Tranj-Olefin

The relative reactivity of cyclopentadiene and cfxlichloroethylene toward triplet cyclopentadiene was found to be greater than 20 1 while that for cyclopentadiene and /ran dichloroethylene is less than 5 1. Thus the trms isomer is about four times more reactive toward the triplet cyclopentadiene than the cis isomer. An interesting temperature dependence of the product distribution of this reaction has been reported (Table 10.8). The data in Table 10.8 indicate that the relative amount of 1,4 addition [products (39) and (40)] is much more sensitive to temperature than 1,2 addition [products (35)-(38)], especially for the tranj-olefin. The data also indicate that some rotation about the CHCl-CHCl bond occurs in intermediate radicals derived from both cis- and trcnj-dichloroethylene. However, rotational equilibrium is not established at ring closure since the ratios of cij-dichlorocyclobutanes... 

Perfluoro-(l-methylpropenyl)silver undergoes very slow halogen exchange with bromotrichloromethane and 1,2-dibromotetrachloroethane, but gives the tranj-olefins CF3-CF CX CFa (X = Br or H) essentially quantitatively with bromine, water, or hydrogen chloride, and is alkylated with methyl iodide. With cupric bromide it is coupled, presumably via the copper compound CF3 CF CCu-CF3, to give the trfl j,/ra j-isomer of (149). ... 

The utility of tritiozirconations of acetylenes to give tritiated tranj-olefins has been... 

Tranj-dioxoRu(VI) complexes are known to react with olefins according to the classical oxo-transfer mechanism [2] (Fig. 1). The oxoRu(IV) intermediate produced in this process disproportionates readily to give dioxoRu(VI) complex and Ru(II) porphyrin which has strong affinity even towards trace amounts of carbon monoxide. A similar process realized as a side reaction in the rapid oxygenation system would constantly and effectively tie up the catalyst in the catalytically inactive form of Ru (TPFPP)(CO). Indeed, no noticeable changes had been detected in the UV-vis spectrum of the ruthenium porphyrin during the course of Ru (TPFPP)(CO) catalyzed oxidation of cyclohexene. 

There is evidence strongly supporting the two-step mechanism. For example, the zwitterionic intermediate has been trapped, and, furthermore, cis- and tranj -isomeric electrophilic olefins give the same product The reaction has been applied to many different conjugated systems and its regio- and stereoselectivity has been extensively studied . Some examples of this heterocycloaddition include the preparation of 1,4-dihydropyran derivative 331, 332 and 333 by intermolecular reaction. In another example 336 was obtained by intramolecular enamine-enal cycloaddition from... 

The Cr(II) amine complex, formed by rapid addition of an aqueous solution of Cr(Il) perchlorate to a cold solution of ethylenediamine or Et3N in DMF, reduces terminal and alkylphenylacetylene, but not dialkylacetylenes to the corresponding olefin with a high selectivity for the cis-isomer. Propargyl alcohols undergo facile reduction, but with stereoselectivity, the [Cr -ethylenediamine] complex favoring tranj-addition, whereas [Cr -NEt3] favors di-addition °. Tranj-additions is the exclusive pathway in the absence of amine, e.g. ... 

When metathesis is effected with tra i-2-pentene, rather than cis-, and (diphenylcarbene)pentacarbonyltungsten is the initiator, the 2-butene and 2-hexene products are largely trans. The stereospecificity (73-83% trans) is not as great as for cw-olefin metathesis, but it is appreciable (63). The ratios of the stereoisomers in the products are close to the equilibrium ratios, but they probably are not determined by the products equilibrating, for in the short time the metathesis was run to determine the stereochemistry of the initial product, the precursor, tranj-2-pentene, underwent only negligible isomerization. The stereochemistries therefore are determined by the kinetics, which in turn should be affected by conformational factors similar to those in Scheme... 

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