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Triethylsulfonium bistriflimide, [S 2.2.2 ][NTf 2 ], has been tested and compared with other ionic liquids and molecular solvents as a medium in Diels-Alder reaction between cyclopentadiene and dimethyl maleate. Triflates and chlorides of different metals have been combined with [S 2.2.2 ][NTf 2 ] and the catalytic activity of the systems formed have been determined. The effect of concentration of the catalysts in sulfonium ionic liquid and reactants on the yield and endo:exo ratio has been established. The representative catalyst-Yb(OTf) 3 ÁxH 2 O in [S 2.2.2 ][NTf 2 ]has been examined in the reaction of cyclopentadiene with various dienophiles. The use of sulfonium ionic liquids permitted recycling the catalysts. For the best four catalytic systems, the products have been isolated.

The use of pyridinium ionic liquids as solvent and catalytic systems based on yttrium salts dissolved in pyridinium ionic liquids for the synthetically important Diels-Alder reaction between cyclopentadiene and ethylvinyl ketone was studied. Both chloride and triflate were active catalysts in cycloaddition, strongly improving the reaction rate and stereoselectivity. The catalytic system-1 mol% YCl 3 /[C 4 -3-C 1 py][OTf] (N-butyl-3-methylpyridinium trifluoromethanesulfonate) proved to be stable under recycling conditions.

Abstract:© Versita Sp. z o.o. Keywords: Ionic liquids • Lewis-acids • Diels-Alder reaction • Norbornene derivativesA comparative study of the Diels-Alder reactions between cyclopentadiene (1) and dienophiles (2 a -c) in N-hexylpyridinium bis(trifluoromethylsulfonyl)imide in a temperature range of 20 -45 o C is reported. The reaction rate constants and activation energies were calculated. Moreover, the catalytic systems based on N-hexylpyridinium bis(trifluoromethylsulfonyl)imide and Lewis acids were tested as a reaction media to perform the Diels-Alder reaction. Yb, Y, Mg, Zn triflates and chlorides (0.005 to 0.1 mmol) were used as catalysts. The recycling of catalytic system consisted of YCl3 and ionic liquid was performed.