Hydrogenation styrene derivatives

Palladation products formed from arylmercurials, carboalkoxymercurials, and alkylmercurials, which have no /3-hydrogen, are used in situ for the reaction of alkenes[367]. Particularly, the arylation of alkenes is synthetically useful. Styrene derivatives 402 and 403 are formed by the reaction of a... 

By using PHIP-NMR studies, various intermediates such as the previously elusive dihydrides of neutral and cationic hydrogenation catalysts, as well as hydrogenation product/catalyst complexes, have already been detected during the hydrogenation of styrene derivatives using cationic Rh catalysts. Information about the substituent effect on chemical shifts and kinetic constants has been obtained via time-resolved PASADENA NMR spectroscopy (DYPAS). 

Styrene derivatives 68-71 (Fig. 30.17 Table 30.13) were hydrogenated with moderate to high selectivity using carbene complexes 13a and 13b [20]. 

Warnmark et al. [12] have reported the formation of a dynamic supramolecular catalytic system involving a hydrogen bonding complex between a Mn(ll I) salen and a Zn(II) porphyrin (Figure 1.4). The salen sub-unit acts as the catalytic center for the catalytic epoxidation of olefins while the Zn-porphyrin component performs as the binding site. The system exhibits low selectivity for pyridine-appended styrene derivatives over phenyl-appended derivatives in a catalytic epoxidation reaction. The... 

Styrene derivatives may be obtained directly from the carbene, by internal hydrogen migration (reaction 3), or from the complex59 (25). 

The Michael addition of doubly deprotonated acetyl acetaldehyde to the nitro-styrene derivative 108 yielded 241, which was converted to 242 by sequential ketalization and catalytic hydrogenation (Scheme 22) (775). Since conventional... 

Heterogeneous systems have also been developed for the cleavage of olefins with hydrogen peroxide.174,175 Titanium-containing zeolites can be used to cleave olefins.176 Adam and co-workers have recently shown that acetophenone, an oxidation product from the Ti-zeolite catalysed oxidation of a-methyl-styrene, derives from 2-hydroxyperoxy-2-phenylpropan-l-ol as an intermediate (which they detected and isolated) (Figure 3.34).177... 

Polymer-supported chiral catalysts have likewise been prepared in order to obtain access to reusable systems (cf. Section 3.1.1, especially Section 3.1.1.3). For example, copolymerized functionalized BINAP [160, 161] could be applied in the enantioselective hydrogenation of olefinic substrates (up to 94 % ee). Similarly, the copolymerization of vinyl-BINAPHOS with styrene derivatives led to a heterogenized auxiliary which made it possible to hydroformylate styrene and vinyl acetate (Rh catalysis) with selectivities and enantioselectivities close to those provided by the parent homogeneous catalytic system [162]. 

Over the years a large variety of monoarylcarbenes have been successfully added to alkenes. Almost all these carbenes belong to the arylmethylene type few examples of cyclopropane formation with alkylarylmethylenes have been reported. This is due to the fact, that the latter type of carbenes are prone to 1,2-hydrogen migration and subsequent formation of styrene derivatives. Thus, when 1-phenyldiazoethane was photolyzed in the presence of ( )-but-2-ene at 5 C, the amount of styrene obtained was the same as the total amount of the three 1,2,3-... 

Aryne interconversion, involving the transfer to benzyne of two hydrogen atoms from adjacent positions of another aromatic compound, is apparently possible at high temperatures (see discussion of thiophen, Section V,B). 1,4-Abstraction of hydrogen atoms by benzyne is the most probable explanation of the aromatization of the Diels-Alder adducts of benzyne and some styrene derivatives under the relatively mild conditions used for benzyne generation from o-bromofluorobenzene or benzenediazonium-2-carboxylate (4) (Scheme 4).24... 

Some papers report on the influence of aromatic compounds on the polymerization of vinyl compounds other than vinyl acetate. Mayo et al.48 found that bromo-benzene acts as a chain transfer agent in the polymerization of styrene, although no fragments of bromobenzene are incorporated into the polymer. They concluded that a complex is formed between the solvent molecule and either the propagating poly-styryl radical or hydrogen atom derived from the latter. 

Fig-4. Models for asymmetric induction in hydrogenation of styrene derivatives... 

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