67654-49-3Relevant academic research and scientific papers
SIMPLE CHIRAL CROWN ETHERS COMPLEXED WITH POTASSIUM TERT-BUTOXIDE AS EFFICIENT CATALYSTS FOR ASYMMETRIC MICHAEL ADDITIONS
Aoki, Shin,Sasaki, Shigeki,Koga, Kenji
, p. 7229 - 7230 (2007/10/02)
Simple C2-symmetric chiral crown ether 1 complexed with KOtBu was found to work as an efficient chiral catalyst in Michael additions to cause high asymmetric induction.The results with various chiral crown ethers as catalysts suggest that diaxial-like conformation of the vicinal methyl groups of 1potassium enolate complex is responsible for the chiral induction.
Biomimetic Studies Using Artificial Systems. II. Enantioselective Thiolysis of D- or L-α-Amino Acid Ester Salts by Thiol-Bearing Chiral Crown Ethers as an Enzyme Model
Sasaki, Shigeki,Kawasaki, Motoji,Koga, Kenji
, p. 4247 - 4266 (2007/10/02)
The rates of transacylation were studied between thiol-bearing chiral crown ethers (1-10) and α-amino acid p-nitrophenyl ester salts.Enantioselectivities, kD/kL ratios, of 6.5 for valine ester salt, 8.7 for phenylalanine ester salt, and 7.7 for valine ester salt were achieved by 1, 5, and 8, respectively.Saturation phenomena of rate acceleration depending on crown concentration were observed and analysis of these data revealed that the chiral recognition occurs in the step of liberation of p-nitrophenol by intra-complex thiolysis, not in the complex-forming step.A possible mechanism for the anantioselectivity is proposed on the basis of the kinetic data.Keywords - crown ether; transacylation; pseudo-first-order rate constant; enantioselectivity; thiolysis; intra-complex reaction; enzyme model
Na+ Complexation of New Multidentate Polyether Ligands - Rapid Estimation of Complexation Constants by 23Na NMR Spectroscopy
Offermann, Werner,Weber, Edwin
, p. 234 - 245 (2007/10/02)
A new 23Na NMR method for fast and simple estimation of Na+ complex stabilities is reported and applied to various polyether ligands.Synthesis of the new coronands and podands amongst the employed substrates are given.
