Prolinamine and Related Catalysts

Prolinamine catalyst 26 has been introduced for the same purpose [125]. 

With regard to asymmetric aldol reactions, it has been shown that prolinamine catalysts such as 22 can also work well for intramolecular aldol [126-128], Henry (nitroaldol) [129], Mannich [130, 131], and domino-Michael-aldol reactions [132] as valuable asymmetric transformations. 

In this field, prolinamine catalysts 22 and 24 are particularly useful for promoting asymmetric Michael addition reactions between several donor and acceptor molecules [120b, 133-136], On a related topic, catalyst 27 and related diamine or triamine catalysts have been developed [137-139], Interestingly, the Mase/Takabe/ Barbas groups reported that diamine catalyst 25 could again serve as an efficient catalyst for asymmetric Michael addition reactions even in brine solution [140], Similarly, several types of water-active catalysts such as 26 have been developed [141, 142], 

Independently, Alexakis and coworkers reported that 2,2 -bipyrrolidine catalyst 28 showed excellent catalytic activity in several types of asymmetric Michael addition reactions [143]. It has been postulated that the isopropyl group on one of the C2-symmetric pyrrolidine rings should block not only the back face against the approach of Michael acceptors but also shift the equiUbrium towards one of the two rotamers. Since then, closely related catalysts have also been reported [144]. Furthermore, different types of catalysts such as 29 have been shown to be useful in asymmetric Michael addition reactions [145-148]. 

While catalyst 22/23 has been known to be valuable in other C-C bond-forming strategies, for example, 1,3-dipolar cycloaddition [149], hetero-Diels-Alder reaction [150], Friedel-Crafls-type alkylation [151], double-Michael reaction [152], [2,3]-Wittig rearrangement [153], and Claisen-Schmidt condensation [154], only references are given here. 

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