Reactions with ethylene isomer effects

The relative rate constants (fe ) do not account for the fact that approach of the nitrile oxide to the 7i-bond can occur from both olefinic diastereofaces with two regioisomeric modes of reaction (Scheme 6.14). In the case of achiral 1-alkenes, only one regioisomer is formed. With chiral dipolarophiles, preference for one of the two is usually found (diastereodifferentiation). The relative diastereofacial reactivity (fejH) is used to evaluate this effect (121). With ethylene, there are four possibilities of attack (two for each face corresponding to the different regio-isomers), and the of each is set as 0.25. In diastereodifferentiating cycloadditions, such as those with a-chiral alkenes, the major isomer generally results... 

Systematic attempts to improve the yield of y-isomer have been reported.123 Studies were made of the effect of adding compounds such as methyl chloride, chloroform, ethylene, and CS2 that undergo a chain reaction with chlorine, and of adding radical-formers such as... 

The effect of size of the a-substituent was investigated by Tarrant et al. (1964) in the reaction of propynyl-lithium with substituted trifluoro-ethylenes. With X = Cl or Br, the tramjcis ratio of the product was 4 1 and 3 1, while with larger X groups, such as CF3 or CH=CH2, only tram isomers were formed. 

Hexadiene in its E form is manufactured from butadiene and ethylene (Equation 20). The Z isomer must be kept to a minimum owing to its adverse effect on polymerization. The reaction, first reported in 1961, was commercialized by DuPont. The present world production is estimated around 2.5-3 kt/a. Various metal salts (Ni, Co, Fe) were tested, but the best results were obtained with RhCls.hydrate. 

The reaction of HCN with bicyclo[2.2.1]heptene in the presence of Pd[P(OPh)3]4 gave only poor yields of 2-cyanobicyclo[2.2.1]heptane unless P(OPh)3 was also present, in which case a product that was almost exclusively the exo isomer could be obtained (J5). The suggested mechanism is outlined in Fig. 15. The palladium complex will also effectively catalyze the addition of HCN to ethylene. 

A combination of copper bis(dodecylsulfate) and chiral bis(oxazoline) ligands allowed the reaction to occur in neat water in the presence of a catalytic amount of carboxylic acid with ee s up to 69% for the syn isomer.A chiral bis(oxazoline) supported on a modified poly(ethylene glycol) was also shown to be an effective copper(ll) ligand for this aldol reaction in neat water, with 31-63% ee, comparable to those obtained with nonsupported ligands in the same solvent. The solubility of the ligand in water allowed for a highly convenient catalyst recycling procedure. ... 

Cyclometalated catalyst 9 was shown to be effective in the Z-selective ethenolysis of internal olefins (Scheme 8) at relatively low catalyst loadings (0.5 mol%) and ethylene pressures (1-5 atm) [51, 53]. /Z-olefin mixtures were successfully enriched to the pure E-isomer products, with accompanying formation of terminal olefins derived from the Z-isomer. This process was demonstrated to be effective for both linear and cyclic olefins and was found to be tolerant of a number of functional groups including esters, alcohols, amines, and ketones. Reactions were generally conducted at 35°C, which was found to provide an optimal balance with respect to yield and reaction time. Although the reaction is more rapid at... 

Valuable products are produced from the oxidation of both ethylene and propylene (Figs. 1 and 2). Ethylene is epoxidized with oxygen in the vapor phase over a silver catalyst, and propylene is epoxidized with an alkyl hydroperoxide in the liquid phase using a molybdeniim catalyst system. Vinylic oxidation products or their stable isomers, including acetaldehyde, acetone, and vinyl acetate, have been manufactured by a series of related catalytic reactions. These reactions occur either in solutions of palladium complexes or on the surfaces of supported palladium catalysts. Bismuth molybdate is an effective catalyst for allylic oxidations of propylene, which are of paramount importance to the chemical industry. Propylene is oxidized in the vapor phase to give acrolein for acrylic acid manufacture or, in the presence of ammonia, to give acrylonitrile. Second- and third-generation catalysts,... 

Trans effects. In these square-planar olefin complexes, ligands which are trans to the olefin readily undergo displacement reactions [91,92,93]. The trans effect of ethylene is apparent in the greater stability of the white cir-bis-ethylene complex cu-(C2H4)2PtCl2 compared with the very unstable yellow trans isomer [48,14]. The Ironr-isomer readily isomerizes to the cir-isomer in ether solution [94]. 

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