A modularsugar-based phosphoroamidite L1–L5a–g and phosphite L6–L9a–g ligandlibrary was tested in the asymmetric Cu-catalyzed 1,4-conjugate addition reactions of β-substituted (cyclic and linear) and β,β′-disubstituted (cyclic) enones. The selectivity depended strongly on the configuration of carbon atom C-3, the size of the sugar backbone ring, the flexibility of the ligand backbone, the substituents
bidentate P-alkene ligands was observed in the presence of Lewis basic solvents, and model compounds of mono- and bis-solvated species (13, 14) were isolated. Cu formed trigonal-planar neutral (15−17) and cationic complexes (18, 19) of the general formulas [CuI(κ1P-alkene)2] and [Cu(κ1P-alkene)2BF4], respectively (P-alkene = 2, 4, 5). The cationic Rh species 11 catalyzed the 1,4-addition of arylboronic
reaction with various substrates. The most promising results in both reactions were achieved with ligands 11 and 15, which contain a chiral alkene/achiral P-unit or an achiral alkene/chiral P moiety, respectively, and where the metal is complexed on the exo side of the tropene skeleton. In contrast, ligands with an endo coordination mode showed only low (13) or no activity (12) in all of the 1,4-additions
托烷衍生的磷-烯烃杂化配体带有 P-单元(手性 BINOL 衍生单元/非手性 PPh2-单元)与托烯骨架(手性/非手性)的各种组合已被合成并用于 Cu 催化的共轭 1,4-二乙基锌与环烯酮的加成以及在 Rh 催化的苯基硼酸(Hayashi-Miyaura 反应)与环状和非环烯酮的 1,4-加成中。而在 Cu 催化的反应中,只获得了中等的产率和 ee 值(高达 49% ee),而在 Hayashi-Miyaura 反应中观察到高达 97% ee 与各种底物。两个反应中最有希望的结果是用配体 11 和 15 实现的,它们分别包含一个手性烯烃/手性 P 单元或一个非手性烯烃/手性 P 部分,并且金属络合在 tropene 骨架的外侧. 相比之下,具有内配位模式的配体在所有 1,4-添加中仅显示低活性 (13) 或无活性 (12)。NMR 和 ESI-MS 实验表明溶液中存在两种阳离子 [RhI(15)2]+
Catalytic Enantioselective Conjugate Addition of Grignard Reagents to Cyclic Enones Using<i>C</i><sub>1</sub>-1,1′-Bisisoquinoline-Based Chiral Ligands
作者:Gao Qi、Zaher M. A. Judeh
DOI:10.1080/00397911.2010.541969
日期:2012.6
Abstract New highly constrained chiral C 1-1,1′-bisisoquinoline ligands were examined in the enantioselectiveconjugateaddition of Grignard reagents to cyclohexenone and cyclopentenone. The desired 1,4-adducts were obtained in excellent yield and moderate enantiomeric excess (up to 35%). GRAPHICAL ABSTRACT
摘要 在格氏试剂与环己烯酮和环戊烯酮的对映选择性共轭加成中,研究了新的高度受限的手性 C 1-1,1'-双异喹啉配体。以极好的收率和适度的对映体过量(高达 35%)获得了所需的 1,4-加合物。图形概要
Ligand design for dual enantioselective control in Cu-catalyzed asymmetric conjugate addition of R2Zn to cyclic enone
15, which was derived from (S)-tert-leucinol, produced (S)-18 in preference to (R)-18. A series of azolium salts were synthesized from (S)-serine esters, and the reaction conditions for the ECA reaction were optimized to produce (R)-18 with 69% ee. The best results were obtained in the case of the reaction of 4,4-dimethyl-2-cyclohexen-1-one (34) with Et2Zn catalyzed by Cu(OTf)2 in combination with azolium