Bronsted Base-Derived Thiourea Catalysts

The synthetic utility of the bifunctional catalysts in various organic transformations with chiral cyclohexane-diamine derived thioureas was established through the works of Jacobsen, Takemoto, Johnston, Li, Wang, and Tsogoeva. In the last decade, asymmetric conjugate-type reactions have become popular with cinchona alkaloid derived thioureas. The next section presents non-traditional asymmetric reactions of nitroolefins, enones, imines, and cycloadditions to highlight the role of chiral Bronsted base derived thiourea catalysts. 

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Figure 13,6 Basic scaffold of chiral Bronsted base derived thiourea catalysts.

Br0nsted Base-Derived Thiourea Catalysts 353 Chiral Bifunctional Bronsted Base Thiourea Catalyst... 

The roles of the catalytic functions are not necessarily opposite or limited to Lewis acid/base pairs. For example, amine thiourea derivatives like Takemoto s catalyst 4 merge the hydrogen bond donor capability of the thiourea moiety with Bronsted base functionality of the amine function and revealed itself particularly efficient organocatalysts for Michael reactions of various 1,3-dicarbonyl compounds with nitroolefins (Scheme 3) [17-19]. 

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