Alkylation reactions Subject

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... 

Alkylation reactions are subject to the same constraints that affect all Sn2 reactions (Section 11.3). Thus, the leaving group X in the alkylating agent R—X can be chloride, bromide, iodide, or tosylate. The alkyl group R should be primary or methyl, and preferably should be allylic or benzylic. Secondary halides react poorly, and tertiary halides don t react at all because a competing E2 elimination of HX occurs instead. Vinylic and aryl halides are also unreactive because backside approach is sterically prevented. 

In the case of ring-nitrogen atoms, A-acylation and A-alkylation reactions have been described. Thus, Scheme 16 shows that compound 115 was subjected to acetylation <1999J(P1)1067>. If the reaction is carried out with acetic anhydride in pyridine under an argon atmosphere for 15 h, the acetyl compound 117 can be obtained. The same reaction mixture, however, when left to stand for 7 days, undergoes a further acetylation step to yield the acetate 118. 

In 2002, Grubbs and co-workers reported the first CM reactions of allyl phosphines.In an initial reaction, subjecting allyl diphenylphosphine to catalyst 5 (5 mol%) failed to produce any of the desired cross-product. However, by protecting the phosphine as its borane complex, CM reactions could be achieved in good yield with high E-selectivity (Equation (5)). Notably, catalyst 5 failed to dimerize borane-protected vinyl diphenylphosphine. This result was attributed to substrate trapping of the catalyst as an unreactive Fischer carbene, a situation analogous to that observed in the CM reactions of alkyl vinyl ethers. 

Better yields of alkylbenzenes result if the arylsodium is first prepared and then subjected to a suitable alkylation reaction. In the preparative example of butylbenzene (Expt 6.1), benzylsodium is conveniently obtained by first forming phenylsodium by reaction between sodium and chlorobenzene in a toluene medium, and then heating the toluene suspension of the phenylsodium at 105 °C for about 35 minutes when a transmetalation process occurs (formulated at the beginning of Expt 6.1). 

The mechanism of allylic alkylation reactions has been the subject of significant investigation.80,113,114 The two major approaches were based on the use of a cyclic substrate and use of chiral substrates and have given rise to the model shown in Scheme 22.14. The model also includes the following general observations ... 

Very recently, the preparation of zinc /3-diiminate derivatives became the subject of interest due to their catalytic activity in the copolymerization of CO2 with epoxidesd They can be prepared in high yields by direct reaction of the corresponding /3-ditmines with diaUcylzinc compounds or by treatment of the /3-diimine-lithium salts with zinc halide followed by an alkylation reaction (Scheme 9). 

Isoxazole-supported selenium resins, produced via 1,3-dipolar cycloaddition of nitrile oxides with propargyl selenium resin, were subjected to a-alkylation reactions with various electrophiles, leading to 3-aryl-5-i4-substituted ethenylisoxazoles in satisfactory yields (62-78%) and purity (90-99%). Compound 238 gave olefin 240, through selenoxide elimination from the a-alkylation product 239 (Scheme 56) <2003OL4649>. 

Repetitive Alkylation Reaction. The tetrahydrofuran-insoluble materials, in certain instances, were subjected to a second alkylation reaction. In these cases there were three notable differences in the experimental results. First, the green color of the naphthalene radical anion and dianion persisted for a significantly longer time following the addition of the coal residue. Second, gas evolution, presumably butene-1, was detectable during the addition of butyl iodide or butyl mesylate but, significantly, not during the addition of methyl iodide. Third, the rate of formation of potassium iodide was much more rapid, such that the rate difference between butyl iodide and methyl iodide was not evident. 

A subtle substituent effect is evident in the reactions of (159 equation 66) when the amine (R = alkyl) is subjected to acid-induced rearrangement it gives the hydride migration product (160), whereas the amide (R = acyl) reacts almost exclusively by ring contraction. ... 

Many TP derivatives are subject to tautomerism. Thus substance 92 (Scheme 24) can be drawn in the form of one (vinylogous) lactim structure (92a) and three different (vinylogous) lactams (921>-d). Several tools have been used to establish the exact tautomeric structures, especially NMR, IR, and mass spectrometry. X-ray diffraction, alkylation reactions, and quantum-chemical calculations cf 01AHC(81)l). 

The use of a microflow system enables sequential alkylation reactions with two different N-acyliminium ions as alkylating agents (Scheme 8.8). The first alkylation of thiophene was carried out using a microflow system to obtain the monoalkylation product, which was directly subjected to the second alkylation with a different N-acyliminium ion to obtain the dialkylation product. In the second alkylation, the use of a microflow system is not necessary because the third alkylation seems to be very slow at -78 °C. 

The alkylation, with the more reactive of alkyl halides, of the sodium salts of monoes-terified phosphonothioic acids (equation 22) (see also Scheme 11) or of the disodium salts 107 results in preferential S-alkylation, and the same situation obtains for the salts of phosphinothioic acid " methylation can also be carried out with dimethyl sulphate. Alkylations may also be performed under phase-transfer conditions. From both practical and theoretical perspectives, the subject is more complex, since the course of alkylation reactions depends on the nature of the alkylating agent, on the polarity of solvent and whether this is protic or non-protic and on the concentrations of reactants a study of these features has been the subject of two reports In non-polar or weakly polar aprotic media, or in EtOH, alkylation occurs almost exclusively on sulphur, but in dipolar aprotic solvents, O-alkylation also takes place. The relative yields of sulphur- and oxygen-substituted derivatives, [Qs/Qol depends, for a given solvent, on the nature of substituents on phosphorus, i.e. essentially, whether the substrate is a thiophosphoric, thiophosphonic or thiophosphinic acid. With alkyl tosylates as alkylating agents at 0.02 m in hmpt, the alkylation of sodium 0,0-dialkyl or diphenyl phosphorothioates results in 100% overall conversions with [Qs/Qo] 5 the overall yields for sodium diphenyl- or diisopropyl-phosphinothioates are lower (50-100%) with [Qs/Qo] 1 ... 

Coke formation [911-915] is a very important phenomenon in most hydrocarbon conversions on zeolites. Also, reactions of olefins on zeolites (in particular isomerization and oligomerization) were frequently subject of in-situ IR experiments [916-919] and theoretical treatment [740, 920], in many cases because of the close relation to coke formation, for instance, during isomerization and alkylation reactions [835,916,917]. Further examples are presented in... 

The novice reader may think that the subject is an emerging field however, the green chemistry name is an umbrella for many well-established ideas and techniques that already exist in the literature. None of the techniques under the green technology label can therefore be considered new. For example, the first room-temperature ionic liquid, ethylammonium nitrate [EtNH3] [N03] , which melts at 12°C was discovered by Paul Walden in 1914 [40], Ionic liquids were also observed in Friedel-Crafts acylation and alkylation reactions [41,42], The reader is directed to two reviews that chronicle the historical development of ionic liquids [43,44]. Microwave-assisted synthesis was developed by Gedeye and Westaway at Laurentian University in Sudbury, Canada [45-48],... 

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