Olefin alkylation

The most famous mechanism, namely Cossets mechanism, in which the alkene inserts itself directly into the metal-carbon bond (Eq. 5), has been proposed, based on the kinetic study [134-136], This mechanism involves the intermediacy of ethylene coordinated to a metal-alkyl center and the following insertion of ethylene into the metal-carbon bond via a four-centered transition state. The olefin coordination to such a catalytically active metal center in this intermediate must be weak so that the olefin can readily insert itself into the M-C bond without forming any meta-stable intermediate. Similar alkyl-olefin complexes such as Cp2NbR( /2-ethylene) have been easily isolated and found not to be the active catalyst precursor of polymerization [31-33, 137]. In support of this, theoretical calculations recently showed the presence of a weakly ethylene-coordinated intermediate (vide infra) [12,13]. The stereochemistry of ethylene insertion was definitely shown to be cis by the evidence that the polymerization of cis- and trans-dideutero-ethylene afforded stereoselectively deuterated polyethylenes [138]. 

Hosokawa, Murahashi, and coworkers demonstrated the ability of Pd" to catalyze the oxidative conjugate addition of amide and carbamate nucleophiles to electron-deficient alkenes (Eq. 42) [177]. Approximately 10 years later, Stahl and coworkers discovered that Pd-catalyzed oxidative amination of styrene proceeds with either Markovnikov or anti-Markovnikov regioselectivity. The preferred isomer is dictated by the presence or absence of a Bronsted base (e.g., triethylamine or acetate), respectively (Scheme 12) [178,179]. Both of these reaction classes employ O2 as the stoichiometric oxidant, but optimal conditions include a copper cocatalyst. More recently, Stahl and coworkers found that the oxidative amination of unactivated alkyl olefins proceeds most effectively in the absence of a copper cocatalyst (Eq. 43) [180]. In the presence of 5mol% CUCI2, significant alkene amination is observed, but the product consists of a complicated isomeric mixture arising from migration of the double bond into thermodynamically more stable internal positions. 

Relative reactivities for the electrophilic carbenes CH3CCI and CCI2 appear in Table 7.3, ° in which they can be seen to react most rapidly with the most highly alkylated olefins, (CH3)2C=C(CH3)2, (CH3)2C=CHCH3, less rapidly with disubstituted frani-butene (designated as the standard alkene, and assigned fcrei = 1.00), and least rapidly with such electron-poor olefins as methyl acrylate or acrylonitrile. 

Yttrium-catalyzed cascade cyclization/hydrosilylation of 3-(3-butynyl)-l,5-hexadienes was stereospecific, and syn-19 (R =Gy, R = OGPh3) underwent cascade cyclization/hydrosilylation to form 80b (R = Gy, R = OGPh3) in 97% yield as a single diastereomer (Scheme 20). The regio- and stereoselective conversion of syn-19 to 80b was proposed to occur through an initial 5- x -intramolecular carbometallation via a chairlike transition state that resembles alkenyl olefin eomplex syn- m. followed by S-exo intramolecular carbometallation via a boatlike transition state that resembles alkyl olefin complex boat-llm. The second intramolecular carbometallation presumably occurs via a boatlike transition state to avoid the unfavorable 1,3-interaction present in the corresponding chairlike transition state (Scheme 20). 

The reaction between isobutane and olefins in the presence of an alkylation catalyst results in a product that is essentially paraffinic, and consists of a mixture of isoparaffins ranging from pentanes to decanes and higher regardless of which alkylating olefin is used. 

Whilst the use of deuterium allows a deeper insight into the mechanism of catalytic reactions than was previously possible, it nevertheless does not allow an absolutely rigorous analysis to be made. One of the major problems in ethylene—deuterium and propene—deuterium studies is that there is no method whereby the true fraction of olefin which has undergone an olefin—alkyl—olefin cycle and reappeared in the gas phase as olefin-d0 can be determined. This is especially true for reactions on metals such as palladium, ruthenium and rhodium where the olefin exchange results sug-... 

Scheme 15 CM of protected amino acids with aryl and alkyl olefins [102]...

Alkylolefins. These cerates convert epoxides into alkylated olefins. DME is... 

The sequence described here illustrates a general procedure for converting ketones into alkylated olefins ... 

To accomplish this either ethylene or propene is combined with isobutane at 50-20°C (125-450°F) and 300-1000 psi (20-68 atmospheres) in the presence of metal halide catalysts such as aluminum chloride. Conditions are less stringent in catal d ic alkylation olefins ( propene, butene, or pentene) are combined with iso-butane in the presence of an acid catalyst (sulfuric acid or hydrofluoric acid) at low temperatures and pressures (1-40°C, 30-105°F, and 14.8-150 psi, 1-10 atmospheres). 

The formation of carboxylic acids from perfluoroalkyl olefins reveals an important influence of the perfluoroalkyl chain on the carbojQ lation process. Thus, no carboxylation occurred in the case of related non-activated alkyl olefins under the same reaction conditions. These results constitute the first example in which an allylic reactivity involving a double bond migration is observed in electrochemical carboxylations. 

Use Catalyst in esterification, alkylation, olefin polymerization, peroxidation reactions. 

In sulfuric acid alkylation, olefins and isobutane react to form a gasoline blending component at around 45 op [6] jjjig reaction only occurs in the acid phase. Olefins are extremely soluble in sulfuric acid isobutane is only slightly soluble. Olefins will polymerize in the absence of isobutane. 

Recently, an organometallic reaction has been elucidated, which clearly confirms that ring closure can occur via alkyl-olefin insertion catalyzed by a Pd(II) complex (97). 

The synthesis of N phthaloyl enamides has been reported by a remarkably general method for aerobic oxidative amination of unactivated alkyl olefins as shown in Scheme 9.6 [12]. From a practical synthesis point of view, the phthalimide can not only serve as a directing group for asymmetric hydrogenation but can also be removed under mild conditions. 

---