Alkylation, alkenes

Organoboranes undergo transmetallation. 1-Hexenylboronic acid (438) reacts with methyl acrylate via the transmetallation with Pd(OAc)2, giving methyl 2,4-nonadienoate (439)[399], The ( )-alkenylboranes 440, prepared by the hydroboration of terminal alkynes, are converted into the alkylated ( )-alkenes 441 by treatment with an equivalent amount of Pd(OAc)2 and triethylamine[400]. The ( )-octenylborane 442 reacts with CO in MeOH in the... 

Iron porphyrins display pronounced substrate preferences for alkene cyclopro-panation with EDA. In general, electron-rich terminal alkenes in conjunction with aromatic moiety or heteroatoms can efficiently undergo cyclopropanation with high catalyst turnover and selectivity. In contrast, 1,2-disubstituted alkenes cannot undergo cyclopropanation with diazoesters. Alkyl alkenes are poor substrates, giving cyclopropanated products in low yields. In both cases, the dimerization product diethyl maleate was obtained in high yield [53]. 

Using standard references and protocol, we find the three reactions are respectively endothermic by ca 2, 8 and 6 kJmol-1, or ca 2, 4 and 3 kJmol-1 once one remembers to divide by 2 the last two numbers because the allene is dialkylated. So doing, from equations 10 and 11 we find an average ca 3 kJmol-1 (per alkyl group) lessened stability for alkylated allenes than the correspondingly alkylated alkenes. This is a small difference that fits most naturally in the study of substituted cumulenes such as ketenes and ketenimines, i.e. not in this chapter. But it is also a guideline for the understanding of polyenes with more cumulated double bonds. 

A prominent feature of this mechanism is that the growing polymer chain alternately swings between two r/.v-disposed coordination sites during each monomer insertion. General mechanistic outlines of this reaction have been extensively examined by large-scale computations and confirmed by experimental means.59 Our present goal is to clarify the localized donor-acceptor-orbital interactions that underlie (4.106), particularly the nature of the alkyl-alkene complex II. 

Figure 4.77 displays the transition state (II ) between the alkyl-alkene complex II and the final product species III. In this figure one can see that the methide-like... 

On the basis of this simple orbital picture, we can also consider the effect of alternative alkene pendant groups R in the catalytic propagation reaction (4.105). In the case of propylene (R = CH3), for example, one can envision two distinct isomers of the alkyl-alkene complex, with either the primary or the secondary alkene carbon atom as the proximal Cp. This leads to the alternative primary and... 

The second part of the theory, which is a logical consequence of the first, is that monomers that have more than one basic site, e.g., an aromatic ring or an oxygen atom, can form more than one type of complex with the carbenium ion this idea was first proposed by Plesch (1990) in the context of chemically initiated polymerizations. It helps to explain why aryl alkenes and alkyl vinyl ethers polymerize more slowly than isobutene and cyclopentadiene. The reason is that all the complexes formed by the alkyl alkenes are propagators, whereas for the aryl alkenes and vinyl ethers only a fraction of the population of complexes can propagate. 

Ligand 19 was found to be highly selective for the hydrogenation of 1-aryl, I -alkyl alkenes, and ligand 18b was found to be selective for 1-aryl, I -hindered aryl alkenes (Table 7). 

Alkylation [alkenes with alkanes, Eq. (1.7) aromatics, Eq. (1.8)]. —to produce high-octane gasoline and jet-fuel components, detergent alkylates, plastics, intermediates, and other products ... 

Normally, the most practical vinyl substitutions are achieved by use of the oxidative additions of organic bromides, iodides, diazonium salts or triflates to palladium(0)-phosphine complexes in situ. The organic halide, diazonium salt or triflate, an alkene, a base to neutralize the acid formed and a catalytic amount of a palladium(II) salt, usually in conjunction with a triarylphosphine, are the usual reactants at about 25-100 C. This method is useful for reactions of aryl, heterocyclic and vinyl derviatives. Acid chlorides also react, usually yielding decarbonylated products, although there are a few exceptions. Likewise, arylsulfonyl chlorides lose sulfur dioxide and form arylated alkenes. Aryl chlorides have been reacted successfully in a few instances but only with the most reactive alkenes and usually under more vigorous conditions. Benzyl iodide, bromide and chloride will benzylate alkenes but other alkyl halides generally do not alkylate alkenes by this procedure. 

A mixture of 40 and 41 provides the active zinc species 42 in a reaction similar to the Schlenk equilibrium (see Chapter l).22 This presumably alkylates alkene 16 in a bimolecular process via the carbenoid transition structure 44 No free carbenes arise. 

The AcBr-2AlX3 (X = Cl, Br) complexes display high activity in the alkylation of adamantane with alkanes to form poly alkylated adamantanes (Cn < C < C33) and bisadamantylalkanes (C23 < C < C50)119 [Eq. (5.70)]. The suggested pathway includes the 1-adamantyl cation and alkyl cations generated by hydride removal by the superacidic complexes. The 1-adamantyl cation then alkylates alkenes equilibrating with the alkyl cations. Various transformations may follow, resulting in the formation of additional products. 

The bromination depicted in Figure 1.29 proceeds via an unsymmetrical allyl radical. This radical preferentially (80 20) reacts to yield the bromination product with the more highly substituted C=C double bond. As this reaction proceeds under kinetic control, the selectivity is based on product development control the more stable (since higher alkylated) alkene is formed more rapidly than the isomer. 

With allyltrimethylsilane or alkylated alkenes, the leaving group L+ is lost and allylbenzenes are efficiently formed (Scheme 10.14, pathway b). This reaction has been fully explored, and typical examples are illustrated in Scheme 10.16 for allyltrimethylsilane and 2,3-dimethyl-2-butene [12, 13, 26, 27]. This methodology has been effectively applied to the synthesis of naturally occurring phenols with medicinal activity [28]. 

The d group 3 and lanthanide complexes Cp MR are isoelectronic with the [Cp2MR]+ catalysts discussed in the previous section. These nonionic complexes are soluble in most hydrocarbons and as one-component systems make ideal models for many of the fundamental processes in polymerization catalysis. For example, an alkyl-alkene complex can be observed by NMR when Cp 2 YH is allowed to react with an o , )-diene (equation 13). ... 

Many nncleophiles add to one of the double bonds of chelating palladium(diene) complexes to give a chelating Pd alkyl(alkene) derivative, as exemphfied by the reaction of PdCl2(l,5-cod) with methoxide (equation 41). In most cases, the direction of attack is exo. If the nucleophile is in a form that can undergo transmetalation with the Pd l bond, such as Ph2Hg, the nucleophihc group can be delivered endo. In this case, prior formation of a Pd nucleophile bond accounts for the direction of attack (equation 42). 

Apart from the reactions of diazonium salts, a number of other reactions are known in which the C-N bond is broken. The best known of these is the Hofmann elimination of quaternary ammonium hydroxides (Scheme 2.37). An amine is converted by methylation with methyl iodide to the quaternary ammonium salt ( exhaustive methylation ). The iodide, on treatment with moist silver oxide, forms the quaternary ammonium hydroxide which undergoes a bimolecular elimination to form an alkene. The bimolecular elimination of onium salts yields the least alkylated alkene. This substitution pattern is determined by the ease with which a hydrogen atom can be attacked by the base. 

Deoximation. The transformation is carried out in aqueous MeCN at reflux. Friedel-Crafts alkylations. Alkenes and ethers are used as electrophiles in the reaction catalyzed by MofCO). Allyl acetates and alcohols are also suitable substrates. ... 

These relative rates can be explained neither by a simple 1-5 ring closure (Scheme 49), nor by an alkyl-alkene insertion (Scheme 45), which both... 

RM (R = alkyl, alkene, M = metal) were used as nucleophiles, the 1,4-addition became essentially... 

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