Pyrrolidines fluorous sulfonamide

Scheme 9.22 Recyclable and reusable pyrrolidine fluorous sulfonamide organocatalysts.

Wang and coworkers synthesised recyclable and reusable pyrrolidine-fluorosulfonamide organocatalysts 3b,c. The fluorous sulfonamide organocatalyst 3b was used for the Michael addition of ketones and aldehydes to nitro-olefins in water, and the reaction gave products with high enantio- and diastereomeric purity. Robust organocatalyst 3b was easily separated from... 

Use of fluorous pyrrolidine sulfonamides 5 for enantioselective aldol reactions and Michael additions are shown in Fignre 1.4. The aldol reaction of cyclohexanone and 4-nitrobenzaldehyde under 10 mol% of the catalyst gave product 6 in 90% yield with a 70% ee and a 2 1 syn/anti ratio. The catalyst can be recovered by F-SPE and reused up to 6 times without significant loss of catalytic activity. 

FIGURE 1.4 Fluorous pyrrolidine sulfonamide-catalyzed Michael addition and aldol reaction. 

Diamine catalyst 10, which gives excellent results in the reaction of isobutyr-aldehyde with aromatic aldehydes, affords only moderate diastereoselectivity when used with aliphatic aldehyde donors [119]. Even C2-symmetric catalysts fail to give significant improvements [34c, 139]. Wang reported that the use of fluorous (5)-pyrrolidine sulfonamide 97 in such reactions give better diastereoselectivity and can easily be recovered by simple fluorous solid-phase extraction (Scheme 3.22) [122, 123]. 

In the same context, Wang et al. reported similar highly enantioselective reactions performed in water by using another proline-derived sulfonamide, such as fluorous (5)-pyrrolidine sulfonamide. A notable feature of this simple... 

A slightly different approach is represented by the use of the fluorous (S)-pyrrolidine sulfonamide catalysts 55 (Figure 24.18) [78]. The installation of the... 

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