New Diphosphite Ligands for Catalytic Asymmetric Hydrogenation: The Crucial Role of Conformationally Enantiomeric Diols

Reetz, Manfred T.; Neugebauer, Torsten

doi:10.1002/(sici)1521-3773(19990115)38:1/2<179::aid-anie179>3.3.co;2-q

Cited by 3 publications

(3 citation statements)

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“…Using this principle of induced atropoisomerism, remarkable results were obtained by Mikami and Noyori on Ru-catalyzed hydrogenations, 12 by Bolm on Zr-catalyzed Baeyer-Villiger oxidation, 13 and by Reetz on Rh-catalyzed hydrogenations with biphenol-based phosphites. 14 Some results on the Cu-catalyzed conjugate addition were also reported by Pàmies. 8…”

Section: Methodsmentioning

confidence: 60%

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Novel Biphenol Phosphoramidite Ligands for the Enantioselective Copper-Catalyzed Conjugate Addition of Dialkyl zincs

Alexakis¹,

Rosset²,

Allamand³

et al. 2001

Synlett

174

108

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Phosphoramidite ligands, based on a chiral amine and atropoisomerically flexible biphenols, induce high enantioselectivities (ee's up to 98%) in the copper-catalyzed conjugate addition of dialkyl zinc reagents to a variety of Michael acceptors.There have been many efforts in the field of asymmetric conjugate addition through copper-catalysis. 1 Among the various ways to introduce the chiral information, we demonstrated that trivalent phosphorous ligands were particularly efficient. 2 Later on, we introduced the use of diorganozinc reagents as primary organometallics, 3 and since this first report, in 1993, 3 this combination of a chiral phosphorus ligand and dialkyl zincs has found widespread use, 4-8 although the reaction could be also promoted by non-phosphorus ligands. 9 Typically, cyclohexenone has served as representative Michael acceptor (Scheme 1) with most often Cu(OTf) 2 as copper source (catalyst loading 0.5-2%), in toluene or CH 2 Cl 2 as solvent. Scheme 1Among the many ligands, which have been shown to be efficient, the ones based on a modular concept are of prime importance. Thus, a TADDOL or binaphthol moiety forms a ring with the phosphorus atom, whereas a chiral alcohol or amine is fixed on the exocyclic position ( Figure 1). This combination of two chiral moieties around the phosphorus atom allows for the formation of two diastereomeric ligands. The experimental results show that only one diastereomeric combination affords high enantioselectivities (the matched series) whereas the other one (the mismatched series) does not.For example, ligand L1 affords 96% ee for the conjugate addition of diethylzinc onto cyclohexenone (Scheme 1), whereas the mismatched ligand L1' affords a racemic product. 4d,4e Similarly, ligand L2 affords 98% ee 5 (75% for the mismatched L2') and ligand L3 52% ee 6 (9% for the mismatched L3') for the same reaction. Both mismatched ligands afforded, however, the opposite enantiomer, showing that the binaphthol unit is imposing the absolute stereochemistry of the conjugate adduct. Such behavior of diastereomeric ligands is not unknown and some examples have been reported. 10In the course of our studies to find new ligands, we prepared an equimolecular mixture of ligands L2 and L2', starting from racemic binaphthol. When the reaction was performed using this mixture (Scheme 2), ethyl cyclohexanone was obtained in quantitative yield and with an ee of 66%, corresponding to the enantiomer given by L2! Thus, although each ligand should afford an opposite enantiomer, the matched ligand L2 is largely more efficient and overcomes the mismatched L2'. 11

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Section: Methodsmentioning

confidence: 60%

“…It was known that, in the binaphthol-based ligands (L2 and L3 for example), an ortho subsituent provides improved results. 5b,6b, 13,14 Ligand L5, bearing a methyl group in the ortho position, was designed for that reason. Ligand L6, in contrast, increases the steric bulk at the exocyclic amino moiety.…”

Section: Methodsmentioning

confidence: 99%

Novel Biphenol Phosphoramidite Ligands for the Enantioselective Copper-Catalyzed Conjugate Addition of Dialkyl zincs

Alexakis¹,

Rosset²,

Allamand³

et al. 2001

Synlett

174

108

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“…In addition, the sterically demanding bis(phosphite) ligands have been proved to be able to stabilize the transition metals with low coordination numbers and/or unusual oxidation states, therefore leading to high reactivity which result in good regioselectivity during the catalytic processes. [166][167][168][169] This is still an unexplored field for ligands based on cyclodiphosph(III/III)azane backbones. Herein, we report the first example of an acyclic trimeric cyclodiphosphazane as a potential large bite angle ligand with possible application of stabilizing transition metals with low coordination numbers and/or unusual oxidation states, based on steric bulk.…”

Section: Introductionmentioning

confidence: 99%

Syntheses and characterization of cyclodiphosphazanes and macrocyclodiphosphazanes

Shi¹

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Cofactor-Controlled Chirality of Tropoisomeric Ligand

et al. 2016

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A new tropos ligand with an integrated anion receptor site has been prepared. Chiral carboxylate and phosphate anions that bind in the anion receptor unit proved capable of stabilizing chiral conformations of the achiral flexible bidentate biaryl phosphite ligand, as shown by variable temperature 1 H and 31 P NMR spectroscopical studies of palladium(0) olefin complexes. Palladium allyl complexes of the supramolecular ligand-chiral cofactor assemblies catalyzed asymmetric allylic substitutions of rac-(E)-1,3-diphenyl-2propenyl carbonate and rac-3-cyclohexenyl carbonate with malonate and benzylamine as nucleophiles to provide nonracemic products. Although moderate enantioselectivities were observed, (ee:s up to 66%), the results confirm the ability of the anionic guests to affect the conformation of the ligand.

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New Diphosphite Ligands for Catalytic Asymmetric Hydrogenation: The Crucial Role of Conformationally Enantiomeric Diols

Cited by 3 publications

References 1 publication

Novel Biphenol Phosphoramidite Ligands for the Enantioselective Copper-Catalyzed Conjugate Addition of Dialkyl zincs

Novel Biphenol Phosphoramidite Ligands for the Enantioselective Copper-Catalyzed Conjugate Addition of Dialkyl zincs

Syntheses and characterization of cyclodiphosphazanes and macrocyclodiphosphazanes

Cofactor-Controlled Chirality of Tropoisomeric Ligand

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