Stereoselective Reactions. 25. Enantioselective Deprotonation of Prochiral 4-Substituted Cyclohexanones by Chiral Chelated Lithium Amides
作者:Ryuichi Shirai、Daisaku Sato、Kazumasa Aoki、Masahide Tanaka、Hisashi Kawasaki、Kenji Koga
DOI:10.1016/s0040-4020(97)00288-3
日期:1997.4
4-substituted cyclohexanones (4a∼d) by chiral chelated lithium amides (8a≈k) in the presence of excess trimethylsilyl chloride was realized to give the corresponding chiral silyl enol ethers (6a∼d) in up to 89% ee. It is shown that enantioselectivity of the reaction is dependent on the solvent used, but becomes almost independent on the solvent in the presence of HMPA. The sense of asymmetric induction
A model has been developed for predicting the diastereoselectivity in the electrophilicamination of chiral1,3,2-oxazaphospholanes derived from ephedrine and pseudoephedrine derivatives. The influence of the five-membered ring conformations and of the bulkiness of the ring substitutents has been deeply analyzed both for reactivity prediction and for 1H-NMR data interpretation. The theoretical and
Vinylborane Formation in Rhodium-Catalyzed Hydroboration of Vinylarenes. Mechanism versus Borane Structure and Relationship to Silation
作者:John M. Brown、Guy C. Lloyd-Jones
DOI:10.1021/ja00082a006
日期:1994.2
Attempted catalytic hydroboration of (4-methoxyphenyl)ethene 1 with R,R-3-isopropyl-4-methyl-5-phenyl-1,3,2-oxazaborolidine 6 proceeded extremely slowly relative to the 3-methyl analog 2 derived from φ-ephedrine when diphosphinerhodium complexes were employed. With phosphine-free rhodium catalysts, especially the 4-methoxyphenylethene complex 7, the reaction proceeded rapidly and quantitatively to
Vinylborane formation in rhodium-catalysed hydroborations; ligand-free homogeneous catalysis
作者:John M. Brown、Guy C. Lloyd-Jones
DOI:10.1039/c39920000710
日期:——
The reaction of vinylarenes with oxazaborolidine 4 catalysed by (bis-alkene) rhodium chloride complexes leads exclusively to coproduction of (E)-vinylborane and ethylarene.