Bis-thiourea based ionic organocatalysts

Abstract

Ionic liquids and organocatalysts serve as greener alternatives to conventional reaction solvents and catalysts. Recent research has found that pyrrolidinium tagged ionic organocatalysts enhance the rate of DABCO co-catalyzed Morita-Baylis-Hillman reactions and remain entrained in ionic liquid media. Three bis-thiourea based ionic organocatalysts have been synthesized. 1,1-bis(4-(3-(3,5-bis(trifluoromethyl)phenyl)thioureido)benzyl)pyrrolidinium hexafluorophosphate(V) was successfully employed in the DABCO co-catalyzed rate enhancement of the reaction between benzaldehyde and cyclohex-2-en-1-one. 95 % conversion to product was attained at 5 mol% catalyst loading. This room-temperature reaction used the ionic liquid N-butyl-N-methylpyrrolidiniumbis(trifluoromethane)sulfonamide, [BMPyr][N(Tf)[subscript 2]], as the reaction solvent. Attempts at recycling the catalyst resulted in low conversion with no evidence of catalyst leaching. Microwave irradiation of the MBH reactions was attempted, with low conversion to product attributed to thermal degradation of the catalyst.