1.3- Imidazolidin-5-ones Michael reactions

Conjugate addition of nitroalkanes to a,P-unsaturated aldehydes in the presence of imidazolyl-imidazolidin-4-ones was described by Arvidsson and coworkers [92], In addition, silyl enol ethers of substituted acetophenones [93] or thioesters [94] react with a,P-unsaturated aldehydes under iminium-catalysis conditions in the sense of a Mukaiyama-Michael reaction (Scheme 4.24). Applications of this transformation can be found in the total syntheses of compactin [95] and homocitric acid lactone and its homolog [96]. 

Chiral imidazolidin-4-ones-chiral secondary amines-had already been successfully used in asymmetric synthesis before they started their own career as organo-catalysts [1]. They were deployed as chiral auxiliaries for alkylation processes [2], Michael additions [3], and aldol reactions [4], For syntheses of this class of catalyst see Reference [5]. The ability to activate both carbonyl compounds by enamine formation as well a, 3-unsaturated carbonyl compounds by intermediate formation of iminium ions makes imidazolidin-4-ones a valuable class of organocatalysts in both series. Thus, they can roughly be divided by their mode of activation into enamine [6] or iminium [7] catalysis (Scheme 4.1). These catalysts were successfully deployed in a wide range of several important enantioselective C-C bond formation and functionalization processes. Figure 4.1 shows the chiral imidazo-lidinones covered in this chapter. 

Different polymer-supported imidazolidin-4-ones have been deployed in cascade reactions. This strategy was successfully tested in a double Michael addition of methylindole, 2-hexenal, and vinyl methyl ketone [112]. 

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