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Concerted Catalysis by Nanocellulose and Proline in Organocatalytic Michael Additions.

ABSTRACT: Cellulose nanofibers (CNFs) have recently attracted much attention as catalysts in various reactions. Organocatalysts have emerged as sustainable alternatives to metal-based catalysts in green organic synthesis, with concerted systems containing CNFs that are expected to provide next-generation catalysis. Herein, for the first time, we report that a representative organocatalyst comprising an unexpected combination of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-oxidized CNFs and proline shows significantly enhanced catalytic activity in an asymmetric Michael addition.

SUBMITTER: Ranaivoarimanana NJ

PROVIDER: S-EPMC6480416 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature

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Enantioselective desymmetrization of prochiral cyclohexanones by organocatalytic intramolecular Michael additions to α,β-unsaturated esters.

Project description:A new catalytic asymmetric desymmetrization reaction for the synthesis of enantioenriched derivatives of 2-azabicyclo[3.3.1]nonane, a key motif common to many alkaloids, has been developed. Employing a cyclohexanediamine-derived primary amine organocatalyst, a range of prochiral cyclohexanone derivatives possessing an α,β-unsaturated ester moiety linked to the 4-position afforded the bicyclic products, which possess three stereogenic centers, as single diastereoisomers in high enantioselectivity (83-99% ee) and in good yields (60-90%). Calculations revealed that stepwise C-C bond formation and proton transfer via a chair-shaped transition state dictate the exclusive endo selectivity and enabled the development of a highly enantioselective primary amine catalyst.

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Michael Additions of Highly Basic Enolates to ortho-Quinone Methides.

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