Cis/trans product ratios

The hydrogenation of 7 over the catalyst prepared by the reduction of 3 in the absence of any added ligand gave a cis/trans product ratio of 4.0. In addition, a rather large amount of the endo olefin, 10, was also formed. When the catalyst was prepared by the reduction of 3 in the presence of triphenylphosphine (6), a saturated isomer ratio of 2.0 was observed with no double bond isomerization. The same product stereochemistry and lack of double bond isomerization was also found using pre-hydrogenated 1 in the reduction of 7 (3). Thus, one might assume that the catalytic species in these latter two reactions are quite similar, if not identical. 

Hydrogen is not necessary for the reduction of the oxide which can be accomplished merely by stirring 2 in benzene-ethanol for two days under nitrogen. A black solution was thus obtained which was a poor catalyst for the hydrogenation of TBMC (7). A cis/trans product ratio of 3.0 was obtained from this reaction. When 2 was reduced in the presence of 6 the catalyst formed was about 10 times more reactive for the... 

Thioaldehyde S-oxides behave as dienophiles with 1,3-dienes [241]. Cycloaddition involves the carbon-sulfur double bond of the heterocumulene to furnish dihydro-2H-thiapyran S-oxides (Table 6, entry 1). The cis trans product ratio was found to depend upon the initial diene/sulfine ratio. A large excess of diene selectively provided the cis cycloadducts, as a result of a stereospecific reaction of the (Z) sulfine. With a produced proportion of diene, mixtures of cis trans isomers are obtained, with a preference for the cis compound. The Italian authors have demonstrated that the slower reaction allows a (Z) to (E) isomerisation of the sulfines prior to addition. 

The product from Step 4 (0.130 mol), 205 ml of isopropyl alcohol and potassium t-butylate (0.156 mol) were mixed, transferred into a 380 ml stirred stainless steel autoclave, and 4.0 ml of the prepared ruthenium asymmetric catalyst solution added. The mixture was hydrogenated at ambient temperature at 4 x 10 Pa 3 hours. Thereafter, the mixture was filtered, concentrated, and the residue dissolved in a water/ethyl acetate mixture. It was treated with a 5% NH4CI solution and the organic phase dried. HPLC analysis of an aliquot indicated that the cis/trans product ratio was 99 1, respectively, with an enantiomeric excess of (S,S)-cis-l,4-dibenzyl-piperidin-3-ol of 91%. 

At acenaphthylene concentrations as low as 2 10 m, facile photodimerization takes place in benzene in the presence of nonionic or anionic surfactants, whereas in pure benzene at these concentrations no detectable amount of the two dimers is found [720]. Furthermore, the cis/trans product ratio is slightly dependent on the type of surfactant used [720, 721]. The product ratio during the course of photodimerization of 1-substituted acenaphthylenes is influenced by both solvent polarity and the addition of... 

Bond and Wells (4) observed cis/trans ratios < 1 for reactions over metal catalysts. Such results have been interpreted in terms of a radical mechanism in which the stability of the various conformations of the adsorbed butyl radical control the ratio. From energy differences, it can be calculated that the cis/trans ratio should be between 0.5 and 0.8 for the temperature range 0°—150°C. On the other hand, studies over acidic-type catalysts (11, 14) have suggested that if the reaction intermediate is a secondary butyl carbonium ion, then a cis/trans product ratio 1 is to be expected with 1-butene as starting material, and a ron -l-butene... 

The cis and trans diols 55b and 56b are sufficiently reactive in dilute acid solution to undergo equilibration, and the tram diol was determined to be more stable than the cis diol by a factor of 3. In this system, therefore, the major diol from acid-catalyzed hydrolysis is the less stable isomer. This result contrasts with the results from acid-catalyzed hydrolysis of phenyl-substituted cyclohexene oxides, where the major cis diol product is also more stable than the corresponding trans diol. In the hydrolysis of indene oxides 53a, b, therefore, effects that are present in the transition state but absent in the products must play major roles in controlling the cis/trans product ratio. 

An appreciable range of cis-trans product ratios has been found in ring-opening reactions of meta- and pora-substituted 1-phenylcyclohexene oxides. Suspensions of a series of these compounds (276) in 0.02 mol 1 H2SO4 at 25 °C for 24 h gave products (277) and (278) together with 3 % of minor products, which were shown not to be... 

In the different solvents used the cis.trans product ratio varies and, although first-order kinetics operate over more than three half-lives, initial rates only were used. The first-order rate constants are fairly insensitive to the nature of the alcoholic solvent. Unlike the corresponding isomerization of [Pt( -Cl2C— CCl2)(PPhs)2], which apparently occurs by an 5n1 chloride loss and recombination, the chloroalkyne complex isomerizes by an intramolecular pathway more like that found for [Pt( -BrFO= CF2)(AsPh3)2]. These deductions are based on the observed solvent dependence of the rates. 

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