E163-03-5 - Forschungsgruppe Nachhaltige organische Synthese und Katalyse
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Date (published):
29-Aug-2022
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Event name:
8thEuChemS Chemistry Congress
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Event date:
28-Aug-2022 - 1-Sep-2022
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Event place:
Lisbon, Portugal
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Keywords:
catalysis; asymmetric; Organocatalysis
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Abstract:
In light of the growing awareness for safe and sustainable strategies, asymmetric organocatalysis is of special interest. As metal-free catalytic reactions, these transformations feature great air– and moisture tolerance, providing a convenient and robust access to enantioenriched products. Pioneered by B. List, the field of BINOL-derived chiral phosphoric acids (CPAs) emerged to be an indispensable organocatalytic tool, providing elegant examples for the β-functionalization of enals and enones using enantiomerically pure, chiral phosphoric acids via Asymmetric Counteranion Directed Catalysis (ACDC) [1,2] Despite the remarkable advances on this field, lot of the existing methods suffer either from multi-step and tedious catalyst synthesis and/or from the difficult catalyst tunability for obtaining both product enantiomers.
As a conceptual spin-off of ACDC, we designed novel chiral frameworks composing of natural-derived chiral diamines and sterically demanding, yet flexible phosphoric acids. Such catalysts could be prepared through a straightforward parallel synthetic strategy, enabling a rather simple parameter tailoring. The optimization of the catalyst components led to the identification of a particularly powerful organocatalyst, which could be successfully applied in asymmetric epoxidations, aziridinations, as well as in two different Michael-addition-initiated cyclizations. Excellent stereocontrol was observed for all four different reactions; moreover, a simple change of the amine’s configuration provided an easy access to both product antipodes in all cases.
Based on extensive NMR studies we found, that our phosphoric acids are eventually too flexible to form stable diastereomers in chiral environment under ambient conditions, and therefore they might behave as single stereoisomeric catalysts. This could be an important aspect for avoiding the generation of matched-mismatched scenarios as a key point for achieving similarly high enantioselectivities when aiming for the opposite product antipodes.
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Project (external):
European Unions Horizon 2020
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Project ID:
D163035-1002
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Additional information:
As a conceptual spin-off of ACDC, we designed novel chiral frameworks composing of natural-derived chiral diamines and sterically demanding, yet flexible phosphoric acids. Such catalysts could be prepared through a straightforward parallel synthetic strategy, enabling a rather simple parameter tailoring. The optimization of the catalyst components led to the identification of a particularly powerful organocatalyst, which could be successfully applied in asymmetric epoxidations, aziridinations, as well as in two different Michael-addition-initiated cyclizations. Excellent stereocontrol was observed for all four different reactions; moreover, a simple change of the amine’s configuration provided an easy access to both product antipodes in all cases.
Based on extensive NMR studies we found, that our phosphoric acids are eventually too flexible to form stable diastereomers in chiral environment under ambient conditions, and therefore they might behave as single stereoisomeric catalysts. This could be an important aspect for avoiding the generation of matched-mismatched scenarios as a key point for achieving similarly high enantioselectivities when aiming for the opposite product antipodes.