Selectivity alkylation

Allyl bromide, AI2O3, days. These conditions were developed to alkylate selectively an alcohol in the presence of an amide. ... 

Intramolecular alkylation of enolates can be used to synthesize bi- and tricyclic compounds. Identify all the bonds in the following compounds that could be formed by intramolecular enolate alkylation. Select the one that you think is most likely to succeed and suggest reasonable reactants and reaction conditions for cyclization. 

Protection of the nitrogen in 4 faced the classical N- versus O-alkylation selectivity issue, which was solved by selection of the solvent system. The original protecting group, pMB, was replaced with 9-anthrylmethyl (ANM), which provided the best enantioselectivity with the newly discovered asymmetric addition to the ketimine. 

Hydrobromic acid is used in the preparation of inorganic bromide salts. The acid also is used for many organic syntheses, including alkyl bromides from alcohols or olefins, and bromophenols from phenols. The compound also is used as an acid catalyst in many alkylation, selective oxidation, isomerization, and dehydrogenation reactions. Other apphcations are in extraction of minerals and use as a reducing agent. 

A new perspective for safe and highly selective mono-N-and mono-C-alkylations Selective Mono-Methylation of Arylacetoni-triles and Methyl Arylacetates by Dimethylcarbonate... 

In the case of the asymmetric syntheses of conformationally much more flexible aldehydes and acyclic ketones applying the SAMP-method, the control of both metalation and alkylation selectivity is necessary to reach an excellent overall stereoselectivity. A variety of acyclic ketones can be prepared via the related SAMP-hydrazones in good chemical yields and routinely with overall enantioselectivities of 94-99.5% e.e. 

Thus, even in this flexible acyclic back-bone case, the electrophilic substitution occurs with almost complete asymmetric induction, which means that both deprotonation selectivity and alkylation selectivity are almost 100%. 

Methyl (2E,4E)Senoates. The dianion (2) of 1 can be prepared by treatment with I.DA and then sec-butyllithium in THF at —78°. The dianion is alkylated selectively at the a-allylic position to give 3 as the major product. Treatment of 3 with LDA induces a [2,3]sigmatropic rearrangement to 4. Remaining steps to the diunsaturated ester (6) are methylation, oxidation, and dchydrosulfcnylation.1... 

The acid is converted with thionyl chloride into the corresponding acid chloride, which reacts in a second step with the anion of the Lvans oxazolidinone 3714 to give an /V-acyloxazolidinone. This is then deprotonated with sodium hexamethyldisilazide and subsequently alkylated selectively with methyl iodide to produce compound 8. 

The isobutane-1 -butene alkylation was studied in dense CO2 in both fixed-bed and slurry reactors.165-167 Both Nafion SAC-13 and Nation SAC-25 exhibited steady-state conversions and selectivities for 50 h. Enhanced Cg alkylate selectivity could be achieved at near total butene conversion. The maximum value attained, however, was only about 40%. The higher effective alkylation rate constant for SAC-25 compared to SAC-13 indicates improved accessibility of the acid sites. Nafion SAC-13 and SAC-25 applied in a study to test the effect of supercritical fluids on alkylation exhibited only modest activities.168... 

Anthranilic acid derivatives are also rather poor nucleophiles. Unsubstituted anthranilic acid can be N-alkylated selectively with some electrophiles under basic reaction conditions without the formation of esters by O-alkylation (Scheme 6.9) [40], Even use of excess alkylating agent still gives reasonable yields of monoalkylated derivatives this indicates that the second N-alkylation is significantly slower than... 

The alkylation of 2-pyridone was effected under mild conditions by use of cesium fluoride. Benzyl and allyl chlorides furnished the A-alkylated product selectively, while secondary alkyl iodides gave O-alkylation selectively <95SL845>. 

Further, Taylor and co-workers carried out reactions to attach a suitable side chain at nitrogen, which subsequently could be cyclized to give aza analogues of ft-lactam antibiotics. Thus, the readily available inner salt 1,1-disubsti-tuted-3-oxo-l,2-diazetidinium tosylate 209 was selectively reduced at the side chain attached to N-l of 210 by sodium borohydride, or was alkylated selectively at the side chain by the reaction of 210 with a Grignard reagent (Scheme 30) <1984JOC4415>. 

A second type of methionine modification is alkylation by haloalkyl-amides (see Figure 5d). Since the sulfur atom remains unprotonated in rather strongly acidic solutions (such as pH 2), methionine usually can be alkylated selectively at pH values below 4. 

Most of the tetradentate ligands have been synthesized starting from bidentate sulfur ligand precursors. Here, the principal problem was to find a practicable method to alkylate selectively one of two identical sulfur functions. For example, it is impossible to connect intermolecularly two 1,2-benzene-dithiolate units by alkylation in order to obtain a tetradentate ligand. The intramolecular alkylation always prevails according to Eq. 2. 

The benzene sulfonyl group is used as a transfer of activation reagent to alkylate selectively the N-H of both 7//-pyrrolo[2,3-fl pyrimidines 174 and 5-aminoindole substituted on thienopyrimidines 175 (Equations 31 and 32). A variety of primary and secondary alcohols are utilized as alkylating substrates <1998TL5685>. 

The routine use of the additives has followed pilot plant and commercial studies which Indicate Improved alkylation selectivity under well mixed or poorly mixed conditions and a simultaneous reduction In acid consuming side reactions. Typical data from these tests will also be presented. 

The utility of cationic surfactants in increasing hydride transfer would be expected to be shown by an Increased yield of octanes during butene alkylation. This follows if alkylate selectivity is decided by the ratio of the rate at which intermediate Ions are captured by hydride transfer to the rate at which they add to olefins and polymerize, and If the effect of the additives Is to selectively raise the specific rate constant for hydride transfer, kg". 

Figure 18. Alkylation selectivity improved with refinery olefins...

Propargylic sulfides " and selenides have been metallated with n-butyllithium and lithium amide respectively, and allylated or alkylated selectively at the propargylic position (Scheme 34) with primary and secondary alkyl halides. - ... 

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