Rearrangement trans-cis

Some care must be taken in drawing conclusions from the E/Z or syn/anti selectivity of a given catalyst/alkene combination. The intrinsic stereoselectivity may be altered in some cases by subsequent isomerizations initiated by the catalyst. For example, epimerization of disubstituted vinylcyclopropanes is effectively catalyzed by palladium compounds the cis - trans rearrangement of ethyl chrysanthemate or of chrysanthemic acid occurs already at room temperature in the presence of PdCl2 L2 (L = MeCN, EtCN, PhCN)96 Oxycyclopropane carboxylic esters undergo metal-... 

Introduction of an azabenzene unit into the surfactant backbone permitted light-induced cis-trans rearrangements. A change in conductivity accompanied the cis-to-trans transition. Thus, these LB films offer a basis for the construction of molecular switching devices (Fig. 120) [743-745],... 

Many studies of reactions of this sort have been made by Tsuchiya and his coworkers.36 If no volatile ligand is lost, again several different types of reactions have been found to take place Cis—trans rearrangement ... 

Azo compounds undergo a cis-trans isomerization reaction when exposed to UV, visible, or infrared radiation [41],This cis-trans rearrangement is shown in Scheme 15. In more recent literature the trans isomer is called the E form and the cis isomer is called the Z form. The E form absorbs radiation in the UV region and rearranges to the Z form. This transformation is accompanied by a deepening of the original color, which itself is due to the thermal equilibration of the cis and trans isomers. The Z form rearranges to the E form upon the absorption of infrared or visible radiation. 

The cations [cis-HjRh(dppp)2] and [cis-HjRh[(-l-)-diop]2] are similar to the known [cis-H2Rh[P(CHj)3] ] and show a u(Rh-H) stretch in the IR, a pair of multi-plets in the high-field nuclear magnetic resonance (NMR) at 25°C and two resonances in the P NMR. The lower field resonance for each system is attributed to the mutually trans-P atoms, and that at higher field to the P atoms trans to the hydrides. The presence of two P resonances at all temperatures rules out a cis-trans rearrangement. Both [cis-H2Rh(dppp)2] and [cis-HjRh[(-l-)-diop]2] lose on dissolving in solution under Ar. 

If 1,3- dianions of the typ 81 were intermediates in the ET-catalyzed reversible stereoisomerization of the cyclopropanes 78 and 79, the reverse reaction — formation of the cyclopropanes from such dianions — should also take place. Preparation of the dianion 81a from the cyclopropane cis-78a with Na/K or with Li at —78 °C shows clearly that 81 a is stable at this temperature — although cis/trans rearrangement of the cyclopropanes cis-78 and trans-79 takes place ... 

Experimental evidence points to two different modes of oxidative addition. For R -X, when R is sp2 hybridized, a three-centered mechanism seems to apply (see also Section 7-2-2). This leads to an intermediate where R and X are cis. Because of the high trans effect of R a rapid cis-trans rearrangement likely occurs to give the more stable stereoisomer (equation 12.58).121... 

In a long paper which he published in 1912 (8), Werner described many cis-trans rearrangements which cobalt(III) compounds undergo during replacement reactions. He also described some reactions of optically active complexes, which give optically active products, such as the one shown by the equation... 

Olefins can be prepared efficiently in high purity by pyrolysis of readily accessible phosphinates Double bond migration during cis-trans rearrangement can be prevented by irradiation with filtered light in the presence of diphenyl sulfide or disulfide... 

Nitric acid sodium nitrite cis-trans- Rearrangement... 

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