Enantioselective Photocatalysis Using a Privileged Al-Salen Complex

Area of Science:

• Catalysis
• Photochemistry
• Organic Synthesis

Background:

• Enantioselective catalysts are crucial for synthesizing chiral molecules.
• Achieving high efficiency in excited-state catalysis remains a challenge.
• Aluminum-salen (Al-salen) complexes show promise due to their photophysical properties.

Purpose of the Study:

• To explore the potential of Al-salen complexes as photocatalysts.
• To develop new structure-activation guidelines for excited-state catalysis.
• To demonstrate Al-salen's utility in deracemization and photocyclization reactions.

Main Methods:

• Utilized commercial Al-salen complexes for photochemical transformations.
• Employed single electron transfer (SET) for deracemization of cyclopropyl ketones.
• Applied energy transfer (EnT) catalysis for enantioselective photocyclization of acrylanilides.
• Combined experimental and computational approaches for mechanistic studies.

Main Results:

• Achieved efficient deracemization of cyclopropyl ketones (up to 98:2 e.r.) via a C(sp3)-C(sp3) bond cleavage/cyclization pathway.
• Facilitated enantioselective photocyclization of acrylanilides to diverse heterocycles (up to quantitative yield and 96:4 e.r.).
• Demonstrated Al-salen as a versatile chiral operator in distinct photochemical reactions.

Conclusions:

• Light activation significantly expands the reactivity of Al-salen catalysts beyond ground-state applications.
• Photochemical strategies overcome limitations of thermochemically challenging reactions.
• This approach accelerates the discovery of chiral functional molecules.