Benzylic nitro anions

The SrnI reaction also proceeds with tertiary benzyl nitro compounds lacking a p-nitro substituent. The nitro group at the benzyl position acts as the electron acceptor, and decomposes to the benzyl radical and nitrite anion. The nitronate anion nucleophiles are then alkylated. Entry 5 in Scheme 12.7 provides a specific example. 

This reaction also can be made to proceed with tertiary benzyl nitro compounds lacking the p-nitro substituent. The nitro substituent at the benzyl position provides sufficient stabilization to permit the electron transfer to proceed, generating the radical anion. This species decomposes to a tertiary benzyl radical by loss of nitrite ion. Substituted nitrocumyl systems can alkylate nitronate anions in HMPA sol-... 

A mechanism of this type permits substitution of certain aromatic and ahphatic nitro compounds by a variety of nucleophiles. These reactions were discovered as the result of efforts to explain the mechanistic basis for high-yield carbon alkylation of the 2-nitropropane anion by p-nitrobenzyl chloride. p-Nitrobenzyl bromide and iodide and benzyl halides that do not contain a nitro substituent give mainly the unstable oxygen alkylation product with this ambident anion ... 

The absolute rate of dissociation of the radical anion of /i-nitrobenzyl chloride has been measured as 4 x 10 s . The w-nitro isomer does not undergo a corresponding reaction. This is because the meta nitro group provides no resonance stabilization of the benzylic radical. 

Ono and Kamimura have found a very simple method for the stereo-control of the Michael addition of thiols, selenols, or alcohols. The Michael addition of thiolate anions to nitroalkenes followed by protonation at -78 °C gives anti-(J-nitro sulfides (Eq. 4.8).11 This procedure can be extended to the preparation of a/jti-(3-nitro selenides (Eq. 4.9)12 and a/jti-(3-nitro ethers (Eq. 4.10).13 The addition products of benzyl alcohol are converted into P-amino alcohols with the retention of the configuration, which is a useful method for anri-P-amino alcohols. This is an alternative method of stereoselective nitro-aldol reactions (Section 3.3). The anti selectivity of these reactions is explained on the basis of stereoselective protonation to nitronate anion intermediates. The high stereoselectivity requires heteroatom substituents on the P-position of the nitro group. The computational calculation exhibits that the heteroatom covers one site of the plane of the nitronate anion.14... 

Recently, Behiman and coworkers discussed the mechanism of the Elbs oxidation reaction and explained why the para product predominates over the ortho product in this oxidation. According to the authors, semiempirical calculations show that the intermediate formed by the reaction between peroxydisulfate anion and the phenolate ion is the species resulting from reaction of the tautomeric carbanion of the latter rather than by the one resulting from the attack by the oxyanion. This is confirmed by the synthesis of the latter intermediate by the reaction between Caro s acid dianion and some nitro-substituted fluorobenzenes. An example of oxidative functionalization of an aromatic compound is the conversion of alkylated aromatic compound 17 to benzyl alcohols 20. The initial step in the mechanism of this reaction is the formation of a radical cation 18, which subsequently undergoes deprotonation. The fate of the resulting benzylic radical 19 depends on the conditions and additives. In aqueous solution, for example, further oxidation and trapping of the cationic intermediate by water lead to the formation of the benzyl alcohols 20 (equation 13) . ... 

This cyclopropanation can be extended to anions of ally lie, benzylic, and tertiary nitro compounds. 

Grignard reagent.80 Competition by nucleophilic aromatic substitution was not observed unless the only active position(s) was (were) substituted with a leaving group, as in the reaction of l-methoxy-2-nitro-naphthalene which gave 1 -alkyl-2-nitronaphthalenes in 73-95% yields.81 The use of Me3SiCH2MgCl (Peterson reagent) provides an entry to nitro-substituted benzyl anion intermediates, as shown in the example of Scheme 9.82... 

While interacting with the anion of 2-nitropropane, benzyl chloride and its derivatives bearing groups CN, CF3, Me2N+, Me, and Br in the para position yield products of O-alkylation (route a in Scheme 4-11). Meanwhile, when the nitro group occupies the para position instead of these substituents, the reaction gives the products of C-alkylation (route... 

We get the full value when there are no nitro groups to take the brunt of the negative charge. This vinylic substitution (an unusual reaction ) has a p value of +9.0. It cannot be an S>j2 reaction or it would have a small p value and it cannot be an S>j 1 reaction or it would have a negative p value (fewer electrons in the transition state). It must be an addition-elimination mechanism through a benzylic anion delocalized round both benzene rings. 

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