Directly functionalized olefins

A significant breakthrough in cross metathesis was the discovery of general catalysts for reactions with directly functionalized olefins. The modification of the basic catalyst structure with N-heterocydic carbene ligands opened this area of research. 

Ionic polymers are a special class of polymeric materials having a hydrocarbon backbone containing pendant acid groups. These are then neutralized partially or fully to form salts. lonomeric TPEs are a class of ionic polymers in which properties of vulcanized rubber are combined with the ease of processing of thermoplastics. These polymers contain up to 10 mol% of ionic group. These ionomeric TPEs are typically prepared by copolymerization of a functionalized monomer with an olefinic unsamrated monomer or direct functionalization of a preformed polymer [68-71]. The methods of preparation of various ionomeric TPEs are discussed below. 

Directed rhodium-catalyzed Michael-type additions have recently ketimines with functionalized olefins (Equation (100)).94... 

Very few examples have been reported of the direct carbonation of olefins examples include the direct functionalization of propene [174, 175] and styrene [176, 177]. 

While the selective hydroxylations at C-6 are certainly examples of geometrically directed functionalizations, imitating the enzyme cytochrome P-450, C-6 is not the most attractive target for such selectivity. We wanted to perform a selective multi-turnover hydroxylation of C-9 in the steroid. This would imitate the hydroxylations that take place in fermentations, and would let us convert the product into the 9(11) olefin, as we had done in our directed chlorinations described above. 

Diorganozincs can also be prepared by a nickel-catalyzed hydrozincation. The reaction of Et2Zn with Ni(acac)2 may produce a nickel hydride that adds to an alkene leading after transmetallation with Et2Zn to a diakylzinc (Scheme 9). This reaction proceeds in the absence of solvent and at temperatures of 50-60 °C. A number of functionalized olefins like allylic alcohols or amines can be directly used. This method is especially well suited for the preparation of functionalized diorganozincs for the asymmetric addition to aldehydes (Equation (45)).108,50... 

Oxidation Processes in which the Metal Directly Functionalizes the Olefinic Substrate... 

The use of a formyl group as a directing functionality is challenging because, in the case of the low-valent transition metal-catalyzed reaction of aldehydes with an olefin, aldehydes are prone to undergo decarbonylation or hydroacylation of the olefins. The following protocol to suppress the decarbonylation, one being steric and the other electronic in nature, can be used. In the case of the reaction of 1-methylin-dole-3-carboxaldehyde with ethylene, the ethylation product is also obtained in quantitative yield (Eq. 9.5) [13]. 

Katsuki has studied asymmetric epoxidation of non-functionalized olefins catalyzed by chiral Mn(salen) complex. Recently they proposed that the ligands of Mn(salen) complexes take non-planar stepped conformation and the direction of the folding ligands is strongly related to the sense of chirality in the asymmetric epoxidation (Eq. (7.26)) [71]. On the basis of this proposal, conformational con-... 

Ionomers of practical interest have been prepared by two synthetic routes (a) copolymerization of a low level of functionalized monomer with an olefinically unsaturated monomer or (b) direct functionalization of a preformed polymer. Typically, carboxyl containing ionomers are obtained by direct copolymerization of acrylic or methacrylic acid with ethylene, styrene and similar comonomers by free radical copoly-merization. Rees (22) has described the preparation of a number of such copolymers. The resulting copolymer is generally available as the free acid which can be neutralized to the degree desired with metal hydroxides, acetates and similar salts. Recently, Weiss et al.(23-26) have described the preparation of sulfonated ionomers by copolymerization of sodium styrene sulfonate with butadiene or styrene. 

Functionalized olefins can be classified in two groups the <5-fimctionalized olefins in which the functional group is not directly branched on the double bond but on an alkyl chain of the olefin as in the case of oct-7-en-l-al or linoleic alcohol, and the a-functionalized olefins in which the functional group is directly branched on the double bond as in the case of methyl acrylate or phenyl vinyl ether. The results described for these two groups will be discussed separately. Hydroformylation of water-soluble olefins in two-phase system with water-insoluble catalysts is far beyond the scope of this chapter and will not be discussed here (1, 2]. 

The preparation of ionomers involves either the copolymerization of a functionalized monomer with an olefinic unsaturated monomer or direct functionalization of a preformed polymer. Typically, free-radical copolymerization of ethylene, styrene, or other a-olefins with acrylic acid or methacrylic acid results in carboxyl-containing ionomers. The copolymer, available as a free acid, is then neutralized partially to a desired degree with metal hydroxides, acetates, or similar salts. The second route for the preparation of ionomers involves modification of a preformed polymer. For example, sulfonated polystyrene is obtained by direct sulfonation of polystyrene in a homogeneous solution followed by neutralization of the acid to the desired level. Some commercially available ionomers are listed in Table 15.17. 

Then, the effects of ligands of cobalt(II) complexes in the above reaction was examined and was found that various bis(l,3-diketonato)cobalt(II), especially Co(modp)2, were effectively employed as catalysts. Preparation of a peroxy compound directly from olefin has been considered to be difficult because of its unstability. The present peroxygenation reaction, however, provides a facile and efficient method for the direct introduction of dioxygen function into the carbon-carbon double bond of olefmic compounds under mild conditions (Table 4). In addition, the triethylsilyldioxy derivative here is expected to be a potentially useful synthetic intermediates. 

The discovery, that adhesion to untreated non-polar TPO could be achieved directly through olefinic color coats based on low viscosity functional liquid polymers, might be considered the breakthrough for the TPO industry. Feasibility of the olefmic color coats at bumper plants is also discussed. 

The asymmetric hydrolysis of epoxides, which was impeded by the lack of readily available sources of microbial enzymes, is now possible on a preparative scale. This method offers a valuable alternative to the asymmetric epoxidation of olefins, particularly for those substrates where chemical methods fail due to the absence of directing functional groups. 

In a-functionalized olefins, heteroatoms, such as halogen, oxygen, nitrogen, or sulfur, are connected to the C=C double bond. With unmodified rhodium catalysts, the heteroatom directs the incorporation of the formyl group in a-position. This can be explained by the better stabilization of the branched alkyl-rhodium... 

Only a few examples are reported in the literature of the direct carbonation of olefins, namely the direct functionalization of propene [112, 113] and styrene [108]. Such an approach has a drawback represented by the addition of dioxygen across the C=C double bond with formation of aldehydes or of the relevant acids. Using Rh-complexes the active species in the epoxidation of the olefin has been shown to be the peroxocarbonate moiety [114]. Using differently labeled O2 molecules such as i 08)q 18(16)q possible to build peroxo carbonates... 

In 2011, Sanford et al. developed an elegant Pd(II)-catalyzed, pyridine-directed aerobic olefination of C(sp )-H bonds. The use of air as an external oxidant renders this protocol very promising. It constitutes an extremely rare example of Pd(II)-catalyzed aerobic C(sp )-H bond functionalization in the absence of copper salts additives. The resulting cyclic pyridinium salt can easily afford 6,5-iV-fiised bicyclic framework or alkene product under reductive conditions or organic base. 

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