135524-06-0Relevant academic research and scientific papers
General Method for the Synthesis of Enantiomerically Pure β-Hydroxy-α-amino Acids, containing Fluorine Atoms in the Side Chains. Case of Stereochemical Distinction between Methyl and Trifluoromethyl Groups. X-Ray Crystal and Molecular Structure of the Nickel(II) Complex of ...
Soloshonok, Vadim A.,Kukhar, Valeri P.,Galushko, Sergei V.,Svistunova, Nataly Yu.,Avilov, Dimitri V.,et al.
, p. 3143 - 3156 (2007/10/02)
The chiral NiII complex 1 of a Schiff's base derived from (S)-o-benzophenone (BPB) and glycine was treated with fluoro-substituted aldehydes (aliphatic and aromatic) in MeOH or CHCl3.The addition proceeds with high diastereoselectivity to give, if catalysed by MeONa in MeOH, the corresponding complexes of syn-(2R)-3-fluorophenylserines (84-100percent) d.e.) and syn-(2S)-fluoroalkylserines (90percent d.e.), and, if catalysed by NEt3 or DABCO (MeOH or CHCl3), the corresponding complexes of syn-(2S)-, and anti-(2S)-3-fluorophenylserines and fluoroalkylserines.The second-order asymmetric transformation may be successfully employed to obtain diastereoisomerically pure complexes of anti-(2R)-3-fluorophenylserines.Condensation of trifluoroacetone with complex 1, catalysed by MeONa, gave predominantly (at least >95percent d.e.) the diastereoisomeric complex, containing (2S,3S)-β-(trifluoromethyl)threonine, as shown by an X-ray diffraction structural study.Diastereoisomerically and enantiomerically pure fluorine-containing 3-phenyl- and 3-alkyl-serines were obtained from the corresponding diastereomerically pure complexes, separated by chromatography or crystallization.The initial chiral auxiliary BPB was recovered (80-98percent).The influence of the reaction's conditions and the nature of the corresponding fluoro-substituted aldehydes on the diastereoselectivity of the reactions is discussed.
Benzyl (R)- and (S)-tert-Butyl-5-oxo-oxazolidine-3-carboxylate for Convenient Preparation of D- and L-Threonine Analogs from Aldehydes
Blaser, Denis,Seebach, Dieter
, p. 1067 - 1078 (2007/10/02)
Lithium enolates of (R)- or (S)-oxazolidinones 1 (specified in the title) are generated with lithium hexamethyldisilazanide (LHMDS) in THF at -75 deg C and added to aliphatic or aromatic aldehydes (products 2-18 of hydroxyalkylation, yields mostly over 80percent, diastereoselectivities usually over 98percent; Scheme 2).The adducts can be cleaved to give threonine analogs (19-32) under salt-free conditions (H2/Pd-C, then H2O and evaporation of the solvents, Scheme 3).In some cases, the primary adducts may cyclize with elimination of benzyl alcohol to give bicyclic carbamates 33 which, in turn, can be hydrolyzed to 5-substituted trans-2-oxo-1,3-oxazolidine-4-carboxylic acids 34 (Scheme 4). - The essentially complete threo selectivity of the coupling step is proved by NMR spectroscopy and by chemical correlations.The stereochemical course of the reaction is opposite to that observed with carbocyclic enolates; possible reasons for this behavior are discussed (Scheme 5). - The starting material rac-1, prepared from glycine, pivalaldehyde and benzyl chloroformate, is readily resolved by chromatography on preparative scale by using the stationary phase Chiraspher and a Prepbar system (Scheme 1); The undesired enantiomer may be recycled by thermal racemization (heating at reflux in CH3CN for 8 h). Key Words: D- or L-Threonines / Aldol additions / Diastereoselective coupling of trigonal centers / 1,3-Oxazolidin-5-ones / 1,3-Oxazolidin-2-ones, 5-substituted, 4-carboxylic acid
