Bifunctional sulfonamide primary amine

The enantioselective addition of ketones to nitrostyrenes was developed by using the bifunctional sulfonamide primary amine catalyst 93 (Figure 24.32). No reaction took place when water was used as reaction medium. The best solvent was CHCI3. However, addition of water increased the yield and enantioselectivity, probably because it increased catalyst turnover due to facilitating the release of the primary amine catalyst from the imine. Moreover, the authors reported an explanation of the role of water in the enhancement of enantioselectivity [114], Three different primary thiourea-based catalysts (94—96) were also used with very good results (Figure 24.32) [115-117]. 

Asymmetric addition of diorganozincs to aldehydes and ketones has been reviewed, focusing on bifunctional catalysts such as those prepared from salens or BINOLs. Regioisomeric chiral amine-sulfonamide organocatalysts give >99% yield and up to 98% ee in addition of diethylzinc to aldehydes. Switching between regioisomers effectively switches the direction of selectivity. Amino-acid-derived (15,l 5)-4,4 -biquinazoline primary amines catalyse ethylation of aryl aldehydes in up to 95%... 

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