Diels-Alder reaction in supercritical water

Among the reactions studied in supercritical and subcritical water [77f, 78] the first report on a Diels-Alder reaction appeared in 1997 [79]. 

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Diels-Alder reactions in supercritical water have also been investigated.57 Kolis has shown that Diels-Alder reactions of dienes with various electron-poor dienophiles can be performed in supercritical water with high yields of the desired product without the addition of... 

Harano, Y., Sato, H. andHirata, F., Solvent effects on a Diels-Alder reaction in supercritical water RISM-SCF study, /. Am. Chem. Soc., 2000,122,2289-2293. 

Homogeneous reactions carried out at supercritical conditions within water are organo-metallic reactions and Diels-Alder reactions. Reactions in supercritical water are well studied and will be described in the following section. ... 

Among the organic reactions that have been investigated in aqueous medium, the Diels-Alder cycloaddition has been the most studied owing to its great importance from the synthetic and theoretical point of view [7a, bj. In this section Diels-Alder reactions carried out in water under conventional conditions of temperature and pressure will be illustrated. The use of water at supercritical or near-supercritical conditions will be discussed in Section 6.4. 

It is noted that the Diels-Alder reaction has been done with supercritical and with supercritical water as solvents. Diels-Alder reactions on solid supports have also been reported, and zeolites have been used in conjunction with catalytic agents. ° Alumina has been used to promote Diels-Alder reactions. ° Diels-Alder reactions can be done in ionic liquids,including asymmetric Diels-Alder reactions. ... 

The pinacol/pinacolone rearrangement, which is a typical rearrangement catalyzed by acids, occurs in sub- and supercritical water in a certain temperature range without any addition of acids (Scheme 14.4). The reaction was carried out in the temperature range of 20 to 450 °C [49]. Below 300 °C no reaction was observed. Under most reaction conditions investigated, pinacolone was the only reaction product until conversion was complete. Between 375 and 380 °C and 22.5-25 MPa, 1,2,4-trimethyl-4-isopropencydohexene instead of pinacolone is the main product. This product is formed by the elimination of two molecules of water from pinacol and the subsequent reaction of the elimination product via a Diels-Alder reaction. 

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