O-TMS-diphenylprolinol

The O-TMS-diphenylprolinol 103/BzOH catalytic system is also applicable as an organocatalyst of Michael reactions of nitroalkanes with a, i-enals in aqueous medium [117]. However, functionalized task-specific ionic liquids incorporated in the chiral-pyrrolidine unit, apart from being very efficient and versatile organo-catalysts of Michael and some other asymmetric reactions, show much worse behavior in asymmetric aldol reactions, where their performance is inferior to IL-supported catalysts bearing the a-amino acid fragment [118]. 

General comments about the Michael reaction procedures are analogous to those developed in the aldol and Mannich reactions.For example, the O-TMS-protected diphenylprolinol compound 20 in cooperation with benzoic acid catalyses the asymmetric Michael addition of aldehydes to nitroalkenes, in a simple, practical and efficient procedure. Benzoic acid promotes the rapid formation of the enamine intermediate and the reaction takes place in the highly concentrated organic phase of the aqueous biphasic system. 

In 2009, Chen and coworkers reported a highly enantioselective organocatalytic inverse electron demand HDAR reaction of o-benzoquinone diimides and aliphatic aldehydes catalyzed by a,a-diphenylprolinol (9-TMS ether 269 as a chiral secondary amine (Scheme 2.40) (Li et al. 2009b). 

When the HADR was carried out as in the previously established conditions (Han et al. 2008) o-benzoquinone diimide 268 (1.0 equiv), butanal 253e (2.0 equiv), benzoic acid (10 mol%), and the catalyst a,a-diphenylprolinol 0-TMS ether 269 (10 mol%) in a mixture of MeCN and H2O (10 1) at room temperature, the reaction proceeded smoothly and the desired hemiaminal 270 was isolated as a... 

---