1.3- Cyclopentadiene oxidative dimerization

A related rhodium catalyzed enantioselective reductive coupling of acetylene to N arylsulfonyl imines leads to the formation of (Z) dienyl allylic amines (Scheme 1.28) [105]. The scope of the reaction is comparable to that demonstrated for the analogous iridium catalyzed process. The reaction between the acetylene and rhodium leads to the oxidative dimerization of acetylene to form a cationic rhoda cyclopentadiene that then reacts with the imine to generate the product after the protolytic cleavage and reductive elimination. 

Cyclopentadiene (2.5) was prepared from its dimer (Merck-Schuchardt) immediately before use. Dimineralised water was distilled twice in a quartz distillation unit. Ethanol (Merck) was of the highest purity available. Acetonitrile (Janssen) was mn over basic aluminium oxide prior to use. 2,2,2-Trifluoroethanol (Acros) was purified by distillation (bp 79 - C). Co(N03)2 6H20,... 

Sulphines may react as dienophiles with 1,3-dienes with the formation of cyclic sulphoxides. Unstable 2,2-dichloro-5,6-dihydro-2ff-thiin-l-oxide 191 was formed in an exothermic reaction between 173aandcyclopentadieneat — 40 (equation 101). The simplest, parent sulphine, CH2 = S = O, prepared in situ by treatment of a-trimethylsilylmethanesulphinyl chloride with cesium fluoride, reacts with cyclopentadiene to give bicyclic, unsaturated sulphoxide 192 as a mixture of two diastereoisomers in a 9 1 ratio (equation 102). On the other hand, a,j8-unsaturated sulphine 193 (generated by thermolysis of 2-benzylidene-l-thiotetralone dimer S-oxide) in boiling toluene behaves as a 1,3-diene and was trapped by norborene forming sulphoxide 194 in 78% yield ° (equation 103). 

In contrast, exposure of 14-VE (diene)MCp Cl complexes (M = Zr, Hf) to CO (1 atm) results in the formation of cyclopentadienes70. The mechanism proposed for this transformation was elucidated with a carbon labeled CO ( CO) as requiring an initial coordination of CO to generate a (diene)MCp (CO)Cl complex 153 (Scheme 37). For the hafnium complex, the intermediate 153 (M = Hf) was observed by infrared spectroscopy. Insertion of CO into the a2, jt diene generates a metallacyclohexenone, which undergoes reductive elimination to generate the dimeric metallaoxirane species 154. -Hydride elimination from 154 (M = Zr, Hf) followed by 1,2-elimination produces substituted cyclopentadienes and the polymeric metal-oxide 155. Treatment of (diene)TiCp Cl with CO leads to isolation of the metallaoxirane complex 154 (M = Ti). 

Biological. Cyclopentadiene may be oxidized by microbes to cyclopentanone (Dugan, 1972). Chemical/Physical. Dimerizes to dicyclopentadiene on standing (Windholz et al., 1983). 

The sodium salt of cyclopentadiene has been reported to condense readily with ethylene oxide, but the reaction appears to be exceedingly complex, 1,w The initial adduct shown in Eq. (894) can react further with ethylene oxide, undergo DieLa-Alder dimerization, or isomerise to give two more j -hydroxyethy]cyolopeDtadienee. Each of... 

Such higher order prerequisites could be fulfilled by ensemble operation of several sites. For example, a dimeric cluster of cuprous ions on silica gel is very active for the oxidation of CO with NzO at room temperature, but isolated cuprous ions are entirely inactive for this reaction 60). More interesting selectivity may be found in the reaction of olefins with methylene complexes the reaction of olefins with mononuclear methylene undergoes an olefin metathesis reaction, but the reaction of ethylene with bridging methylene in /i-CH2Co2(CO)2(Cp)2 61), /<-CH2Fe2(CO)8 (62), and /<-CH2-/i-ClTi(Cp)2Al(Me)2 (65) (Cp = cyclopentadiene) leads to propene formation (homologation reaction). 

Reports of studies on the reactions of diphosphenes have begun to appear. Like (137), (140) is stable towards methanol but is cleaved by hydrogen chloride. The less hindered (143) dimerizes at room temperature in a few hours, and gives cycloaddition products with Sg and cyclopentadiene (Scheme 11). Oxidation... 

H4Ru4(CO)i2 yields (136) and (137) as two previously uncharacterized organo-metallic products, and both may also be prepared by reaction of Ru3(CO)ia with cot (137) is fluxional, and may be carbonylated to yield an Ru2(CO) -(C sHie) derivative. Reaction of (cot)Fe(CO)3 with cot yields (138). H4RU4-(CO)x2 or Ru3(CO)i2 reacts with a cot-cyclopentadiene mixture to yield the fluxional complex (139), and structurally related derivatives may be obtained using chpt-cyclopentadiene and cot-chpt mixtures. Oxidation of (cot)Fe(CX))8-L [L=CO, PPhg, P(OPh)3] with AgPF yields the dimeric cation (140), characterized crystallographically, where L=P(OPh)3. ... 

Methods of determination of the configuration of bicyclo[2,2,l]-heptanols have been reviewed. The platinum-catalysed oxidation of bicyclo-[2,2,l]heptanediols, whose n.m.r. spectra are discussed, gives ° a number of different diketones and hydroxy-ketones. The n.m.r. spectra of adducts of cyclopentadiene with a-methyl-P-acetylacrylic acid, and of dimers of substituted cyclopentadienes, are noted. 

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