Temperature-controlled bidirectional enantioselectivity in a dynamic catalyst for asymmetric hydrogenation

Area of Science:

• Organic Chemistry
• Catalysis
• Stereochemistry

Background:

• Asymmetric catalysis is crucial for synthesizing enantiomerically pure compounds.
• Current methods often require separate catalysts or complex chiral separations.
• Developing single catalysts with tunable selectivity is highly desirable.

Purpose of the Study:

• To develop a stereochemically flexible catalyst for asymmetric hydrogenation.
• To achieve temperature-dependent enantioselectivity using a single catalyst system.
• To efficiently produce both enantiomers of target compounds.

Main Methods:

• Utilized a diastereomeric rhodium(I) complex as an axially chiral catalyst.
• Performed asymmetric hydrogenation reactions on prochiral (Z)-α-acetamidocinnamates and α-substituted acrylates.
• Manipulated reaction temperature to control catalyst enantioselectivity.

Main Results:

• The rhodium(I) catalyst demonstrated temperature-dependent enantioselectivity.
• High yields and enantioselectivities were achieved for both (R)- and (S)-enantiomers.
• Low temperatures favored (R)-phenylalanine derivatives (up to 87:13 R/S).
• Elevated temperatures favored (S)-enantiomers (up to 3:97 R/S) after catalyst re-equilibration.

Conclusions:

• A single, stereochemically flexible rhodium(I) catalyst enables the synthesis of both enantiomers.
• Temperature control offers a simple and effective strategy to switch enantioselectivity.
• This approach streamlines the preparation of enantiomerically pure compounds, reducing synthetic complexity.