C-Monoalkylation

Nitration of triazole and its C-monoalkyl derivatives fails. Aryltriazoles are nitrated on the aryl ring in preference to the triazole, but 3-p-nitrophenyltriazole in which each ring is deactivated gives l-nitro-3-j7-nitrophenyltriazole which rearranges at 120°C to 3-nitro-5-p-nitrophenyltriazole <72CC37>. 

The guanidine 1 can be alkylated more readily than 2, but nevertheless is a very effective proton acceptor. It is preferred to DBU as the base for esterification of carboxylic acids by an alkyl halide. Thus severely hindered tertiary carboxylic acids can be alkylated by isopropyl iodide in about 90% yield in the presence of 1 (1.5 equiv.). Selective C-monoalkylation of a typical /J-keto ester was effected in 80% yield in the presence of I (1.0 equiv.). Preliminary experiments suggest that 1 is not particularly useful for base-promoted elimination reactions, but that the more hindered 2 is superior to collidine or DBN for this purpose. 

In the first instance, excess a- or y-picoline is treated at low temperatures with sodium amide and an alkyl halide. The yields of C-monoalkyl-pyridines are lowered by alkylation at the nitrogen atoms, dehydrohalo-genation of the alkylating agent, and further alkylation of the product at the site of the remaining active hydrogens. ... 

C-monoalkylated products are formed with ZSM-5 zeolites. With ALPO-11, SAPO-11 or MAPSO-11, no enhancement of C- monoalkylated products was noticed, however, N,C-dialkylated products are observed which are formed by the isomerization of N,N-dialkylated compounds. 

C-Alkylation. This chelated -diketone reacts with primary alkyl halides in DMF to give mainly C-monoalkylation products. C-Dialkylation products are obtained in addition from alkylation with benzylic or allylic halides. O-Alkylation has not been observed. 

Whereas pyrroles are resistant to nucleophilic addition and substitution, they are very susceptible to attack by electrophilic reagents and react almost exclusively by substitution. Pyrrole itself, N- and C-monoalkyl and to a lesser extent C, C -dialkylpyrroles, are polymerised by strong acids so that many of the electrophilic... 

Enolates of carbonyl compounds are ambident anions. Although the negative charge resides predominantly at the oxygen, reactions of enolates with electrophiles can take place at the carbon terminus. C-Monoalkylation of enolates is usually accompanied by di- and polyalkylation owing to a rapid... 

C-Monoalkylation of enolizable / -dicarbonyl compounds has been achieved in hi yield by using tetraethylammonium fluoride as powerful H-bond electron donor Grignard-like syntheses with organo-boranes, which had failed previously, have now been reported, yielding trans-2l y ic alcohols from aldehydes... 

In a polluted or urban atmosphere, O formation by the CH oxidation mechanism is overshadowed by the oxidation of other VOCs. Seed OH can be produced from reactions 4 and 5, but the photodisassociation of carbonyls and nitrous acid [7782-77-6] HNO2, (formed from the reaction of OH + NO and other reactions) are also important sources of OH ia polluted environments. An imperfect, but useful, measure of the rate of O formation by VOC oxidation is the rate of the initial OH-VOC reaction, shown ia Table 4 relative to the OH-CH rate for some commonly occurring VOCs. Also given are the median VOC concentrations. Shown for comparison are the relative reaction rates for two VOC species that are emitted by vegetation isoprene and a-piuene. In general, internally bonded olefins are the most reactive, followed ia decreasiag order by terminally bonded olefins, multi alkyl aromatics, monoalkyl aromatics, C and higher paraffins, C2—C paraffins, benzene, acetylene, and ethane. 

Studies of reaction mechanisms ia O-enriched water show the foUowiag cleavage of dialkyl sulfates is primarily at the C—O bond under alkaline and acid conditions, and monoalkyl sulfates cleave at the C—O bond under alkaline conditions and at the S—O bond under acid conditions (45,54). An optically active half ester (j -butyl sulfate [3004-76-0]) hydroly2es at 100°C with iaversion under alkaline conditions and with retention plus some racemization under acid conditions (55). Effects of solvent and substituted stmcture have been studied, with moist dioxane giving marked rate enhancement (44,56,57). Hydrolysis of monophenyl sulfate [4074-56-0] has been similarly examined (58). 

Olefins. EDA reacts with isobutjiene [115-11 -7] over a borosiUcate 2eohte containing 3.2% Cr at 300°C to give the monoalkylation product... 

Alkylations of enamines of a,)9-unsaturated ketones with alkyl halides often give very poor yields of C-alkylated products because of competing. -alkylation.In the type of transformation illustrated here, direct alkylations of enamines are completely unsuccessful, even in cases where hindered enamines are used. On the other hand, the metaUoenamine method can be applied generally with good success in the problem of monoalkylation of ,)3-unsaturated ketones. ... 

Enamines are readily alkylated by olefins activated by electron-withdrawing substituents. N Alkylation by one of these olefins is reversible, whereas C alkylation is not, so that a good yield of monoalkylated product is the rule. 

It is noteworthy that only in the case of dehydroquinolizidine derivatives does monomethylation produce the N-alkylated product. The formation of dialkylated products can be explained by a disproportionation reaction of the monoalkylated immonium salt caused by either the basicity of the starting enamine or some base added to the reaction mixture (most often potassium carbonate) and subsequent alkylation of the monoalkylated enamine. Reinecke and Kray 113) try to explain the different behavior of zJ -dehydroquinolizidine and zJ -dehydroquinolizidine derivatives by the difference in energies of N- and C-alkylation transition states because of the presence of I strain. 

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