Pyrrolidines fluorous

Scheme 9.22 Recyclable and reusable pyrrolidine fluorous sulfonamide organocatalysts.

Fluorous aminoesters have also been used in DOS of three unique triaza tricyclic and tetracyclic ring systems (Scheme 22) [44], Bicyclic pyrrolidines 12 generated from one-pot, three-component 1,3-dipolar cycloaddition of azomethine ylides were further converted to hydantoin-, piperazinedione-, and benzodiazepine-fused compounds 31-33, respectively. Each of these three heterocyclic scaffolds has four stereocenters on the central pyrrolidine ring and up to four points of diversity (R1 to R4). The structure of compound... 

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. 

The majority of published work on aza-ylides concerns their applications in synthesis, and here we report a selection of contributions from this area. The Staudinger reaction is a popular route to aza-ylides and has been used to prepare a series of perfluoroalkyl-tagged aza-Wittig reagents, e.g., (68), which were generated in situ (Scheme 22), and utilised in the synthesis of 3//-quinazolidine-4-ones in a fluorous biphasic system. A method for the preparation of aza-polycyclic compounds derived from pyrrolidine, indolizidine and indole has... 

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... 

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]. 

Enantioselective organocatalytic a-chlorination of aldehydes, via enamine catalysis, was independently reported by the groups of MacMillan and Jprgensen in 2004 (Scheme 13.20) [46, 47]. MacMillan utilized his imidazolidinone catalyst and a perchlorinated quinone as the chlorine source, to obtain the S-enantiomer of the a-chloroaldehyde products. Jprgensen employed NCS as the chlorine source, and either a prolinamide catalyst to access the / -enantiomer of the a-chloroaldehyde products, or a Ci-symmetric amine catalyst to access the 5-enantiomer. A recyclable fluorous pyrrolidine-thiourea bifunctional organocatalyst was later employed as an enamine catalyst in this transformation [48]. 

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... 

A fluorous nano-paUadium catalyst based on pyrrolidine imide 22 was developed for the Suzuki coupling reaction (Scheme 7.12) [21]. The catalyst 22 promoted the coupling of aryl boronic acid and aryl halide with high yield, and the catalyst was recovered by fluorous liquid-liquid extraction and reused for three times. This fluorous nano-paUadium catalyst 22 was also employed in the Heck reaction in water [22]. The catalyst was recovered by fluorous liquid-liquid phase separation and reused for four times with Utde loss of catalytic activity. 

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