Asymmetric synthesis with chiral ferrocenylamine ligands: the importance of central chirality

Pastor, Stephen D.; Togni, Antonio

doi:10.1021/ja00188a075

Cited by 130 publications

(32 citation statements)

References 1 publication

(1 reference statement)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Several structural elements are present on the PPF scaffold that could contribute to its successful application in these reactions (51)(52)(53). PPF has elements of central and planar chirality as well as two phosphine atoms that differ both sterically and electronically.…”

Section: Ligand Studies: Variations On the Josiphos Template And Othementioning

confidence: 99%

Rhodium-catalyzed asymmetric ring opening reactions of oxabicyclic alkenes: Catalyst and substrate studies leading to a mechanistic working model

Lautens

Fagnou²

2004

Proc. Natl. Acad. Sci. U.S.A.

101

View full text Add to dashboard Cite

Catalyst and substrate studies have been performed on the rhodium-catalyzed asymmetric ring opening reaction. A working model is advanced that involves oxidative insertion with retention to form an organorhodium intermediate that then undergoes nucleophilic attack with inversion. Kinetic and competition experiments have uncovered evidence for a proton transfer step in the catalytic cycle that may activate both the allylrhodium intermediate and the nucleophile. We have also conducted experiments designed to understand which properties of the PPF-P t Bu2 ligand contribute to the high reactivities and enantioselectivities.W e have previously reported that chiral rhodium(I) catalysts induce ring opening oxa-and azabicyclic alkenes with a variety of soft nucleophiles such as alcohols, phenols, amines, anilines, malonates, and carboxylates in high yield and enantioselectivity (1-8). The products are generated by an S N 2Ј nucleophilic displacement of the bridgehead leaving group with inversion providing the 1,2-trans product as one regio-and diastereomer. The formation of the 1,2-trans products is atypical for ring opening reactions of oxabicyclic alkenes, which usually generate the syn-1,2 diastereomers via exo nucleophilic attack (1, 2). Furthermore, regio-and stereochemical results diverge from previously documented rhodium-catalyzed reactions with allylic carbonates (9-18). The observations obtained with oxabicyclic alkenes find little precedent when compared to other allylic functionalizations including those catalyzed by Pd (refs. 19 In this report we describe catalyst and substrate studies and advance a mechanistic working model that rationalizes the stereochemical outcome and other experimental observations (Scheme 1). We have also conducted experiments designed to understand the properties of the PPF-P t Bu 2 ligand that contribute to high reactivities and enantioselectivities.Experimental procedures and characterization data can be found in Supporting Text, which is published as supporting information on the PNAS web site. Ligand Studies: Variations on the Josiphos Template and Other Ligand MotifsSeveral structural elements are present on the PPF scaffold that could contribute to its successful application in these reactions (51-53). PPF has elements of central and planar chirality as well as two phosphine atoms that differ both sterically and electronically. Two methods were used to determine the influence of the ligand on the rate. In cases where a significant difference in rate was observed, percent conversion vs. time, as determined by crude 1 H NMR, was used to quantify the reactivity of the catalyst. In cases where a more precise measurement of rate was desired, kinetic runs were performed.By comparing the reactivity and enantioselectivity of ligands 3 and 4, two trends emerge (Scheme 2). First, by increasing the steric bulk ( t Bu Ͼ Cy) the enantioselectivity is increased from 88% with 3 to 96% enantiomeric excess (ee) with the bulkier t Bu 2 P ligand 4. This increase in enantioselectivity comes at ...

show abstract

Section: Ligand Studies: Variations On the Josiphos Template And Othementioning

confidence: 99%

Rhodium-catalyzed asymmetric ring opening reactions of oxabicyclic alkenes: Catalyst and substrate studies leading to a mechanistic working model

Lautens

Fagnou²

2004

Proc. Natl. Acad. Sci. U.S.A.

101

View full text Add to dashboard Cite

show abstract

“…Also, the experimental data obtained by Hayashi and Kumada [16 ] for Grignard cross-coupling reactions, when investigating the effect of the central chirality of the stereogenic C-atom of the Josiphos ligand, led them to the conclusion that, in these reactions, planar chirality plays the dominant role in terms of product configuration [16]. Furthermore, Pastor and Togni [17] investigated the effect of ligand chirality on the enantio-and diastereoselectivity of the reaction using (R,S)-, (S,S)-, and (S,R)-configured Josiphos ligands; they concluded that planar and central chirality might act either in a cooperative or in a non-cooperative way, and that, therefore, both stereogenic elements are important [17].…”

mentioning

confidence: 95%

Systematic Study of the Asymmetric Methoxycarbonylation of Styrene Catalyzed by Palladium Systems Containing Chiral Ferrocenyl Diphosphine Ligands

Godard

Ruiz

Claver

2006

Helvetica Chimica Acta

View full text Add to dashboard Cite

Dedicated to Professor Giambattista Consiglio in recognition of his contributions to enantioselective catalysisWe present the first systematic study of the Pd-catalyzed asymmetric methoxycarbonylation of styrene in the presence of chiral ferrocenyl phosphine ligands. The reaction conditions were optimized, and a screening of different catalyst precursors was performed. A number of 1,1'-bis(phosphino)ferrocenes of the Mandyphos, Josiphos, Walphos, and Taniaphos types were tested in combination with [PdCl 2 (NCPh) 2 ], in the presence of TsOH as the acid source. These systems afforded high enantioselectivities, although the regioselectivity of the reaction was found to be in favor of the (undesired) linear ester. The catalytic system made with the Josiphos ligand 1 gave rise to an enantiomeric excess (ee) of 86%.Introduction. -Recently, chiral ferrocenyl phosphine ligands have been successfully used in many catalytic processes [1]. These compounds constitute a family of potentially chelating bi-or tridentate ligands, and their success is largely due to their unique structural features that allow multiple modifications by varying the properties of the substituents on the cyclopentadienyl (Cp) ligands as well as on the P-atoms. The use of ligands bearing analogous metallocenes has also been reported [2].The prototypical ligand 1,1'-bis(diphenylphosphino)ferrocene (dppf) has been extensively used in Pd-catalyzed CÀC and CÀN bond-forming reactions such as cross-coupling [3], Heck reaction [4], carbonylation of chloro arenes [5], aryl halide amination [6], hydroamination of alkynes [7], and methoxycarbonylation of ethene [8]. High enantioselectivities were reported by Xiao and Zhang [9] for the asymmetric hydrogenation of acyclic imines with Ir ferrocene-binaphane complexes [9]. In recent years, 1,2-bis(phosphino)ferrocene has also been used in homogeneous catalysis and given rise to high enantioselectivities in various reactions. For instance, the SolviasJosiphos ligands (Fig. 1), which combine planar chirality with the central chirality of a side group, constitute versatile ligands that can be used in a number of stereoselective processes by simply varying the substituents on the P-atoms [10]. Several related Josiphos ligands are being fruitfully employed in the Rh-catalyzed asymmetric hydrogenation of alkenes on industrial scale. Typically, the enantiomeric excess (ee) obtained in the hydrogenation of dimethyl itaconate (DMI) or methyl 2-acetamidoacrylate (MAA)

show abstract

“…That the absolute configuration of the pseudo benzylic center in ferrocenyl ligands derived from Ugis amine may significantly influence the enantioselectivity of corresponding catalytic reactions is not unprecedented. [15] However, the extent of this effect as observed here is surprisingly high.…”

Section: Resultsmentioning

confidence: 45%

P‐Stereogenic Trifluoromethyl Derivatives of Josiphos: Synthesis, Coordination Properties, and Applications in Asymmetric Catalysis

Buergler

Niedermann

Togni

2011

Chemistry A European J

Self Cite

View full text Add to dashboard Cite

Intermolecular nucleophilic substitution of a CF(3) group of bis(trifluoromethyl)phosphanes by a lithiated Ugi's amine (4) affords both diastereoisomers of the corresponding P-stereogenic trifluoromethylphosphanes 6 and 7. Separation of the isomers by column chromatography on silica gel followed by substitution of the dimethylamino group with phosphanes or pyrazoles yields the bidentate P^P (9 and 10) or P^N ligands (12 and 13) without epimerization at the stereogenic phosphorus center. The coordination properties of these bidentate ligands were investigated on the basis of crystal structures of the corresponding palladium and rhodium complexes. IR spectroscopic measurements of rhodium-carbonyl complexes 16-23 indicated the strongly electronic-withdrawing character of these phosphanes. The catalytic potential of these ligands was demonstrated in the rhodium-catalyzed hydrogenation of olefins as well as in the palladium-catalyzed allylic alkylation reaction, where high activities and enantioselectivities were observed.

show abstract

Asymmetric synthesis with chiral ferrocenylamine ligands: the importance of central chirality

Cited by 130 publications

References 1 publication

Rhodium-catalyzed asymmetric ring opening reactions of oxabicyclic alkenes: Catalyst and substrate studies leading to a mechanistic working model

Rhodium-catalyzed asymmetric ring opening reactions of oxabicyclic alkenes: Catalyst and substrate studies leading to a mechanistic working model

Systematic Study of the Asymmetric Methoxycarbonylation of Styrene Catalyzed by Palladium Systems Containing Chiral Ferrocenyl Diphosphine Ligands

P‐Stereogenic Trifluoromethyl Derivatives of Josiphos: Synthesis, Coordination Properties, and Applications in Asymmetric Catalysis

Contact Info

Product

Resources

About