Alkylation at carbon

Allyl halides do however give us good yields of alkylation at carbon ... 

The anion of a p keto ester may be alkylated at carbon with an alkyl halide and the product of this reaction subjected to ester hydrolysis and decarboxylation to give a ketone... 

Although the addition of carbon monoxide to a carbonium ion R+ leads to a product R—C =0, with a new carbon-carbon bond, one may raise the question whether this oecurs by direct alkylation at carbon ... 

Alkylation at carbon positions activated by electron-withdrawing groups is illustrated by the spiroannelation of cyclopentanone and cyclohexanone by sonication of the parent compound with potassium t-butoxide and 1,4-dibromobutane (Eq. 3.22). The so-nochemical improvement is especially large with cyclopentanone which is normally particularly prone to self-condensation [119]. 

Both reactions act to reduce hydrogen bonding within the coal structure which may have a direct positive impact on liquefaction reactivity. More indirectly, these reactions lower the concentration of OH species in coal-derived products and hence, reduce the extent of retrogressive condensation via ether bridge formation. Reducing production of THF-insoluble condensation products increases the net THF-soluble coal conversion observed during the liquefaction experiment. None of the spectra from coals pretreated with alkyl alcohols and HCl showed any significant evidence of alkylation at carbon sites in the coal. 

As a result, these anions can gain exceptional stability and their carbon acids are unusually acidic. Because the above resonance forms probably play very important roles in stabilizing the anion, these species are not purely carbanions. However, thermodynamics favors reactions (protonation or alkylation) at carbon so their behavior is generally characteristic of carbanions. It also should be noted that kinetics often favor reaction at the heteroatom in these anions though leading to the less stable product. ... 

The enoiate is alkylated at carbon with methyl iodide. 

Unsubstituted aliphatic alcohols cannot usually be a-metalated by treatment with strong bases (to yield a dianion). Dilithiated methanol has been prepared by treatment of Bu3SnCH2OH with two equivalents of BuLi, and can be alkylated at carbon [287]. Treatment of allyl alcohol with excess BuLi/TMEDA in pentane at room temperature does not lead to formation of the dianion of allyl alcohol but to addition of BuLi to the C-C double bond [288] (Scheme 5.33). Benzylic alcohols, on the other hand, can be deprotonated twice and, depending on the substitution pattern at the... 

Chapter 5 dealt with chemoselectivity how to react one functional group rather than another. Now we must face a more subtle and demanding problem how to react one specific part of a single functional group and no other. This is regioselectivity. We have already seen that anions of phenols 2 are alkylated at oxygen to give ethers 3 while enolate anions 5 are alkylated at carbon to form a new C-C bond 6. 

While the ability of enamines to be alkylated at carbon is their synthetically most useful attribute, the oxidation-reduction chemistry of such systems is also well documented. 

Alkylation at carbon, problems with enamines Application to the synthesis oflipoic acid Alkylation with tertiary alkyl groups Acylation at Carbon... 

Lithio-indoles are equally useful again, the position of attack depends on both solvent and the nature of the electrophile. It is important to note that when an iV-metallated 3-substituted indole alkylates at carbon, necessarily a 3,3-disubstituted-3//-indole is formed, which cannot re-aromatise to form an indole (see 20.1.1.6 for rearrangements of 3,3-disubstituted indolenines). 

The direct N-alkylation of 4,5-diphenyl-1,2,3-triazoIe produces mixtures, but it is possible to obtain fair yields of the 1-alkyl isomer using the silver or thallium salt (Eq. 15). " Alkylation at carbon has been reported and produces surprisingly good yields (Eq. 16). 

Enamines normally react with methyl iodide to give two products one arising from alkylation at nitrogen and the second arising from alkylation at carbon. For example,... 

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