Catalysed asymmetric reaction of aldehydes with dialkylzinc in the presence of chiral pyridyl alcohols as ligands
摘要:
The synthesis of homochiral pyridyl alcohols (1,2,3a-c) and a catalytic asymmetric addition of dialkylzinc to various aldehydes using 1-3 as ligands are described. Although the reaction of benzaldehyde with Et2Zn in the presence of (S)-1 and (R,R)-2 gave (S)- and (R)-1-phenyl-1-propanol, respectively, in moderate enantiomeric excess (e.e.), tridentate ligands (3a-c) accelerated the reaction to produce the corresponding alcohols in high e.e. Particularly, (S)-3b was found to be the most efficient catalyst, for which asymmetric reactions of various aldehydes with dialkylzinc gave the corresponding alcohols in good to high e.es. (up to 95% e.e.).
Catalysed asymmetric reaction of aldehydes with dialkylzinc in the presence of chiral pyridyl alcohols as ligands
摘要:
The synthesis of homochiral pyridyl alcohols (1,2,3a-c) and a catalytic asymmetric addition of dialkylzinc to various aldehydes using 1-3 as ligands are described. Although the reaction of benzaldehyde with Et2Zn in the presence of (S)-1 and (R,R)-2 gave (S)- and (R)-1-phenyl-1-propanol, respectively, in moderate enantiomeric excess (e.e.), tridentate ligands (3a-c) accelerated the reaction to produce the corresponding alcohols in high e.e. Particularly, (S)-3b was found to be the most efficient catalyst, for which asymmetric reactions of various aldehydes with dialkylzinc gave the corresponding alcohols in good to high e.es. (up to 95% e.e.).
A Highly Active Manganese Catalyst for Enantioselective Ketone and Ester Hydrogenation
作者:Magnus B. Widegren、Gavin J. Harkness、Alexandra M. Z. Slawin、David B. Cordes、Matthew L. Clarke
DOI:10.1002/anie.201702406
日期:2017.5.15
A newhydrogenationcatalyst based on a manganese complex of a chiral P,N,N ligand has been found to be especially active for the hydrogenation of esters down to 0.1 mol % catalyst loading, and gives up to 97 % ee in the hydrogenation of pro‐chiral deactivated ketones at 30–50 °C.
Chiral Synthesis via Organoboranes. 46. An Efficient Preparation of Chiral Pyridino- and Thiopheno-18-crown-6 Ligands from Enantiomerically Pure <i>C</i><sub>2</sub>-Symmetric Pyridine- and Thiophenediols<sup>1</sup>
作者:Guang-Ming Chen、Herbert C. Brown、P. Veeraraghavan Ramachandran
DOI:10.1021/jo980899r
日期:1999.2.1
high de and ee. Asymmetric allylboration of 2,6-pyridinedicarboxaldehyde and 2,5-thiophenedicarboxaldehyde provides the corresponding bis-homoallylic alcohols in very high de and ee. These optically pure diols were converted to the disodium or dipotassium salts and treated with tetra(ethylene glycol) ditosylate to obtain the corresponding chiral pyridino and thiopheno-18-crown-6 ligands. However, the
Asymmetric epoxidation models: An alkyl hydroperoxide dependent change in mehanism
作者:Joel M Hawkins、K.Barry Sharpless
DOI:10.1016/s0040-4039(00)96219-1
日期:1987.1
New Pyridino-18-crown-6 Ligands Containing Two Methyl, Two <i>tert</i>-Butyl, or Two Allyl Substituents on Chiral Positions Next to the Pyridine Ring
作者:Yoichi Habata、Jerald S. Bradshaw、J. Jolene Young、Steven L. Castle、Peter Huszthy、Tongjin Pyo、Milton L. Lee、Reed M. Izatt
DOI:10.1021/jo960474+
日期:1996.1.1
Chiral 2,16-diallyl-, 2,16-dimethyl-, and 2,16-di-tert-butylpyridino-18-crown-6 Ligands have been. prepared by treating the appropriate chiral alpha,alpha'-disubstituted pyridinedimethanol with tetraethylene glycol ditosylate in the presence of base. In these reactions, chiral 2:2 dimers (dipyridino-36-crown-12 derivatives) were also obtained. The log K values for the interaction of these chiral ligands with the enantiomers of (alpha-phenylethyl)ammonium perchlorate (PhEt) and (alpha-(1-naphthyl)ethyl)-ammonium perchlorate (NapEt) were measured using an H-1 NMR titration method in a CDCl3/CD3OD (1/1) solvent mixture. The log K values indicate that these chiral pyridino-18-crown-6 ligands have high complexing abilities and some enantiomeric recognition for the chiral organic ammonium perchlorates. The H-1 NMR titration experiments also show that the phenyl ring of the guest PhEt is approximately parallel to the pyridine ring in the chiral diallyl- and dimethyl-substituted Ligand complexes with chiral PhEt and the phenyl ring is perpendicular to the pyridine ring in the chiral di-tert-butyl-substituted ligand complex with PhEt. These results were supported by MM2 calculations.