Chiral <i>C</i><sub>2</sub>-Symmetric Ligands with 1,4-Dioxane Backbone Derived from Tartrates: Syntheses and Applications in Asymmetric Hydrogenation
作者:Wenge Li、Jason P. Waldkirch、Xumu Zhang
DOI:10.1021/jo020250t
日期:2002.11.1
Chiral 1,4-diphenylphosphines 5-7 as well as thioether 8 were synthesized from tartrates employing Ley's "BDA" and "Dispoke" methodologies as the key step. Rhodium(I) complexes with 5-7 are efficient catalysts for the asymmetrichydrogenation of beta-substituted enamides and MOM-protected beta-hydroxyl enamides, which furnished chiral amines or beta-amino alcohols with 94-->99% ee. These results indicated
displayed excellent enantioselectivity and good reactivity in the asymmetric hydrogenation of challenging 1-aryl-substituted dihydroisoquinoline substrates (full conversions, up to >99% ee, 4000 TON). The use of 40% HBr (aqueous solution) as an additive dramatically improved the asymmetric induction of these catalysts. This transformation provided a highly efficient and enantioselective access to chiral
Homochiral NADH models in the pyrrolo[2,3-b]pyridine series bearing one or two chiral auxiliaries. Asymmetric reduction of methyl benzoylformate and N-acetyl-enamines. Influence of the magnesium salt concentration on the asymmetric induction of reductions
models in the pyrrolo[2,3-b]pyridine series bearing one or two chiral auxiliaries either at the pyridine or at the pyrrole ring is described. These models were involved in the reduction of methylbenzoylformate. The reactivity of these reagents and the stereochemical outcome of reductions are discussed in relation to the nature of the chiral auxiliary at the pyrrole ring and the magnesium ions concentration
描述了在吡啶或吡咯环上带有一个或两个手性助剂的吡咯并[2,3- b ]吡啶系列中NADH模型的合成。这些模型参与了甲基苯甲酰甲酸酯的还原。讨论了这些试剂的反应性和还原的立体化学结果,并与吡咯环上手性助剂的性质和镁离子浓度进行了讨论。试剂3在苯甲酰基甲酸酯的还原反应中显示出优异的反应活性,在几分钟内得到对映体过量(ee = 84%)的扁桃酸甲酯。最后,模型1参与了N-乙酰基-烯胺15和16的不对称还原分别是Salsolidine和Carnegine的前体。在这项研究过程中,N-乙酰基-烯胺15的还原度可降低至87%ee
Synthesis of a new chiral bisphosphine ligand, MOCBP, and its use in rhodium(I)-catalyzed asymmetric hydrogenation of a cyclic enamide
作者:Toshiaki Morimoto、Noriya Nakajima、Kazuo Achiwa
DOI:10.1016/0957-4166(94)00355-f
日期:1995.1
A new chiral bisphosphine ligand (6) bearing a cyclobutane framework was readily prepared by using diastereoselective [2+2] cycloaddition. Its rhodium(I) complex was found to be an efficient catalyst for the asymmetrichydrogenation of a cyclic enamide, N-acetyl-1-methylene-1,2,3,4-tetrahydroisoquinoline (9), affording (R)-(−)-N-acetylsalsodine (10) in up to 80.6% ee.
Non chiral and chiral NADH models in the pyrrolo [2,3-b] pyridine series have been synthesized. These reagents 1) allow reductions of substrates previously found to be non reducible with similar reagents, 2) can give either one enantiomer or the other during the reduction of a prochiral ketone depending on the experimental conditions, 3) can be used in the synthesis of chiral precursors of target molecules obtained with good enantiomeric excesses.