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J. Am. Chem. Soc. 1997, 119, 10549 10550
Catalytic Pauson Khand Reaction in Super Critical
the homogeneous reaction media after completion of the reaction. The reaction with water soluble ligand bound catalystsin organic/aqueous phase process8 and with perfluorinatedligands bound catalysts in the conventional organic solvent and Nakcheol Jeong,*,† Sung Hee Hwang,† Youn Woo Lee,‡ and perfluorinated solvent system are devised for the operational Meantime, the use of supercritical fluids (Scfs) as reaction Hanhyo Institutes of Technology 461-6 Chonmingdong media is becoming an alternative for the reactions in which the Korea Institute of Science and Technology previously described options are not suitable. The projected P.O. Box 131, Cheongryangri, Seoul, 130-650, Korea advantages of the reactions in supercritical fluids are theincreased reaction rates and selectivities resulting from the high solubility of reactant gases, rapid diffusion of solutes, weakening of the solvation around reacting species, and the local clustering Cocyclization of alkynes with alkenes and carbon monoxide of reactants or solvents.10 It is also interesting to note, in a by cobalt leading to cyclopentenones (known as Pauson Khand practical sense, that those fluids are easily recycled and allow reaction) has been accepted as one of the most powerful tools the separation of dissolved compounds by a gradual release of in the synthesis of cyclopentenones.1 Recent developments in pressure. Sequential and selective precipitations of the catalyst Pauson Khand reaction, especially in the 1990s, have been quite impressive. These include findings of promoters such as Several recent reports have shown that supercritical CO2 (sc silica gel,2 tertiary amine N-oxide,3 and DMSO4 for the CO2) can replace the conventional organic solvents in various stoichiometric reaction, enantioselective reactions,5 and catalytic transformations such as radical reactions,11 Diels Alder reac- versions of the reaction.6 Many variations employing other tion,12 polymerization,13 homogeneous catalytic hydrocarboxy- metals are also reported.7 Despite the successful progress and lation,14 and asymmetric hydrogenations.15 potential implications as an industrial process of this reaction, Herein, we would like to report our preliminary study of the the use of this remarkable reaction has been limited only to the first catalytic Pauson Khand reaction in supercritical fluids.
The catalytic process by dicobalt octacarbonyl had been well This limitation is mainly attributed to the rather low turnover conceived since the discovery of the reaction, but it was in quite number and turnover frequency of the catalytic reaction. More recent years before it was realized.16 To our experiences in severe limitations are associated with the practical operational this field, the control of aggregation status of the catalytic active difficulties such as removal of the catalyst and solvents from species played a critical role. We hoped that the catalytic metals should be well dispersed in Scfs and the chances of the ‡ Korea Institute of Science and Technology.
aggregation of metals would be reduced substantially.
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Synthesis; Trost, B. M., Ed.; Pergamon: Oxford, 1991; Vol. 5, p 1037. (f) Catalytic intramolecular Pauson Khand reactions were per- Schore, N. E. In Comprehesi e Organometallic Chemistry II; Hegedus, L.
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upon warming the mixture to 40 °C, and the reaction mixture Shashkov, A. S.; Mikaelian, G. S.; Tarasov, V. A.; Ibragimov, I. I.; Caple, was further heated up to an appropriate temperature, and the R.; Froen, D. E. Tetrahedron Lett. 1986, 27, 1241.
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minimal amount of the catalyst and various parameters of the (4) Chung, Y. K.; Lee, B. Y.; Jeong, N.; Hudecek, M.; Pauson, P. L.
reaction were roughly defined. Table 1 lists the trials to Organometallics 1993, 12, 220.
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10550 J. Am. Chem. Soc., Vol. 119, No. 43, 1997 Trials To Optimize the PKR Condition in Supercritical CO2 Intramolecular Catalytic PKR in Supercritical CO2 Intermolecular Catalytic PKR in Supercritical CO2 also served as a good substrate albeit an eliminated product wasobtained together with the desired one in the presence of aleaving group (entry 3, Table 2).6 Allyl propargyl ether also produced the corresponding product in excellent yield (entry 4, Table 2), but tosyl and cbz protectedallyl propargyl amine, which were among the best substratesin the conventional catalytic reaction,6b,c remained unreactedunder this condition since they are not reasonably soluble in scCO2 (entry 5, Table 2).
An intermolecular reaction also worked well under this condition. Phenyl acetylene can couple with norbonadiene yield (entries 1, 2, and 4, Table 1). Higher reaction temperature (excess of) to give the bicyclic compound in 87% (entry 1, Table (90 100 °C) beyond critical temperature (31 °C at 72.9 atm) 3). Biscocyclization of diyne proceeded nicely to furnish the is necessary for the completion in a reasonable reaction time bis(bicyclicpentenone) in high yield (entry 2, Table 3).
( 24 h). This reaction mixture requires higher carbon monoxide These preliminary studies demonstrate the feasibility of pressure (15 30 atm) to make the catalytic metal species as conducting transition metal mediated transformations with high intact as possible. Otherwise, the metal catalyst was deactivated by that forming of an unidentified white precipitate.
carbonyl under carbon monoxide pressure will be perfectly fit The scope of the reaction in terms of the substrates was in this special phase due to their favorable solubility profiles.
determined by employing a standard condition as follows: 2.5 We are further optimizing the related reactions in SCFs to define mol % dicobalt octacarbonyl along with 30 atm of CO (at 23 the potential of these novel media and devise environmentally °C) in CO2 (final pressure is 110 120 atm at 36 9 °C) was heated at 90 95 °C for 24 h, and the results are summarized in Supporting Information Available: Representative procedures and
The reaction proceeded pretty well regardless of the substitu- schematic diagram of equipment (3 pages). See any current mastheadpage for ordering and Internet acess instructions.
tion pattern of acetylene. Disubstituted acetylene gave a littlebetter chemical yield (entry 2, Table 2). 1,1′-Disubstituted olefin

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