Highly selective asymmetric hydrogenation using a three hindered quadrant bisphosphine rhodium catalyst

Area of Science:

• Organic Chemistry
• Asymmetric Catalysis
• Medicinal Chemistry

Background:

• Chiral ligands and metal complexes are crucial for enantioselective synthesis.
• Rhodium catalysts are widely used in asymmetric hydrogenation reactions.
• Efficient synthesis of enantiomerically pure compounds is vital for pharmaceuticals.

Purpose of the Study:

• To synthesize both enantiomers of a novel rhodium complex (5).
• To evaluate the enantioselectivity of rhodium complex 5 in asymmetric hydrogenation.
• To compare the efficacy of catalyst 5a with Rh-Me-DuPhos for large-scale synthesis.

Main Methods:

• Synthesis of ligand 2 and rhodium complex 5.
• Chiral High-Performance Liquid Chromatography (HPLC) for enantiomeric separation.
• Asymmetric hydrogenation of alpha-acetamido dehydroamino acids (6a-e) and pregabalin precursor (8).

Main Results:

• Successful synthesis of both enantiomers of ligand 2 and rhodium complex 5.
• Rhodium complex 5 demonstrated high enantioselectivity (>99% ee) in hydrogenation reactions.
• Catalyst 5a showed advantages over Rh-Me-DuPhos for large-scale hydrogenation of precursor 8.

Conclusions:

• The novel rhodium complex 5, featuring hindered quadrants, achieves excellent enantioselectivity.
• This catalyst is effective for the asymmetric hydrogenation of amino acid derivatives and pharmaceutical precursors.
• Catalyst 5a presents a promising alternative for industrial-scale asymmetric hydrogenation.