26164-19-2Relevant academic research and scientific papers
Asymmetric Diels-Alder Reactions of Cyclopentadiene with N-Crotonoyl-1,3-oxazolidin-2-one Derivatives Mediated by Chiral Lewis Acids
Chapuis, C.,Bauer, T.,Jezewski, A.,Jurczak, J.
, p. 2323 - 2332 (2007/10/02)
Diels-Alder reactions of cyclopentadiene with N-crotonoyl-1,3-oxazolidin-2-one derivatives 2b and 2c, mediated by chiral Lewis acids, are described.EtAlCl2, Et2AlCl, AlCl3, TiCl4, modified by D-mannitol, L-tartaric acid, (R)-binaphthol and (R)-camphor lig
Molecular Mechanics Calculations and Comparison of Proton, Fluorine, and Carbon NMR Diastereomer Discrimination via Nonbonding Interactions between Fluorine-Labeled Enantiomeric Amides and Enantiomerically Pure Chiral Solvating Agents
Jursic, Branko S.,Zdravkovski, Zoran
, p. 5245 - 5250 (2007/10/02)
Diastereomer discrimination of fluorine-labeled enantiomers in chloroform solutions was studied with and without two chiral solvating agents (1S and 2S) using 1H, 13C, and 19F NMR spectroscopy.Although by 13C NMR spectroscopy the diastereomer discrimination is not observable, changes of chemical shifts for some carbon atoms unambiguously show formation of nonbonding interactions between the enantiomers and the chiral solvating agents.The position and the ratio of signal sets in both hydrogen and fluorine NMR spectra correspond to the enantiomeric composition in the solution.On the basis of changes in the chemical shifts of enantiomers in chloroform solutions of chiral solvating agent, binding constants and binding energy differences were calculated.Using the MM2 force field, calculations were performed on binding complexes between the chiral solvating agent 2S and enantiomers 6.It was shown that demand for energy differences between diastereomeric nonbonding complexes of racemic amides and the chiral solvating amides necessary to obtain their NMR diastereomer discrimination is low for 1H, intermediary for 19F, and high for 13C NMR.
Conversion of Serine β-Lactones to Chiral α-Amino Acids by Copper-Containing Organolithium and Organomagnesium Reagents
Arnold, Lee D.,Drover, John C. G.,Vederas, John C.
, p. 4649 - 4659 (2007/10/02)
A method for the synthesis of optically pure α-amino acids has been developed.Mono- and di-N-protected α-amino-β-lactones 3a (L, R1=H, R2=COOCH2Ph (Z)), 3b (D, R1=H, R2=Z), 3c (L, R1=CH2Ph, R2=Z), and 3d (D, R1=CH2Ph, R2=Z) are readily produced by cyclization of the corresponding serine derivatives 2 under modified Mitsunobu conditions without loss of optical purity.Stereochemical integrity was demonstrated by conversion of 3 to 2-methoxy-2-(trifluoromethyl)phenylacetate esters 6 and analysis by HPLC, (19)F NMR, and (1)H NMR.Reaction of 3 with organolithium-derived cuprate reagents (R2CuLi or R2Cu(CN)Li2) at low temperature produces N-protected α-amino acids by attack at the β-methylene group.Yields of di-N-protected amino acids are generally higher (ca. 50-75percent), but some decrease in enantiomeric excess (ee) can occur (0-27percent).In contrast, the mono-N-protected β-lactones 3a and 3b give slightly lower yields (ca. 44-62percent) but negligible decrease in ee (0-1.7percent) with the exception of Ph2Cu(CN)Li2 (67percent loss of ee).However, the use of Cu(I)-catalyzed Grignard (RMgCl) additions gives better yields (44-83percent), complete retention of optical purity ( 99.4percent), and fewer side products.Reductive removal of the protecting groups in a single step (H2/Pd-C or Na/NH3) affords the free α-amino acids in 91-99percent yield.Their stereochemical purity was determined by conversion to the corresponding N-(-)-camphanoyl methyl esters and analysis by gas chromatography and (1)H NMR spectroscopy.
