Photoredox Iridium Catalyst for Single Electron Transfer (SET) Cross-Coupling
Photoredox Iridium Catalyst for Single Electron Transfer (SET) Cross-Coupling
INTRODUCTION
C(sp²)- and C(sp)-hybridized coupling reactions are established catalytic approaches. However, multi-step C(sp³)- and C(sp²)-coupling reactions of boronic acids and related derivatives are still limited by ineffective two-electron transmetalation reactions. These conventional protocols exhibit reactivity profiles related to heterocyclic C-B bond strengths, thereby greatly impeding progress toward efficient cross-coupling of C(sp³)-hybridized alkylboron nucleophiles.
Recently, a series of efficient, single-election transmetalation methods have been optimized for alkyl cross-coupling using a dual-catalyst system of nickel (B115561) and iridium (B283112) catalysts, whereby a potassium organotrifluoroborate is activated for cross-coupling via oxidative fragmentation to an alkyl radical. This mechanistic paradigm allows reactivity to be dictated by homolytic bond strengths, opening a new realm of possibilities in alkylboron cross-coupling. In collaboration with the expertise in this field, we now offer a novel catalyst for high-yielding SET reactions.
ADVANTAGES
•Previously unrealistic C(sp³)-coupling reactions are now an efficient reality
•Reaction is performed at room temperature
•Possibilities for asymmetric coupling
•Reductive elimination using a chiral nickel catalyst allows stereoconvergent synthesis from racemic organotrifluoroborate substrates
References
1. Tellis JC, Primer DN, Molander GA. 2014. Single-electron transmetalation in organoboron cross-coupling by photoredox/nickel dual catalysis. Science. 345(6195):433-436. https://doi.org/10.1126/science.1253647
2. Primer DN, Karakaya I, Tellis JC, Molander GA. 2015. Single-Electron Transmetalation: An Enabling Technology for Secondary Alkylboron Cross-Coupling. J. Am. Chem. Soc.. 137(6):2195-2198. https://doi.org/10.1021/ja512946e
3. Gutierrez O, Tellis JC, Primer DN, Molander GA, Kozlowski MC. 2015. Nickel-Catalyzed Cross-Coupling of Photoredox-Generated Radicals: Uncovering a General Manifold for Stereoconvergence in Nickel-Catalyzed Cross-Couplings. J. Am. Chem. Soc.. 137(15):4896-4899. https://doi.org/10.1021/ja513079r
4. Karakaya I, Primer DN, Molander GA. 2015. Photoredox Cross-Coupling: Ir/Ni Dual Catalysis for the Synthesis of Benzylic Ethers. Org. Lett.. 17(13):3294-3297. https://doi.org/10.1021/acs.orglett.5b01463