV-oxides with carbonitriles to give 2-quinolyldiacylamines as the main products has been reported <96TL(37)69>. 

---