Thiourea-based organocatalysts Michael addition

On the Bifunctionality of Chiral Thiourea Tertiary-Amine Based Organocatalysts Competing Routes to C-C Bond Formation in a Michael-Addition... 

Another member of the ep -cinchona-based thiourea organocatalyst family, depicted in Scheme 1.19, was applied by Vakulya et al. to the asymmetric Michael addition of nitroalkanes to chalcones, giving excellent yields and enantioselectivities of up to 98% ee. The extension of this methodology was further explored to encompass a,p-unsaturated A-acylpyrroles, as a chalcone mimic. The corresponding Michael products were obtained in high yields and enantioselectivities of up to 94% ee, as shown in Scheme 1.19. This simple novel approach allowed a concise stereoselective synthesis of (i )-rolipram to be accomplished. 

Various thiourea-based bifunctional organocatalysts (e.g. 289a and 372a,b) have been successfully applied for the Michael addition of nitroalkanes RCH2NO2 to 3-ylidene oxindoles (373). The resulting enolate intermediates (374) were then trapped by electrophiles, such as enones, maleimide, and sulfone CH2=C(S02Ph)2. The products were obtained with <99% ee and >95 5... 

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