Alkene derivatives interactions

Epoxidation. NaOCl provides the active oxygen for delivery to alkenes through interaction with metal-porphyrin complexes. Typically, 5,10,15,20-tetrakisaryl-porphyrins and their 2,3,7,8,12,13,17,18-octahalo derivatives form active catalysts with metal ions such as Mn. Another heterocyclic ligand (e.g., 4-methylpyridine) and a phase-transfer agent are also added to the reaction medium. 

All of the acylpalladation processes discussed above involve interaction of acylpalladium bonds with C=C bonds. The corresponding acylpalladation of C C bonds proved to be rather elusive. Thus, for example, attempts to observe cyclic acylpalladation of alkyne-containing iodobenzenes totally failed, even though the corresponding alkene derivatives undergo cyclic acylpalladationt (Scheme 23). The contrasting behavior of alkene and alkyne substrates is also schematically summarized in Scheme 23. 

Scheeren et al. reported the first enantioselective metal-catalyzed 1,3-dipolar cycloaddition reaction of nitrones with alkenes in 1994 [26]. Their approach involved C,N-diphenylnitrone la and ketene acetals 2, in the presence of the amino acid-derived oxazaborolidinones 3 as the catalyst (Scheme 6.8). This type of boron catalyst has been used successfully for asymmetric Diels-Alder reactions [27, 28]. In this reaction the nitrone is activated, according to the inverse electron-demand, for a 1,3-dipolar cycloaddition with the electron-rich alkene. The reaction is thus controlled by the LUMO inone-HOMOaikene interaction. They found that coordination of the nitrone to the boron Lewis acid strongly accelerated the 1,3-dipolar cycloaddition reaction with ketene acetals. The reactions of la with 2a,b, catalyzed by 20 mol% of oxazaborolidinones such as 3a,b were carried out at -78 °C. In some reactions fair enantioselectivities were induced by the catalysts, thus, 4a was obtained with an optical purity of 74% ee, however, in a low yield. The reaction involving 2b gave the C-3, C-4-cis isomer 4b as the only diastereomer of the product with 62% ee. 

Dekant W, Vamvakas S, Berthold K, et al. 1986c. Bacterial P-lyase mediated cleavage and mutagenicity of cysteine conjugates derived from the nephrocarcinogenic alkenes trichloroethylene, tetrachloroethylene, and hexachlorobutadiene. Chem Biol Interact 60 31-45. 

Violent explosions which occurred at —100 to —180°C in ammonia synthesis gas units were traced to the formation of explosive addition products of dienes and oxides of nitrogen, produced from interaction of nitrogen oxide and oxygen. Laboratory experiments showed that the addition products from 1,3-butadiene or cyclopentadiene formed rapidly at about — 150°C, and ignited or exploded on warming to —35 to — 15°C. The unconjugated propadiene, and alkenes or acetylene reacted slowly and the products did not ignite until +30 to +50°C [1], This type of derivative ( pseudo-nitrosite ) was formerly used (Wallach) to characterise terpene hydrocarbons. Further comments were made later [2],... 

Numerous reports published in recent years have focused on carbon-centered radicals derived from compounds with selected substitution patterns such as alkanes [40,43,47], halogenated alkanes [43,48,49,51-57], alkenes [19], benzene derivatives [43,47], ethers [51,58], aldehydes [48], amines [10,59], amino acids [23,60-67] etc. Particularly significant advances have been made in the theoretical treatment of radicals occurring in polymer chemistry and biological chemistry. The stabilization of radicals in all of these compounds is due to the interaction of the molecular orbital carrying the unpaired electron with energetically and spatially adjacent molecular orbitals, and four typical scenarios appear to cover all known cases [20]. 

Among oxo-metals, osmium tetroxide is a particularly intriguing oxidant since it is known to oxidize various types of alkenes rapidly, but it nonetheless eschews the electron-rich aromatic hydrocarbons like benzene and naphthalene (Criegee et al., 1942 Schroder, 1980). Such selectivities do not obviously derive from differences in the donor properties of the hydrocarbons since the oxidation (ionization) potentials of arenes are actually less than those of alkenes. The similarity in the electronic interactions of arenes and alkenes towards osmium tetroxide relates to the series of electron donor-acceptor (EDA) complexes formed with both types of hydrocarbons (26). Common to both arenes and alkenes is the immediate appearance of similar colours that are diagnostic of charge-transfer absorp-... 

Yoon and Chae28 have described the DCA-induced photochemical conversion of the cyclopentadiene derivatives 63 into several products. However, only the awri-Bredt adduct 64 is different from those obtained by thermal activation. The experimental data collected have implicated a triplex intermediate 65 in the formation of 64. This triplex is the result of interaction between the diene, the non-conjugated alkene component and the sensitizer. While a mixture of cyclopentadienes was used, it is likely that the products 64 are formed exclusively from the 2-isomer 66. 

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