Structure and enantiomerization of helically twisted lactone-bridged biaryls: A theoretical study

Bringmann, Gerhard; Busse, H; Dauer, Ulrich; Güssregen, Stefan; Ståhl, Martin

doi:10.1016/0040-4020(95)00088-p

Cited by 32 publications

(17 citation statements)

References 16 publications

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“…nonplanar) transition states in which the bonds to the ortho substituents and the aryl rings are distorted, thus permitting the substituents to pass each other more easily than in a rigid planar transition state 41. 43–45 In many cases, the barrier to rotation can be rationalized in terms of substituent effects.…”

Section: Preconditions For Axial Chirality and Mechanisms Of Atropmentioning

confidence: 99%

Atroposelective Synthesis of Axially Chiral Biaryl Compounds

et al. 2005

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A rotationally hindered and thus stereogenic biaryl axis is the structurally and stereochemically decisive element of a steadily growing number of natural products, chiral auxiliaries, and catalysts. Thus, it is not surprising that significant advances have been made in the asymmetric synthesis of axially chiral biaryl compounds over the past decade. In addition to the classic approach (direct stereoselective aryl-aryl coupling), innovative concepts have been developed in which the asymmetric information is introduced into a preformed, but achiral-that is, symmetric or configurationally labile-biaryl compound, or in which an aryl--C single bond is stereoselectively transformed into an axis. This Review classifies these strategies according to their underlying concepts and critically evaluates their scope and limitations with reference to selected model reactions and applications. Furthermore, the preconditions required for the existence of axial chirality in biaryl compounds are discussed.

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Section: Preconditions For Axial Chirality and Mechanisms Of Atropmentioning

confidence: 99%

Atroposelective Synthesis of Axially Chiral Biaryl Compounds

et al. 2005

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“…h. thermische -Rotation um die Biarylachse über verdrillte, also nichtplanare Übergangszustände verläuft, in denen die Bindungen zu den ortho-Substituenten und die Arylringe verdreht sind, wodurch sich die Substituenten viel leichter aneinander vorbei bewegen können als in einem starren planaren Übergangszustand. [41,[43][44][45] In vielen Fällen kann die Rotationsbarriere durch Substituenteneffekte erklärt werden.…”

Section: Atropisomerisierung Durch Physikalische Rotationunclassified

“…[59] Die Gegenwart eines sechsgliedrigen Rings erleichtert noch immer merklich die Rotation, wenn auch in einem geringeren Ausmaß. Eine Vergleichsstudie an den Benzonaphthopyranonen 32 und 33 (Abbildung 7), die als racemische Gemische ihrer helical verdrillten Atrop-Enantiomere (M)-und (P)-32 und -33 (Torsionswinkel von 268 für 33 a bis 368 für 33 f) vorliegen, [45,60,61] zeigte, dass DG°2 98 K mit der Größe des ortho-Substituenten R steigt. [62] Somit atropisomerisieren 32 a-d (R = H, OMe, Me, Et) schnell bei Raumtemperatur mit Halbwertszeiten t 298 K < 1 min, während sich das Lacton 32 e (R = iPr) knapp über der Schwelle zur Atropisomerie (t 298 K = 28 min) befindet.…”

Section: Verbrückte Biaryleunclassified

Atropselektive Synthese axial‐chiraler Biaryle

et al. 2005

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Eine rotationsgehinderte und dadurch stereogene Biarylachse ist das strukturell und stereochemisch entscheidende Element einer ständig wachsenden Zahl von Naturstoffen, chiralen Auxiliaren und Katalysatoren. Daher ist es nicht überraschend, dass im letzten Jahrzehnt bedeutende Fortschritte in der asymmetrischen Synthese axial‐chiraler Biaryle erzielt worden sind. Neben dem klassischen Zugangsweg, der direkten Aryl‐Aryl‐Kupplung, sind innovative Konzepte entwickelt worden, in denen die asymmetrische Information in ein schon vorhandenes, aber nicht optisch aktives – symmetrisches oder konfigurativ labiles – Biaryl eingeführt oder eine Aryl‐C‐Einfachbindung stereoselektiv in eine Achse umgewandelt wird. In diesem Aufsatz werden die Strategien nach den zugrunde liegenden Konzepten klassifiziert, und ihre Anwendungsbreite und ihre Beschränkungen werden anhand ausgewählter Beispiele kritisch beurteilt. Ferner werden die Voraussetzungen für das Auftreten von Axialchiralität diskutiert.

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“…Detailed structural investigations on a broad series of differently substituted lactones of type by semiempirical (AM1, PM3, MNDO) 61-64 and ab initio (HF and DF, with various basis sets) 61,65 calculations show that these bridged biaryls are not flat at all (not even for D, i.e. R = H), but helically distorted and hence chiral.…”

Section: Tpurrã(mentioning

confidence: 99%

“…Indeed, quantum chemical calculations (AM1, PM3, HF) 61,69 show that the lactones enantiomerize rapidly, with isomerization barriers ranging from (as yet) unmeasurably low (20 kJ/mol) for R = H via ca. 50 and 75 kJ/mol for R = OMe and Me, respectively, up to configurational stability (ca.…”

Section: Avtrã%mentioning

confidence: 99%

The Lactone Concept: An Efficient Pathway to Axially Chiral Natural Products and Useful Reagents

1999

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$EVWUDFW A highly efficient concept for the stereoselective synthesis of axially chiral biaryl target molecules is presented: the atroposelective ring cleavage of configurationally unstable lactonebridged biaryls. The method has almost no restrictions concerning the substitution pattern, works even for substrates with high steric hindrance at the RUWKR-position(s) of the axis, and allows the optional, atropo-divergent preparation of each atropisomer from the same biaryl lactone precursor and a recycling of the undesired minor product in the sense of a chiral economy. A broad series of successful applications in natural product and ligand syntheses underlines the high value of the method. .H\ ZRUGV axial chirality, biaryl natural products, biaryl ligands and reagents, atropo-divergent synthesis, lactone-bridged biaryls '-BINAP' () R 7

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Structure and enantiomerization of helically twisted lactone-bridged biaryls: A theoretical study

Cited by 32 publications

References 16 publications

Atroposelective Synthesis of Axially Chiral Biaryl Compounds

Atroposelective Synthesis of Axially Chiral Biaryl Compounds

Atropselektive Synthese axial‐chiraler Biaryle

The Lactone Concept: An Efficient Pathway to Axially Chiral Natural Products and Useful Reagents

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