Henry Chiral thiourea catalyzed

SCHEME 2.56 Chiral thioureas-catalyzed Michael-Henry reaction for the construction of pyrrolidines. 

SCHEME 2.59 Chiral thioureas-catalyzed Michael-Henry process between cyclohexa-1,4-dione and P-nitrostyrenes. 

Scheme 29.20 Chiral thiourea 37 catalyzed aza-Henry reaction.

In addition to chiral PTCs, cinchona-based thioureas have also been proved to serve as catalysts for nitro-Mannich reactions. In 2006, Ricci and coworkers first reported that the quinine-based thiourea 40 (20mol%) can catalyze the aza-Henry reaction between nitromethane and the N-protected imines 93 derived from aromatic aldehydes [40]. N-Boc-, N-Cbz-, and N-Fmoc protected imines gave the best results in terms of the chemical yields and enantioselectivities (up to 94% ee at —40°C) (Scheme 8.30). 

Mannich Reaction Carbamate-protected alkyl imines are important building blocks in the synthesis of chiral alkyl amines. However, they are usually unstable, and most of them cannot be prepared in pure form. As the optimal substitutes, a-amido sulfones 142 were first used in the PTC-catalyzed enantioselective aza-Henry reaction in 2005 [57]. Subsequently, Song et al. reported a chiral Cinchona alkaloid thiourea (130b)-catalyzed Mannich reaction with in situ generation of... 

---