Cis- s. Isomers, Rearrangement

CIS- s. Isomers, Rearrangement Citric acid esters s. a-Hydroxy-tricarboxylic acid esters Claisen condensation 8, 792 Cleavage (s. a. Lysis)... 

The same reaction occurs, but more slowly, with silver perchlorate. The ci.s-isomers of (1) rearrange more slowly than the /rons-isomers. This rearrangement may be involved in biosynthesis of isoflavones, ... 

Figure 6.21 allows a closer examination of the rearrangement by depicting the absorbance at wavelengths that are characteristic for the aggregated (323 nm) and the nonaggregated frd s-isomers (348 nm), and for the cis-isomer (445 nm). Furthermore, the wavelength of the 7t- t band maximum has been depicted as a function of irradiation time. The irradiation process can be divided in three periods (see the dotted lines in Figure 6.21). The absorbance for both the a egated and nonaggregated chromophores decreases in the first period, but for the aggregated chromophores, it decreases faster. In the second period, the absorbance increases. The uneven decrease of the absorbance at 348 nm and 323 nm results in a shift of the peak maximum for the Ji-Tt band from 323 nm to 340 nm in the decrease period and indicates...

Photochemical Fe(CO)s-induced rearrangement of silylated allyl amine 9 gave N-silylated enamine 10, which on subsequent Cu-catalyzed cyclopropanation by methyl diazoacetate afforded cyclopropane derivative 11. The use of an optically active catalyst gave an asymmetric induction of 56% ee for the cis isomer and 20% ee for the trans isomer. Further acid-induced ring cleavage afforded the j8-formyl ester 12, whereas reduction and desilylation produced aminocyclopropane carboxylic acid 13 (equation 2). 

In these syntheses, Peppard had to rely on the very weak trans effect in the cobalt complex [Co(NH3) i (SO3) 2 ]-. The cis-dichloro-cis-diammineethylenediaminecobalt(III) ion is asymmetric, and Peppard partially resolved it into its enantiomeric forms by adsorption on quartz ground to 100 mesh. This method of resolution is frequently, but not always, effective. Before it can be fully utilized, we will need to learn a great deal more about the principles of adsorption. The preparation of Peppard s isomer s is particularly interesting because cobalt(III) complexes rearrange easily, whereas the platinum compounds do not. 

The situation is more complicated in the case of the pinacolic rearrangement of the isomeric cyclopentane-1,2-diols (Bunton and Carr, 1963b). In aqueous perchloric acid, cis-1, 2-dimethylcyclopentane-l,2-diol (19) is converted into a mixture of the polymeric cyclopentadiene). No O18 is found in the unrearranged cis-diol. The trans-1,2-dimethylcyclopentane-1,2-diol (20), on the other... 

Possible synthetic routes to frinvestigated using the /J-hydroxy-t/3-phosphane oxide alkene inversion procedure. A stepwise approach via the epoxy-trans-cyclononene derivative failed. However, consecutive double elimination involving the bis-/ -hydroxy-) 5-phosphane oxides 11 and 12 gives cis- and trails- 1,2-di-vinylcyclopentanes which are believed to be formed by a rapid Cope rearrangement of parallel and crossed r[Pg.362]

The best studied oxidative addition is that of H2 to the 16e square planar d species, IrCl(CO)(PPh3)2, known as Vaska s complex [97]. This gives anl8e d octahedral Ir(III) dihydride complex (Eq. 2.31). In a concerted addition of this sort, two mutually trans ligands in the starting Ir(I) complex fold back with the result that the cis dihydride isomer is formed, at least initially. Subsequent rearrangement may also occur. 

Cyclopropane derivatives can be prepared by several methods. Michael addition of the enolate of ethyl chloroacetate to ethyl acrylate generated the cyclopropane ring in 7.223 via addition to form a carbanion and internal expulsion of the chlorine moietyl Manipulation of functional groups allowed selective reduction to 7.224 and conversion to 7.225 (as a mixture of cis- and trans-isomers). Rearrangement and hydrolysis led to c/s-2-(2-amino-l-cyclopropyl)ethanoic acid, 7,226. The analogous cyclobutane derivatives were also prepared by a similar route. 

Rose oxide is usually prepared from citronellol which can be converted into a mixture of two allyl hydroperoxides (e.g., by photosensitized oxidation with oxygen). Reduction of the hydroperoxides with sodium sulfite yields the corresponding diols [183]. Treatment with dilute sulfuric acid results in allylic rearrangement and spontaneous cyclization of one of the isomers a mixture of diastereoisomeric rose oxides is thus formed. The unreacted diol isomer is separated by distillation. (—)-Citronellol as the starting material yields approximately a 1 1 mixture of (—)-cis- and (—)-tra s-rose oxide. 

---