Asymmetric organocatalysts imidazolidinones

The preparation of immobilized catalysts related to the imidazolidinone-type organocatalyst 13 and their application in the asymmetric Diels-Alder reaction was reported by Pihko and co-workers [9]. The reactivity of the immobilized catalysts depended on the type of solid support. The silica-supported imidazolidinone 24, which was prepared starting from N-Fmoc-protected L-phenylalanine, was found to be a highly active organocatalyst. Several dienes and a,/i-un saturated aldehydes have been successfully used in the presence of only 3.3 to 20 mol% 24, usually... 

In addition, immobilized catalysts related to the MacMillan imidazolidinone-type organocatalyst 5 have been used for the asymmetric Diels-Alder reaction (Section... 

The imidazolidinone salt (5.110) has also been used as a catalyst in the asymmetric chlorination of aldehydes. For example, octanal (5.112) is converted into the a-chloroaldehyde with high ee using the antipode of (5.110) and quinone (5.113) as the chlorine source. Jorgensen and coworkers have achieved similar levels of enantioselectivity in this transformation using C2-symmetric diphenylpyrrolidine (5.114) as the organocatalyst in combination with NCS. ... 

The asymmetric a-chlorination of aldehydes has also be achieved using SOMO catalysis (Scheme 13.21) [49]. In these reactions, saturated aldehydes condensed with MacMillan s imidazolidinone organocatalyst to form enamines. The oxidant combination of Cu(TFA)2 and Na2S20g oxidized the enamine to the radical cation (inset in Scheme 13.21), the reactive intermediate in this transformation containing... 

On the other hand, modified-imidazolidinones endowed with imidazole (125) [149] or a fluorous tag in the side chain (126) [150] proved to be active in the Diels-Alder cycloaddition in the presence of 5 vol.% water (Figure 24.40). The highly efficient organocatalyst 127 promoted, in the presence ofp-(trifluoromethyl) benzoic acid, the asymmetric Diels-Alder reaction of cyclohexenones with aromatic nitroolefins in seawater and brine with excellent chemo-, regio-, and stereoselectivities [151]. It has been postulated that the cyclization was involved in a concerted addition process and that seawater and brine significantly promoted the... 

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