Nonlinear stereochemical effects in asymmetric reactions

Авалос, M.; Babiano, Reyes; Cintas, Pedro; Jimenez, J. L.; Palacios, Juan C.

doi:10.1016/s0957-4166(97)00375-3

Cited by 164 publications

(44 citation statements)

References 79 publications

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“…Such aggregations of intermediates Scheme 3 have already been suggested as an explanation of nonlinear stereochemical effects in asymmetric catalysis. [31,32] Moreover, for 2-hydroxy-3-pinanone itself, the value of optical rotation does not correlate linearly with the optical purity. This effect was explained by solute/solute interactions.…”

Section: Resultsmentioning

confidence: 97%

Stereoselective Synthesis of γ-Fluorinated α-Amino Acids Using 2-Hydroxy-3-pinanone as an Auxiliary

et al. 2000

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Keywords: Amino acids / Fluorine / Chiral auxiliaries / 2-Hydroxy-3-pinanone / 1-Bromo-2-fluoroethane / 3-Bromo-2-fluoropropene (+)-(S)-2-Amino-4-fluorobutanoic acid (5a) (Ͼ 96% ee), its α-methylated derivative (+)-(S)-5b (85% ee), and (−)-(S)-2-amino-4-fluoro-4-pentenoic acid (10) (81% ee) were synthesized by diastereoselective alkylation in the presence of LDA at low temperatures. Alkylation of (+)-(R,R,R)-2-hydroxy-3-pinanone based imines of glycine tert-butyl ester 1a or alanine isopropyl ester 1b with 1-bromo-2-fluoroethane (2) or 3-bromo-2-fluoropropene (7), respectively, followed by step-

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Section: Resultsmentioning

confidence: 97%

Stereoselective Synthesis of γ-Fluorinated α-Amino Acids Using 2-Hydroxy-3-pinanone as an Auxiliary

et al. 2000

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“…Nonlinear effects were first quantified by Kagan and coworkers and have since become a valuable tool in the study of reaction mechanisms (54)(55)(56)(57). The presence of nonlinear effects was investigated in the asymmetric ring-opening reactions with methanol as the nucleophile.…”

Section: Catalyst Studiesmentioning

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.

100

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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 ...

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“…Since 1986, many examples of NLE have been discovered in a wide variety of reactions mostly for organometallic catalysts. Some reviews have been published [25][26][27][28][29][30]. Asymmetric amplification has been specifically reviewed in references [18,29].…”

Section: Enantioimpure Auxiliaries In Asymmetric Catalysismentioning

confidence: 99%

Nonlinear Effects in Enantioselective Organometallic Catalysis

Kagan

2007

Oil & Gas Science and Technology - Rev. IFP

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*Dedicated to Yves Chauvin for his outstanding contributions to catalysis Ce manuscrit est dédié à Yves Chauvin pour ses contributions exceptionnelles à la catalyse Résumé -Effets nonlinéaires dans la catalyse organométallique énantiosélective -L'historique de la catalyse organométallique énantiosélective est rappelé en introduction. Les problèmes liés à l'emploi d'auxiliaires chiraux énantioimpurs sont discutés, les effets nonlinéaires sont définis et des modèles mathématiques simples sont présentés. De nombreux exemples d'effets nonlinéaires positifs ou négatifs sont maintenant connus, certains sont mentionnés. Les effets nonlinéaires sont utiles pour aborder des mécanismes réactionnels. L'amplification asymétrique peut avoir des applications en catalyse, en permettant d'utiliser un ligand qui n'est pas énantiopur. Abstract -Nonlinear Effects in Enantioselective Organometallic

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Nonlinear stereochemical effects in asymmetric reactions

Cited by 164 publications

References 79 publications

Stereoselective Synthesis of γ-Fluorinated α-Amino Acids Using 2-Hydroxy-3-pinanone as an Auxiliary

Stereoselective Synthesis of γ-Fluorinated α-Amino Acids Using 2-Hydroxy-3-pinanone as an Auxiliary

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

Nonlinear Effects in Enantioselective Organometallic Catalysis

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