Alkene cyclooctene

Normally, a trans alkene is more stable than its cis isomer. tra/75-Cyclooctene, however, is less stable than c/s-cyclooctene by 38.5 kj/mol. Explain. 

A number of complexes AuCIL have been made those with cycloalkenes are most stable decomposing at 50-100°C. At present, few structural data are available, an exception being for AuCl(cyclooctene) (Figure 4.42) which has a structure with r/2 bonding of the alkene (Figure 4.43) [183]. 

Catalytic cyclopropanation of alkenes has been reported by the use of diazoalkanes and electron-rich olefins in the presence of catalytic amounts of pentacarbonyl(rj2-ris-cyclooctene)chromium [23a,b] (Scheme 6) and by treatment of conjugated ene-yne ketone derivatives with different alkyl- and donor-substituted alkenes in the presence of a catalytic amount of pentacarbon-ylchromium tetrahydrofuran complex [23c]. These [2S+1C] cycloaddition reactions catalysed by a Cr(0) complex proceed at room temperature and involve the formation of a non-heteroatom-stabilised carbene complex as intermediate. 

The isomerization takes place because the excited states, both 5i and T, of many alkenes have a perpendicular instead of a planar geometry (p. 311), so cis-trans isomerism disappears upon excitation. When the excited molecule drops back to the So state, either isomer can be formed. A useful example is the photochemical conversion of c/s-cyclooctene to the much less stable trans isomer." Another interesting example of this isomerization involves azo crown ethers. The crown ether (5), in which the N=N bond is anti, preferentially binds NH4, Li, and Na, but the syn isomer preferentially binds and Rb (see p. 105). Thus, ions can be selectively put in or taken out of solution merely by turning a light source on or off." ... 

Isomerization of ( /Z) isomers is another important transformation. Isomerization of ( ) and (Z-) conjugated amides is effected photochemically " (photo-isomerization " ). There is a rather high energy barrier for the excited state required for (E/Z) isomerization. Isomerization of the C=C units in dienes is also induced photochemically. " Isomerization of cyclic alkenes is more difficult but cyclooctene is isomerized photochemically. " Conjugated aldehydes have been isomerized... 

The hydrogenation activity of the isolated hydrides 3 and 6 towards cyclooctene or 1-octene was much lower than the Wilkinson s complex, [RhCKPPhj) ], under the same conditions [2] furthermore, isomerisation of the terminal to internal alkenes competed with the hydrogenation reaction. The reduced activity may be related to the high stability of the Rh(III) hydrides, while displacement of a coordinated NHC by alkene may lead to decomposition and Rh metal formation. 

A NHC-Cu complex 9 has also been used in the cyclopropanation of 5 and cyclooctene 8 using EDA 6 (Scheme 5.3) [5]. Complex 9 was isolated prior to use and, as in the case of NHC-Ru complex, the cyclopropanation reaction did not display high diastereoselectivity. However, products 7 and 10 were obtained in good to excellent yields depending on the ratio between the alkenes and EDA. Improved yields were obtained when alkenes were used in six- or ten-fold excess. 

Epoxidation of cyclooctene and other alkenes with Oxone (KHSO5) was promoted effectively in an aqueous micellar solution of an amphiphilic ketone (3.3).52 The amphiphilic ketone can be easily derived from hepta(ethylene glycol) monodecyl ether. 

AuCl(alkene)] (alkene = m-cyclooctene. norbornene, CHf/o-dicyclopentadiene ) complexes have been obtained by reaction of [AuCl(CO)] with the alkene.2280,2281 The structure of [AuC1(Ci0H12)] shows the ligand //2-bonded to gold via the C=C bond in the norbornene ring and the molecules are associated into dimers through Au Au interactions.2281... 

Photoproducts arising by a [3 + 2] cycloaddition of s-triazolo[4,3-b]-pyridazine (269) to alkenes have been described.222 Addition to cyclohexene, for example, led to the formation of adducts 270 and 271, and the proposed mechanism is outlined in Scheme 8. The reaction has been extended to include addition to cis- and rans-hex-3-ene,223 cyclooctene,224 and furan.225... 

The reactivities of [Ru "(0)(14-TMC)(X)]"+ and its related 15-TMC, 16-TMC, and CRMes coi lexes with organic substrates have also been examined. " " In contrast to polypyridyl Ru =0 species, these macrocyclic Ru =0 complexes are weak oxidants. They oxidize benzyl alcohol to benzaldehyde but do not react with alkenes at room temperature. The lower oxidizing ability of these systems than the polypyridyl systems is due to their lower values. However, [Ru (0)(H20)(N202)](C104)2, which has a higher H value, is able to catalyze the oxidation of norbornylene, styrene, and cyclooctene by PhlO. " ... 

This complex XV was proved to be an active alkene metathesis catalyst even at 0 °C or room temperature. The in situ generated catalyst XV catalyzed the ROMP of cyclooctene at room temperature at high cydooctene/Ru ratio (Table 8.2 entries 4,5) reaching TOF of more than 17000min. ... 

Alkenes strained by twist or r-bond torsion, such as E-cyclooctene, exhibit much lower barriers due to relief of strain in the TS for the oxygen transfer step. While the epoxidation of symmetrically substituted alkenes normally involve a symmetrical approach to the TT-bond, the TSs for epoxidation of E-cyclooctene and E-l-methylcyclooctene exhibit highly asymmetric transition structures. The AAE = 3.3 kcalmol" for E- versus Z-cyclooctene is clearly a reflection of the relative SE of these two medium ring alkenes (16.4 vs 4.2 kcalmol ) ". The classical activation barrier (AE ) for the highly strained bicyclo[3.3.1]non-l-ene is also quite low (Table 10, Figure 26). In these twist-strain alkenes, the approach of the peracid deviates markedly from the idealized spiro approach suggesting fliat this part of the potential energy surface is quite soft. 

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