Cobalt catalyzed

A similar synthesis starts from commercially available 1,5-hexadiyne and 2-methyl-cyclopent-2-enone. The benzocyclobutene is obtained from a bis-acetylene in a cobalt-catalyzed reaction. It rearranges regio- and stereoselectively to a 3-deoxy steroid derivative. The overall yield from the cyclopentenone was 40% (R.L. Funk, 1977). 

A key intermediate, 163, which possesses all but one chiral center of (+ )-brefeldin, has been prepared by the enantiocontrolled cycloaddition of the chiral fi,/3-unsaturated ester 162 to 154[107], Synthesis of phyllocladane skeleton 165 has been carried out by the Pd-catalyzed cycloaddition of the unsaturated diester 164 and cobalt-catalyzed cycloaddition of alkynes as key reactions[108]. Intramolecular cycloaddition to the vinylsulfone in 166 proceeds smoothly to give a mixture of the trans and cis isomers in a ratio of 2.4 1[109], Diastereocontrolled cycloaddition of the hindered vinylsulfone 167 affords a single stereoisomeric adduct, 168, which is used for the synthesis of the spirocarbocyclic ring of ginkgolide[l 10],... 

In contrast to triphenylphosphine-modified rhodium catalysis, a high aldehyde product isomer ratio via cobalt-catalyzed hydroformylation requires high CO partial pressures, eg, 9 MPa (1305 psi) and 110°C. Under such conditions alkyl isomerization is almost completely suppressed, and the 4.4 1 isomer ratio reflects the precursor mixture which contains principally the kinetically favored -butyryl to isobutyryl cobalt tetracarbonyl. At lower CO partial pressures, eg, 0.25 MPa (36.25 psi) and 110°C, the rate of isomerization of the -butyryl cobalt intermediate is competitive with butyryl reductive elimination to aldehyde. The product n/iso ratio of 1.6 1 obtained under these conditions reflects the equihbrium isomer ratio of the precursor butyryl cobalt tetracarbonyls (11). 

Cobalt-catalyzed C—C and C-heteroatom bond formation in transformations of heterocycles 97SL876. 

The first example of homogeneous transition metal catalysis in an ionic liquid was the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate (mp. 78 °C), described by Parshall in 1972 (Scheme 5.2-1, a)) [1]. In 1987, Knifton reported the ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [Bu4P]Br, a salt that falls under the now accepted definition for an ionic liquid (see Scheme 5.2-1, b)) [2]. The first applications of room-temperature ionic liquids in homogeneous transition metal catalysis were described in 1990 by Chauvin et al. and by Wilkes et ak. Wilkes et al. used weekly acidic chloroaluminate melts and studied ethylene polymerization in them with Ziegler-Natta catalysts (Scheme 5.2-1, c)) [3]. Chauvin s group dissolved nickel catalysts in weakly acidic chloroaluminate melts and investigated the resulting ionic catalyst solutions for the dimerization of propene (Scheme 5.2-1, d)) [4]. 

Rhodium- and cobalt-catalyzed hydrogenation of butadiene and 1-hexene [47, 48] and the Ru-catalyzed hydrogenation of aromatic compounds [49] and acrylonitrile-butadiene copolymers [50] have also been reported to be successful in ionic liquids. 

Ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [PBuJBr was reported by Knifton as early as in 1987 [2]. The author described a stabilization of the active ruthenium-carbonyl complex by the ionic medium. An increased catalyst lifetime at low synthesis gas pressures and higher temperatures was observed. 

Copper and cobalt catalyze the direct CHZ hydrolysis reaction at temperatures below 275 °F (135 °C), as shown ... 

Consequently, as a result of increasing environmental pressure many chlorine and nitric acid based processes for the manufacture of substituted aromatic acids are currently being replaced by cleaner, catalytic autoxidation processes. Benzoic acid is traditionally manufactured (ref. 14) via cobalt-catalyzed autoxidation of toluene in the absence of solvent (Fig. 2). The selectivity is ca. 90% at 30% toluene conversion. As noted earlier, oxidation of p-xylene under these conditions gives p-toluic acid in high yield. For further oxidation to terephthalic acid the stronger bromide/cobalt/manganese cocktail is needed. 

The Co2(CO)g/pyridine system can catalyze carbomethoxylation of butadiene to methyl 3-pentenoate (Eq. 6.44) [80]. The reaction mechanism of the cobalt-catalyzed carbalkoxylation of olefins was investigated and the formation of a methoxycar-bonylcobalt species, MeOC(0)Co from a cobalt carbonyl complex with methanol as an intermediate is claimed [81, 82]. 

Yong et al. developed a cobalt-catalyzed [2+2+2] cyclotrimerization of terminal alkynes in good yields in aqueous media (80/20 mixture of water and ethanol) at room temperature. A cyclopentadienyl cobalt complex bearing a pendant phosphine ligand was used as a catalyst (Eq. 4.59). The cyclotrimerization of internal alkynes resulted in lower yields and required an elevated temperature, most likely due to steric interactions. For example, cyclotrimerization of 2,5-dimethyl-3-hexyne gave hexaisopropylbenzene in 51% yield and the reaction of diphenylethyne resulted in a 47% yield of hexaphenylbenzene.112... 

The mechanism of [3 + 2] reductive cycloadditions clearly is more complex than other aldehyde/alkyne couplings since additional bonds are formed in the process. The catalytic reductive [3 + 2] cycloaddition process likely proceeds via the intermediacy of metallacycle 29, followed by enolate protonation to afford vinyl nickel species 30, alkenyl addition to the aldehyde to afford nickel alkoxide 31, and reduction of the Ni(II) alkoxide 31 back to the catalytically active Ni(0) species by Et3B (Scheme 23). In an intramolecular case, metallacycle 29 was isolated, fully characterized, and illustrated to undergo [3 + 2] reductive cycloaddition upon exposure to methanol [45]. Related pathways have recently been described involving cobalt-catalyzed reductive cyclo additions of enones and allenes [46], suggesting that this novel mechanism may be general for a variety of metals and substrate combinations. 

The cobalt-catalyzed cooligomerization of diynes with nitriles allows a simple one-step synthesis222 of condensed pyridine derivatives including difficultly accessible 5,6,7,8-tetrahydroisoquinolines223 The synthesis is a versatile one in that pyridines condensed with five- and seven-membered carbocyclic rings can also be achieved in moderate yield in similar fashion. Additional attractive features of this simple synthesis are the formation of condensed isoquinolines by the use of functionalized nitriles and the pronounced regioselectivity observed when dissymmetrical diacetylenes are employed (Scheme 148).222... 

Organometallic reactions leading to condensed pyrans containing three or more rings have been achieved by cyclooligomerization processes and by intramolecular coupling. The former type of reaction is based on intramolecular trapping of o-xylylenes produced in cobalt-catalyzed cyclization... 

An example illustrating the synthesis of condensed oxepins by the cobalt-catalyzed reaction of bistrimethylsilylacetylene with a hexa-l,5-diyne derivative is shown in Scheme 175.234 This type of process has been discussed earlier in the context of pyran synthesis (see Scheme 158 in Section V,B,2). 

A cobalt-catalyzed method for arylation of heteroarenes including thiazole and benzothiazole was reported in 2003 <030L3607>. According to this report, the direct C-5 arylation of thiazole with iodobenzene was carried out in the presence of cobalt catalyst [Co(OAc)2/IMes] and cesium carbonate, and a complete reversal of arylation from C-5 to C-2 was observed with the bimetallic Co/Cu/IMes system. This report has been retracted as the laboratory of the senior author has not been able to reproduce the key results disclosed in the communication <06OL2899>. 

Scheme 9. Cobalt-catalyzed cyclotrimerization of propargylated glycosides.90...

SCHEME 10. Synthesis of glycoasterisk using cobalt-catalyzed benzannulation.90... 

Bethune, D.S., C.-H. Kiang, M.S. de Vries, G. Gorman, R. Savoy, J. Vasquez, R. Beyers, Cobalt-catalyzed growth of carbon nanotubes with single-atomic-layer walls. Nature (London), 363(6430), 605-607,1993. 

Bertole, C.J., Mims, C.A., and Kiss, G. 2002. The effect of water on the cobalt-catalyzed Fischer-Tropsch synthesis. J. Catal. 210 84—96. 

The flow-cell design was introduced by Stieg and Nieman [166] in 1978 for analytical uses of CL. Burguera and Townshend [167] used the CL emission produced by the oxidation of alkylamines by benzoyl peroxide to determine aliphatic secondary and tertiary amines in chloroform or acetone. They tested various coiled flow cells for monitoring the CL emission produced by the cobalt-catalyzed oxidation of luminol by hydrogen peroxide and the fluorescein-sensitized oxidation of sulfide by sodium hypochlorite [168], Rule and Seitz [169] reported one of the first applications of flow injection analysis (FTA) in the CL detection of peroxide with luminol in the presence of a copper ion catalyst. They... 

The principal product of the hydroformylation which is most desired in industrial applications is a linear aldehyde. The unmodified, cobalt-catalyzed processes produce a mixture of linear and branched aldehydes, the latter being mostly an a-methyl isomer. For the largest single application—propylene to butyraldehydes—the product composition has an isomer ratio (ratio of percent linear to percent branched) of (2.5 t.0)/l. The isobutyraldehyde cannot be used to make 2-ethylhexanol, and iso-... 

Interception of the reaction sequence at the alkylcobalt carbonyl stage before carbonyl insertion, and hydrogenation of this intermediate, produces an alkane. This undesired side reaction is only minor (1-3%) in cobalt-catalyzed hydroformylation of a nonfunctional olefin, but may become predominant with phenyl- or acyl-substituted olefins. Ethylbenzene has been obtained in >50% yield from styrene (37), and even more alkane was obtained from a-methylstyrene (35). 

The most influential parameter in cobalt-catalyzed hydroformylation was found to be carbon monoxide partial pressure. Piacenti et al. (30) showed this to be influential for both a- and internal olefins. Results are detailed in Tables V and VI. The percent of n-aldehyde rose rapidly as the carbon monoxide partial pressure was increased up to 30-40 atm CO further increase had little effect. 1-Pentene clearly gave a higher percentage of straight-chain aldehyde than 2-pentene, but the difference was insignificant in the lower Pco experiments. 

Conflicting results have been reported for the effects of catalyst concentration in the cobalt-catalyzed reaction. In early work, Hughes and Kirshenbaum (31) reported that these parameters were very influential in determining product composition high temperatures and high catalyst concentrations resulted in products containing decreased amounts of the... 

In addition to the increased proportion of linear product, other differences from the unmodified cobalt-catalyzed reaction may be noted. The... 

The cobalt-catalyzed reaction was studied by isolation of the lactones formed by hydrogenation and lactonization at higher temperatures (73). The hydroformylation was conducted at 140°C and 300 atm, followed by hydrogenation and cyclization at 200°-240°C, Eq. (33). 

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