Formal Giese addition of C(sp³)–H nucleophiles enabled by visible light mediated Ni catalysis of triplet enone diradicals

Abstract

Formal Giese addition of C(sp3)–H substrates is achieved by the unprecedented merger of triplet chemistry and Ni catalysis.

Hydrogen Atom Transfer Reactions via Photoredox Catalyzed Chlorine Atom Generation

“…Several alkene types may undergo background activation through triplet-triplet energy transfer processes and was elegantly demonstrated in Hongs recent study (3-PF 6 , k q cyclohexenone = 3.2 10 8 m À1 s À1 ). [12] Quenching of 2 a was found to be slower than chloride in our study (3-PF 6 , k q 2a= 6.3 AE 0.7 10 5 m À1 s À1 ; 3-Cl, k q 2a= 7.0 AE 1.6 10 5 m À1 s À1 ) and may explain why maleates and fumarates are tolerated under the described conditions. Upon generation of the electrophilic chlorine atom, complexation to a solvent such as pyridine may take place (Pyr-Cl), where the chlorine atom can undergo HAT with a variety of substrates, giving nucleophilic alkyl radical I.…”

Hydrogen Atom Transfer Reactions via Photoredox Catalyzed Chlorine Atom Generation

“…Stern–Volmer fluorescence quenching experiments found this process to be feasible when considering kinetics ( 3‐PF 6 , k q TBACl =1.1±0.1×10 6 m −1 s −1 ; 3‐Cl , k q TBACl =8.2±0.9×10 5 m −1 s −1 ). Several alkene types may undergo background activation through triplet–triplet energy transfer processes and was elegantly demonstrated in Hong's recent study ( 3‐PF 6 , k q cyclohexenone =3.2×10 8 m −1 s −1 ) . Quenching of 2 a was found to be slower than chloride in our study ( 3‐PF 6 , k q 2a= 6.3±0.7×10 5 m −1 s −1 ; 3‐Cl , k q 2a= 7.0±1.6×10 5 m −1 s −1 ) and may explain why maleates and fumarates are tolerated under the described conditions.…”

Recent advances in photoredox and nickel dual-catalyzed cascade reactions: pushing the boundaries of complexity

“…Alkyltrifluoroborates, 4m , 5 alkylsilicates, 4l , 6 carboxylic acids, 4n , 7 alkyl oxalates, 8 4-alkyl-1,4-dihydropyridines (DHPs), 4e , 9 and THF 10 have been demonstrated as readily available carbon radical precursors in photochemistry. Using photoredox and nickel dual-catalyzed cascade reactions as a platform, a series of protocols for the difunctionalization of alkynes and alkenes have been established using these radical precursors.…”