Alkylation reactions general features

One of the general features of the reactivity of enolate anions is the sensitivity of both the reaction rate and the ratio of C- versus O-alkylation to the degree of aggregation of the enolate. For example, addition of HMPA fiequently increases the rate of enolate alkylation... 

The most active samples for n-C4 isomerization, (NH4)2.4P and Csi.gP, showed opposite reactivities in liquid alkylation. The first one gave rise to a high production of TMP while the second one was only initially slightly active. The main difference between these two samples concerned their porosity (NH4)2.4P was mesoporous while Csi.gP was mainly microporous. Then, one may suggest that the presence of mesoporosity is essential for the accessibility of the reactants to the acid sites and the desorption of the products. As a consequence the catalytic activity seems more governed by the textural features than by the acidity. As a general trend, the samples which were, at the same time, active and stable for the alkylation reaction, exhibited a mesoporosity equivalent to about 40 m. g-i. 

Vinyl halides (example 17, Table VII) were first observed by Kroper to form acrylic esters by reaction with carbon monoxide under pressure and tetracarbonylnickel in methanol at 100°C. These reactions were later shown to occur under much milder conditions. Highly stereospecific reactions were observed c/s-vinyl halides gave cis-carbonylation products and trans-vinyl halides trans-carbonylation products (example 18, Table VII). Retention of configuration of alkyl substrates in carbonylation seems to be a general feature in carbon monoxide chemistry (193a). 

The synthesis of commercial nonylphenols generally proceeds through an alkylation reaction of phenols with propylene trimer [124], which itself has a spread of isomers [47]. The alkylation occurs preferentially at the para position of the phenol, but 3-6% of ortho-nonylphenol can be found in commercial products [125]. Also meta and disubstituted species have been mentioned [47]. A common feature of the isomers appears to be a dimethyl substitution of the a-carbon atom [83]. 

The general feature of alkylation reactions at a carbon atom is that they can be achieved under sonication using solid bases even in apolar solvents. The advantage is that side reactions are generally minimised. Deprotonation occurs readily on a benzylic position in the presence of aqueous sodium hydroxide, as shown with indene (Eq. 3.21) [117]. A quantitative yield of the alkylated product can be obtained using sonication in the presence of a PTC. It was suggested that alkylation of cyclopentadiene or indene by secondary or tertiary alkyl halides in the presence of potassium hydroxide and Ali-quat occurred via a SET process [118]. 

While most of the work has been done commencing with the nickel(II) complex (51), the chemistry is quite general. The enamine complex (53) can be deprotonated on nitrogen to yield the neutral imine complex (55). Even the protons of the methyl group in the enol ether complex (52) are sufficiently acidic for the formation of the neutral complex (54). Both of these reactivity features occur together in the alkylation reaction shown in Scheme 18.126 The macrocyclic rings in complexes such as (52), (53) and especially the more flexible complex (56) are not planar but bowl-... 

We include in Sections I,A and I,B some general features of the Tsuji-Trost reaction with comments on kinetic versus thermodynamic control in allylations and in alkylations in general. Then we review in Sections II, III, and IV all cases known to the authors of the application of the Tsuji-Trost reaction to ambident nucleophilic aromatic heterocycles. This leaves out of the review the allylation of such heterocyclic ambident nucleophiles as 2-piperidone and the like. By aromatic, we mean any heterocycle for which a tautomeric or mesomeric formula can be written that is aromatic in the normal structural sense of having 4n + 2n- electrons cyclically conjugated. 

The alkylation of C3, C4 and C5 olefins with isobutane in sulfuric acid is a large scale commercial process. The reaction has been extensively studied and its general features are well understood and documented in several lucid reviews (1-3). 

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