Iridium-Catalyzed Enantioselective Intermolecular Indole C2-Allylation

Area of Science:

• Organic Chemistry
• Catalysis
• Asymmetric Synthesis

Background:

• Indole derivatives are crucial scaffolds in medicinal chemistry and materials science.
• Direct C-H functionalization of indoles offers efficient synthetic pathways.
• Achieving regioselective C2-functionalization of 3-substituted indoles remains challenging.

Purpose of the Study:

• To develop a novel enantioselective intermolecular C2-allylation of 3-substituted indoles.
• To establish a directing group-free catalytic system for this transformation.
• To elucidate the mechanism and factors governing C2-selectivity.

Main Methods:

• Utilized a chiral iridium-(P, olefin) complex as the catalyst.
• Employed Mg(ClO4)2 as a Lewis acid co-catalyst.
• Investigated reaction conditions and substrate scope.
• Performed experimental studies and Density Functional Theory (DFT) calculations.

Main Results:

• Achieved the first reported enantioselective intermolecular C2-allylation of 3-substituted indoles.
• Obtained C2-allylated products in high yields (40-99%) and enantioselectivities (83-99% ee).
• Demonstrated excellent regiocontrol, favoring C2 over C3 allylation.
• DFT calculations and experimental evidence support a direct C2-allylation mechanism.

Conclusions:

• The developed method provides an efficient and selective route to C2-allylated indoles.
• Steric hindrance at the C3 position and π-π stacking interactions are key to C2-selectivity.
• This work expands the toolbox for asymmetric synthesis of functionalized indoles.