54665-21-3Relevant academic research and scientific papers
Dual stereocontrol in aldol reactions catalysed by hydroxyproline derivatives in the presence of a large amount of water
Gurka, András A.,Sz?ri, Kornél,Bartók, Mihály,London, Gábor
supporting information, p. 936 - 942 (2016/09/13)
Parameters influencing dual stereocontrol in aldol reactions of water miscible acetone with aromatic aldehydes in the presence of a large amount of water using hydroxyproline based catalysts were studied. Stereocontrol was achieved by changing the acidity and basicity of the reaction media by the addition of achiral salts in the presence of a single chiral catalyst. Under acidic conditions (NH4Cl salt) the (R)-aldol product was formed in excess while basic aqueous media (carboxylate salts) led to the enrichment of the (S)-enantiomer. Reaction conditions under which the reaction is feasible were optimised and the effect of the structure of the hydroxyproline-based catalysts was investigated. The results show that the formation of a biphasic micellar system and the presence of an appropriate catalyst are both crucial for the reaction to occur. Although the catalyst structure influenced the formation and stabilisation of the micellar system to a large extent, its effect on the enantioselectivities were found to be less pronounced.
Tuning the sense of product stereochemistry in aldol reactions of acetone and aromatic aldehydes in the presence of water with a single chiral catalyst
Gurka, András A.,Szori, Kornél,Szollosi, Gy?rgy,Bartók, Mihály,London, Gábor
supporting information, p. 7201 - 7205 (2015/12/12)
We report the aldol addition of acetone to aromatic aldehydes in the presence of a large amount of water where the stereochemical outcome of the reactions can be tuned with achiral salt additives using a single proline-derived catalyst. Depending on the nature of the added salt the (R) and (S) enriched products could be obtained. In the reaction of 2-nitrobenzaldehyde with acetone, NaOAc promoted the formation of the (S)-enantiomer (20% ee) while using NH4Cl the (R)-enantiomer was obtained in excess (58% ee). A similar inversion was observed for several other aromatic aldehydes.
New simple hydrophobic proline derivatives as highly active and stereoselective catalysts for the direct asymmetric Aldol reaction in aqueous medium
Giacalone, Francesco,Gruttadauria, Michelangelo,Lo Meo, Paolo,Riela, Serena,Noto, Renato
experimental part, p. 2747 - 2760 (2009/10/02)
New 4-substituted acyloxyproline derivatives with different hydrophobic properties of the acyl group were easily synthesized and used as catalysts in the direct asymmetric aldol reaction between cyclic ketones (cyclohexanone and cyclopentanone) and severa
Regioselective synthesis of nitrones by decarboxylative oxidation of N- alkyl-α-amino acids and application to the synthesis of 1-azabicyclic alkaloids
Ohtake, Hiroaki,Imada, Yasushi,Murahashi, Shun-Ichi
, p. 2737 - 2754 (2007/10/03)
Tungstate-catalyzed oxidation of N-alkyl-2a-amino acids with 30% H2O2 solution under phase-transfer conditions gives nitrones regioselectively in good yields: Using this method, stereodivergent synthesis of (R)- and (S)-4- (t-butyldimethylsilyloxy)-1-pyrroline N-oxides ((R)-17a and (S)-17a) was achieved. In addition, (R)- and (S)-3-(t-butyldimethylsilyloxy)-1-pyrroline N-oxides ((R)-45 and (S)-45) were prepared by catalytic oxidation of the corresponding chiral pyrrolidines in a regioselective manner. These chiral cyclic nitrones, 17 and 45 are versatile intermediates for the synthesis of optically active nitrogen heterocycles, since stereoselective additions of carbon nucleophiles to these chiral nitrones can be readily performed. Typically, ZnI2-mediated addition of ketene t-butyldimethylsilyi methyl acetal (29a): to (R)-17a gave the' cis-adduct, methyl (2R,4R)-[1,4-bis(t- butyldimethylsilyloxy)pyrrolidin-2-yl]acetate (cis-30). In contrast, the addition of lithium acetylides 34 to the nitrone (R)-17a gave the trans- adducts, (2S,4R)-2-(1-alkynyl)-4-(t-butyldimethylsilyloxy)-1- hydroxypyrrolidines trans-35. These adducts are useful intermediates for syntheses of the nitrogen heterocycles (3R,5R)-1-aza-3- hydroxybicyclo[3.3.0]octane (37) and (6R,8R)-1-aza-8- hydroxybicyclo[4.30]nonane (38), respectively. The ZnI2-mediated addition of ketene silyl acetal 29a to the nitrone (R)-45 gave methyl (2S, 3R)-[1,3- bis(t-butyldimethylsilyloxy)pyrrolidin-2-yl]acetate (trans-50a), which was used for asymmetric synthesis of the Geissman-Waiss lactone ((-)-49).
