Advances in the chemistry of proline and its derivatives: an excellent amino acid with versatile applications in asymmetric synthesis

Conjugating proline derivatives onto multi-walled carbon nanotubes: Preparation, characterization and catalytic activity in water

“…However, mainly due to its poor solubility in organic solvents, dimethylsulfoxide (DMSO) has to be employed and high catalyst loadings are required. In order to tackle this problem, a variety of proline derivatives containing bioisosteric groups like sulfonamides [8][9][10] and tetrazoles [11] as well as prolinamides [12,13] and substituted diaryl prolinols [14] have been synthesized and frequently employed in organocatalytic transformations [15]. On top of the aforementioned points, we recently reported that fullerene C 60 carrying a covalently attached proline unit efficiently catalyzes the typical asymmetric aldol reaction between acetone and 4-nitrobenzaldehyde, both in DMSO and water [16].…”

Chemoenzymatic synthesis of optically active 2-(2′- or 4′-substituted-1H-imidazol-1-yl)cycloalkanols: chiral additives for (l)-proline

“…The asymmetric O-acylation of related six membered ring alcohols has been previously reported using tert-butyl methyl ether (TBME), PSL-C from Amano Pharmaceuticals and at 45 1C yielding the acetate (R,R)-6a and the alcohol (S,S)-4a in enantiopure form and good yields (entries [1][2][3][4]. 12 Accordingly, PSL-C was selected for the biotransformation of the six-membered ring substituted imidazole derivatives (AE)-4b-e. Optimal kinetic resolutions were attained for the 4-substituted derivatives (4b) and (4c) after 13 h at 30 1C ( Table 2, entries 5 and 6).…”

“…From the toolbox of small organocatalysts, proline is by far one of the most popular ones, as it is cheap, readily available in both enantiomeric forms and can be used for a wide range of synthetic transformations. 2 Among them the direct catalytic aldol reaction is a well-studied and broadly applicable C-C bond-forming reaction, which provides enantiomerically enriched b-hydroxy carbonyl compounds. 3 However, (L)-proline itself presents some major drawbacks, presenting a poor solubility and reactivity in non-polar organic solvents, and can lead to parasitic side reactions that significantly reduce the selective conversion of the aldehyde into the corresponding aldol, requiring high catalyst loadings in order to achieve acceptable yields.…”

Synthesis of D-pantolactone via Combined a Novel Organocatalyst Catalyzed Asymmetric Aldol Reaction and Hydrogenation Catalyzed by Cu-/SiO<sub>2</sub>

“…Because of the above-mentioned highly tunable characteristics (broad cation/anion combinations) and the enhancement of reaction efficiency by using ILs as solvents [25][26], ILs have gained wide recognition in specific engineering, especially as catalysts to catalyze aldol reactions [27][28]. So far poline-related-catalyzed asymmetric aldol reactions have been investigated extensively [29][30][31], but there are few reports on grafting L-histidine onto IL. Herein, L-histidine was selected and grafted onto IL to get a novel type of recyclable catalyst which can be recovered quickly and simply between two cycles by solubility difference between substrate, solvent and the product mixture as illustrated in Figure 1.…”