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Pyridines, nucleophilic additions onto

The pffa of 3-methylpyridine, whose anion cannot be delocalized onto N, is closer to that of toluene, and deprotonation gives only low yields with most bases. However, with a combination of BuLi and lithiodimethylaminoethanol (LiDMAE) deprotonation is quantitative but yields products 561 arising from apparent lithiation a to N (Scheme 224) Trying to force lateral lithiation of pyridines is generally doomed to failure, as ring lithiation or nucleophilic addition nsnally takes place first . [Pg.615]

Fort and coworkers have reported the use of BuLi-(S)-N-methyl-2-pyrroUd-ine methoxide 10 for the chemo, regio- and enantioselective reaction of pyridine derivatives with aldehydes [22] (Scheme 3) in this chemistry the amine alkoxide plays a dual role in first preventing classical nucleophilic addition of BuLi onto the heteroaromatic ring, and secondly mediating the enantioselective addition. [Pg.4]

Being anionic carbonyl synthons, the nitroalkanes have been explored extensively for their conversion into the corresponding carbonyl compounds. For example, the embedment of a nitroalkane onto an activated basic silica gel or the blockage of the C-protonation of nitronate with a protonated concave pyridine. The reaction under the latter condition is called the soft Nef reaction. In addition, the introduction of a y-trimethylsilyl group is proved to smooth the Nef reaction. Moreover, when a primary nitroalkane is treated with nitrite/acetic acid, a carboxylic acid is resolved. Furthermore, the oxidative Nef reaction has successfully converted the nitro cyclohexadienes into the substituted phenols via a nucleophilic addition. [Pg.2026]

Scheme 1-137. Nucleophilic addition of -butyllithium onto 3-(trifluoromethyl)pyridine and subsequent lithium fluoride elimination. Scheme 1-137. Nucleophilic addition of -butyllithium onto 3-(trifluoromethyl)pyridine and subsequent lithium fluoride elimination.
Pyridine can be attacked by nucleophiles at the C2/C6 and C4 positions in a manner analogous to the addition of nucleophiles to a carbonyl group in a 1,2 or 1,4 fashion. Attack at the C3/C5 positions is not favoured because the negative charge on the intermediate cannot be delocalised onto the electronegative nitrogen atom. [Pg.40]

As mentioned before, alkyl radicals and acyl radicals have a nucleophilic character therefore, radical alkylation and acylation of aromatics shows the opposite reactivity and selectivity to polar alkylation and acylation with the Friedel-Crafts reaction. Thus, alkyl radicals and acyl radicals do not react with anisole, but may react with pyridine. Eq. 5.1 shows the reaction of an alkyl radical with y-picoline (1). The nucleophilic alkyl radical reacts at the 2-position of y-picoline (1), where electron density is lower than that of the 3-position. So, 2-alkyl-4-methylpyridine (2) is obtained with complete regioselectivity. When pyridine is used instead of y-picoline, a mixture of 2-alkylpyridine and 4-alkylpyridine is obtained. Generally, radical alkylation or radical acylation onto aromatics is not a radical chain reaction, since it is just a substitution reaction of a hydrogen atom of aromatics by an alkyl radical or an acyl radical through the addition-elimination reaction. Therefore, the intermediate adduct radical (a complex) must be rearomatized to form a product and a hydrogen atom (or H+ and e ). Thus, this type of reactions proceeds effectively under oxidative conditions [1-6]. [Pg.157]


See other pages where Pyridines, nucleophilic additions onto is mentioned: [Pg.95]    [Pg.308]    [Pg.602]    [Pg.206]    [Pg.207]    [Pg.207]    [Pg.311]    [Pg.534]    [Pg.97]    [Pg.168]    [Pg.154]    [Pg.341]    [Pg.81]    [Pg.491]    [Pg.111]    [Pg.414]   
See also in sourсe #XX -- [ Pg.95 ]




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Pyridines addition

Pyridines nucleophilic

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