866327-29-9Relevant academic research and scientific papers
L-proline-catalyzed asymmetric michael addition of 2-oxindoles to enones: A convenient access to oxindoles with a quaternary stereocenter
Freund, Matthias H.,Tsogoeva, Svetlana B.
, p. 503 - 507 (2011/04/18)
A new organocatalytic approach for 1,4-conjugate addition of 2-oxindoles to α,β-unsaturated ketones using the combination of readily available and nonexpensive l-proline and achiral trans-2,5-dimethylpiperazine as catalytic system is provided. The reaction results in oxindole derivatives with vicinal quaternary and tertiary carbon centers in up to 99% yield and 91% ee. Georg Thieme Verlag Stuttgart.
Highly diastereo- and enantioselective direct aldol reactions of aldehydes and ketones catalyzed by siloxyproline in the presence of water
Aratake, Seiji,Itoh, Takahiko,Okano, Tsubasa,Nagae, Norio,Sumiya, Tatsunobu,Shoji, Mitsuru,Hayashi, Yujiro
, p. 10246 - 10256 (2008/09/18)
Proline-based organocatalysts have been developed for a highly enantioselective, direct aldol reaction of aldehydes and ketones in the presence of water. While several surfactant-proline combined catalysts have proved effective, proline derivatives with a hydrophobic moiety such as rraw-siloxy-L-proline and cis-siloxy-D-proline, both of which are easily prepared from the same commercially available 4-hydroxy-L-proline. have been found to be the most effective organocatalysts examined in this study, affording the aldol product with excellent diastereo- and enantioselectivities, these two catalysts generating opposite enantiomers. Water affects the selectivity, and poor results are obtained under neat reaction conditions or in dry organic solvents. More than three equivalents of water are required for the best diastereo- and enantioselectivities. while three equivalents is the recommended amount from a synthetic point of view. The reaction proceeds in the organic phase, and also proceeds in the presence of a large amount of water. The large-scale preparation of aldols with the minimal use of an organic solvent, including in the purification step. is described.
Organocatalytic entry to chiral bicyclo[3.n.1]alkanones via direct asymmetric intramolecular aldolization
Itagaki, Noriaki,Kimura, Mari,Sugahara, Tsutomu,Iwabuchi, Yoshiharu
, p. 4185 - 4188 (2007/10/03)
(Chemical Equation Presented) The facile stereoselective syntheses of endo-8-hydroxybicyclo[3.3.1]nonan-2-one and encto-7-hydroxybicyclo[3.2.1]octan- 2-one, featuring an α-amino acid catalyzed intramolecular aldolization of σ-symmetric substrates, are des
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).
