NHC‐containing chiral bidentate ligands: Synthesis and evaluation in enantioselective copper‐catalyzed conjugate addition

Abstract

New chiral phosphine-, thiolate-, mesylate-, and tosylate-containing N-heterocyclic carbene ligands have been synthesized in fair to excellent yield. These bidentate ligands have been evaluated in enantioselective copper-catalyzed conjugate addition to both cyclic and acyclic enones and displayed good catalytic activities and poor to good enantiomeric excesses (up to 80%).

Tethered NHC Ligands for Stereoselective Alkyne Semihydrogenations

“…To the aqueous phase was then added KPF 6 (1.2 g, 6.6 mmol, 2.0 equiv) and the resulting colorless emulsion was stirred at r.t. for 65 h. The aqueous phase was extracted with CH (8) was prepared according to a literature procedure. 41 To a solution of 5a (1.59 g, 4.20 mmol, 1 equiv) and Et 3 N (0.87 mL, 6.3 mmol, 1.5 equiv) in CH 2 Cl 2 (15 mL) was added a solution of TsCl (1.2 g, 6.3 mmol, 1.5 equiv) in CH 2 Cl 2 (6 mL) dropwise at r.t. The resulting solution was stirred at r.t. for 16 h and diluted with EtOAc (12 mL).…”

Synthesis and Structural Characterization of New Chiral (Biscarbene)platinum(II) Complexes

“…The quest for chiral NHC ligands began in 1996 with the pioneering efforts of Herrmann et al [9] and Enders et al [10] Since then, the impact of these ligands in enantioselective catalysis has been significant. A wide range of stereoselective catalytic transformations catalyzed by chiral di-NHC complexes has been reported, e.g., hydrosilylation, [11][12][13][14] hydrogenation, [15] enantioselective 1,4-conjugate addition [16][17] and transfer hydrogenation. [18] As chirality transfer is a topic of continuously increasing interest, a number of review articles have been published in this field within the past few years, focussing on both successful chirality transfer, and on the limits of strategies designed to extend this very valuable research field into industry.…”

Functionalized N‐Heterocyclic Carbene Ligands for Dual Enantioselective Control in the Cu‐Catalyzed Conjugate Addition of Dialkylzinc Compounds to Acyclic Enones

“…Katsuki and Uchida described the highly enantioselective ACA reactions of alkenyl phenyl ketones with Et 2 Zn catalyzed by Cu(OTf) 2 in combination with the biphenol‐NHC precursor C (Scheme ), which was based on the 1,2‐diphenylethylenediamine skeleton as a source of chirality. Furthermore, Mauduit and co‐workers mentioned that it is impossible to generate a general catalyst for all conjugate addition reactions and extremely difficult to anticipate the reactivity or stereoselectivity of reactions 1d,1h,5e,5g…”