Kinetic Resolution of β-Stereogenic<i>O</i>-Alkyl Carbamates by (-)-Sparteine-Assisted Deprotonation. External versus Internal Chiral Induction.

Haller, Jan; Hense, Thomas; Hoppe, Dieter

doi:10.1055/s-1993-22585

Cited by 26 publications

(9 citation statements)

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“…The method has also been applied to N-Bocpyrrolidines, [10,11] several benzylic substrates, [12] ferrocenes, [13] P,P-dimethylarylphosphane derivatives, [14] as well as to the kinetic resolution of a racemic allyl carbamate [15] and of several b-stereogenic alkyl carbamates. [16] Moreover, a desymmetrization of meso-oxabicycles by alkyllithium/(À)-sparteine-induced ring-opening has been described by Lautens et al [17] and Hodgson et al [18] The (À)-sparteine-induced deprotonation of alkyl carbamates 3 generated from primary alcohols, which bear nonmesomerically stabilizing groups adjacent to the carbanionic center in 5, is characterized by a pronounced pro-S selectivity in the deprotonation step. The intermediates 5 are configurationally stable and the reaction with most electrophiles occurs with retention of the configuration to produce the adducts 6 (Scheme 2).…”

Section: Introductionmentioning

confidence: 97%

Efficient Desymmetrization ofmeso-cis-1,2-Cyclohexanedimethanol with Differentiation between Diastereotopic and Enantiotopic C−H Bonds by (−)-Sparteine-Mediated Deprotonation

et al. 1999

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The deprotonation of a dicarbamate prepared from cis-1,2-cyclohexanedimethanol by sec-butyllithium/(À)-sparteine proceeds with efficient selection between the enantiotopic branches and their diastereotopic protons with high preference for the pro-S proton at the R branch to afford the intermediate, configurationally stable lithium compound as a single diastereomer. Trapping of this intermediate by electrophiles (DOMe, CO 2 , CH 3 I, Me 3 SiCl, or R 3 SnCl) takes place with retention of the configuration to yield highly enantiomerically and diastereomerically enriched substitution products, which are easily converted to diols, to anellated tetrahydrofurans, or to g-lactones. The chiral base is also capable of efficient kinetic resolution of the racemic adeuterated starting material, by the utilization of an extraordinarily high kinetic H/D isotope effect within the deprotonation step. The, presumably, first example of the kinetic resolution of a racemic stannane by lithiodestannylation, utilizing methyllithium/(À)-sparteine, is reported.

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Section: Introductionmentioning

confidence: 97%

Efficient Desymmetrization ofmeso-cis-1,2-Cyclohexanedimethanol with Differentiation between Diastereotopic and Enantiotopic C−H Bonds by (−)-Sparteine-Mediated Deprotonation

et al. 1999

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“…[21] More direct routes to stereodefined carbenoids are desirable.O utstanding in this regard is the enantioselective (e.g. entry 12), [22,23] diastereoselective, [24] and stereospecific (e.g. entry 13), [25] direct deprotonation of N,N-dialkyl O-alkyl carbamates developed by the Hoppe group.…”

Section: Generation Of Stereodefined Carbenoids and Their Configuratimentioning

confidence: 99%

Formation of Olefins by Eliminative Dimerization and Eliminative Cross‐Coupling of Carbenoids: A Stereochemical Exercise

Blakemore

Hoffmann

2017

Angew Chem Int Ed

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Two carbenoids combine to generate an olefin by a mechanism involving formation of an ate complex, 1,2-metalate rearrangement, and β-elimination. As each stage of this eliminative coupling is stereospecific, the overall stereochemical outcome can be understood and, in principle fully controlled, providing that the absolute stereochemical configurations of the reacting carbenoid species are defined. In contrast to traditional alkene syntheses, the eliminative cross-coupling of carbenoids offers a connective approach to olefins capable of precisely targeting a given isomer regardless of the nature of the features distinguishing the isomers. The formation of olefins by the eliminative dimerization and eliminative cross-coupling of carbenoids is reviewed with a range of illustrative examples, including the reactions of α-lithiated haloalkanes, epoxides, and carbamates. An emphasis is placed on stereochemical analysis and methods to generate sp -hybridized carbenoids in stereodefined form are surveyed.

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“…Dabei fällt der Blick auf die enantioselektive (Nr. 12), diastereoselektive und stereospezifische (Nr. 13) direkte Deprotonierung von N , N ‐Dialkyl‐ O ‐alkylcarbamaten der Hoppe‐Gruppe .…”

Section: Erzeugung Stereodefinierter Carbenoide Und Deren Konfiguratiunclassified

Olefin‐Bildung durch eliminierende Dimerisierung und eliminierende Kreuzkupplung von Carbenoiden: eine stereochemische Herausforderung

Blakemore

Hoffmann

2017

Angewandte Chemie

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Bei der Dimerisierung von Carbenoiden entstehen Olefine, und zwar über die Bildung eines At‐Komplexes, eine nachfolgende 1,2‐Metallat‐Umlagerung und eine abschließende β‐Eliminierung. Da jeder dieser Schritte stereospezifisch ist, kann man das stereochemische Endergebnis nachvollziehen und – im Prinzip – auch steuern, vorausgesetzt, die absolute Konfiguration der reagierenden Carbenoide ist festgelegt. Eine eliminierende Kreuzkupplung zweier unterschiedlicher Carbenoide ermöglicht eine Aufbaureaktion, bei der im Unterschied zu bekannten Olefin‐Synthesen die Geometrie der Doppelbindung unabhängig von der Art der Reste an der Doppelbindung festgelegt werden kann. Die Bildung von Olefinen durch eliminierende Dimerisierung/Kreuzkupplung von Carbenoiden wird an einer Reihe von typischen Beispielen illustriert, etwa an Reaktionen von α‐lithiierten Halogenalkanen, Epoxiden und Carbamaten. Dabei gilt das Augenmerk auch der Erzeugung von sp3‐hybridisierten Carbenoiden mit definierter Konfiguration und deren stereochemischer Zuordnung.

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Kinetic Resolution of β-StereogenicO-Alkyl Carbamates by (-)-Sparteine-Assisted Deprotonation. External versus Internal Chiral Induction.

Cited by 26 publications

References 0 publications

Efficient Desymmetrization ofmeso-cis-1,2-Cyclohexanedimethanol with Differentiation between Diastereotopic and Enantiotopic C−H Bonds by (−)-Sparteine-Mediated Deprotonation

Efficient Desymmetrization ofmeso-cis-1,2-Cyclohexanedimethanol with Differentiation between Diastereotopic and Enantiotopic C−H Bonds by (−)-Sparteine-Mediated Deprotonation

Formation of Olefins by Eliminative Dimerization and Eliminative Cross‐Coupling of Carbenoids: A Stereochemical Exercise

Olefin‐Bildung durch eliminierende Dimerisierung und eliminierende Kreuzkupplung von Carbenoiden: eine stereochemische Herausforderung

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