Diels-Alder reactions in supercritical carbon dioxid

Diels-Alder Reaction in Supercritical Carbon Dioxide (sc-COi)... 

DIELS-ALDER REACTIONS IN SUPERCRITICAL CARBON DIOXIDE... 

The regioselective course of the Diels-Alder reaction in supercritical carbon dioxide was investigated. The analysis failed to confirm the previously reported dramatic effect of reaction conditions on Diels-Alder regiochemistry. The results highlighted the importance of verifying phase behavior when sampling CO2 reaction mixtures and the utility of a view-cell reactor that allows direct monitoring of phase behavior (Ren-slo et al., 1997). 

S. Fukuzawa, K. Metoki, S. Esumi, Asymmetric Diels-Alder reactions in supercritical carbon dioxide catalyzed by rare earth complexes. Tetrahedron 59, 10445-10452(2003). 

Diels-Alder reaction of methyl vinyl ketone (MVK) with iso-prene, the adduct is obtained in 91% yield in the presence of 10 mol % Sc(OTf)3, while 10 mol % Y(OTf)3 or Yb(OTf)3 gives only a trace amount of the adduct.Sc(OXf)3-catalyzed Diels-Alder reactions generally provide high yields with high endo selectivities. The present Diels-Alder reaction even proceeds in aqueous media. Thus, naphthoquinone reacts with cyclopenta-diene in H2O-THF (9 1) at room temperature to give the corresponding adduct in high yield (100% endo) (eq 16). Sc(OTf)3 also serves as an effective catalyst for Diels-Alder reactions in supercritical carbon dioxide (sc C02). ... 

Weinstein, R. D., A. R. Renslo, R. L. Danheiser, J. G. Harris, and J. W. Tester. 1996. Kinetic correlation of Diels-Alder reactions in supercritical carbon dioxide. Journal of Physical Chemistry. 100,12337. 

ME Paulaitis, GC Alexander. Reactions in supercritical fluids. A case study of the thermodynamic solvent effects on a Diels-Alder reaction in supercritical carbon dioxide. Pure Appl Chem 59 61-68, 1987. 

A Renslo, RD Weinstein, JW Tester, RL Danheiser. Concerning the regiochemical course of the Diels-Alder reaction in supercritical carbon dioxide. J Org Chem 62 4530-4533, 1997. 

Y Ikushima, S Ito, T Asano, T Yokoyama, N Saito, K Hatakeda, T Goto. A Diels-Alder reaction in supercritical carbon dioxide medium. J Chem Eng Jap 23 96-98, 1990. 

Y Ikushima, N Saito, O Sato, M Arai. Implications of a transition state in a Diels-Alder reaction in supercritical carbon dioxide. Bull Chem Soc Jpn 67 1734—1736,... 

Dumitrascu and co-workers (52) transformed 4-halosydnones into 5-halopyr-azoles by cycloaddition with DMAD and methyl propiolate followed by retro-Diels-Alder loss of CO2. Turnbull and co-workers (194) reported that the cycloadditions of 3-phenylsydnone with DMAD and diethyl acetylenedicarboxylate to form pyrazoles can be achieved in supercritical carbon dioxide. Nan ya et al. (195) studied this sydnone in its reaction with 2-methylbenzoquinone to afford the expected isomeric indazole-4,7-diones. Interestingly, Sasaki et al. (196) found that 3-phenylsydnone effects the conversion of l,4-dihydronaphthalene-l,4-imines to isoindoles, presumably by consecutive loss of carbon dioxide and A-phenylpyrazole from the primary cycloadduct. Ranganathan et al. (197-199) studied dipolar cycloadditions with the sydnone 298 derived from A-nitrosoproline (Scheme 10.43). Both acetylenic and olefinic dipolarophiles react with 298. In... 

A maximum is found in the ratio of endo- to exo-products versus, density in the Diels-Alder reaction between cyclopentadiene and methyl acrylate in supercritical carbon dioxide (Chfford et al 1997). 

For the Diels-Alder reaction between isoprene and methyl acrylate (see fig. 6.4) in supercritical carbon dioxide at 323 K, the solubility parameter of the activated complex was determined in order to study the nature of the complex and the effect of the solvent on the reaction (Ikushima et al., 1994). 

Table II. Prediction of the Activation volume of the Diels-Alder reaction between isoprene and maleic anhydride in supercritical carbon dioxide at 35 C...

Of the 18 systems, some of which are unstable and must be generated in the reaction has been accomplished for at least 15, but not in all cases with a carbon-carbon double bond (the reaction also can be carried out with other double bonds ). Not all aUcenes undergo 1,3-dipolar addition equally well. The reaction is most successful for those that are good dienophUes in the Diels-Alder reaction (15-60). The addition is stereospecific and syn, and the mechanism is probably a one-step concerted process, as illustrated above, " largely controlled by Frontier Molecular Orbital considerations. " In-plane aromaticity has been invoked for these dipolar cycloadditions. " As expected for this type of mechanism, the rates do not vary much with changes in solvent, " although rate acceleration has been observed in ionic liquids. " Nitrile oxide cycloadditions have also been done in supercritical carbon dioxide. There are no simple rules... 

A variation in this technique has recently been reported, although not necessarily using the high pressures described above. Diels-Alder reactions can be done under pressure in supercritical carbon dioxide., although the synthetic application may be limited by slow reaction rates. Addition of a Lewis acid appears to overcome this problem, as in Kobayashi s use of scandium triflate in the reaction of methyl vinyl ketone with 2-methyl-1,3-butadiene to give a 93 7 mixture of 137/138. " 7a Rayner and co-workers had previously reported the use of scandium triflate in supercritical and observed that the maximum selectivity was obtained... 

Examples of the use of activation volume for the reactions in supercritical fluids is the unimolecular decomposition of a-chlorobenzyl methyl ether in 1,1-difluoroethane Jc = 113.4°C), studied by Johnston and coworkers [54] and the Diels-Alder reaction of isoprene and maleic anhydride in supercritical carbon dioxide [56], described in section 3.1.2.1. In the latter study the large variation in the rate coefficient at 35°C and near-critical pressures was quantified as AV = - 1.39 X lO cm moF in the highly compressible region, as compared with - 38.4 cm mol at 200 bar. Paulaitis and Alexander interpreted their results as a solvent effect stemming from an induced quadrupole moment in the carbon dioxide molecule. 

RD Weinstein, A Renslo, RL Danheiser, JW Tester. Silica-promoted Diels-Alder reactions in carbon dioxide from gaseous to supercritical conditions. J Phys Chem B 103 2878-2887, 1999. 

RS Oakes, TJ HeppenstaU, N Shezad, AA Clifford, CM Rayner. Use of scandium tris(trifluoromethanesulfonate) as a Lewis acid catalyst in supercritical carbon dioxide efficient Diels-Alder reactions and pressure dependent enhancement of endo exo stereoselectivity. Chem Commun 1459-1460, 1999. 

J. Matsuo, T. Tsuchiya, K. Odashima,S. Kobayashi, Lewis add catalysis in supercritical carbon dioxide. Use of scandium tris(heptadecafluo-rooctanesulfonate) as a Lewis add catalyst in Diels-Alder and aza Diels-Alder reactions, Chem. Lett. 29 (2000) 178-179. 

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