Iron-Catalyzed Photoinduced LMCT: A 1° C-H Abstraction Enables Skeletal Rearrangements and C(sp3)-H Alkylation

Herein we disclose an iron-catalyzed method to access skeletal rearrangement reactions akin to the Dowd-Beckwith ring expansion from unactivated C(sp(3))-H bonds. Photoinduced ligand-to-metal charge transfer at the iron center generates a chlorine radical, which abstracts electron-rich C(sp(3))-H bonds. The resulting unstable alkyl radicals can undergo rearrangement in the presence of suitable functionality. Addition to an electron deficient olefin, recombination with a photoreduced iron complex, and subsequent protodemetalation allow for redox-neutral alkylation of the resulting radical. Simple adjustments to the reaction conditions enable the selective synthesis of the directly alkylated or the rearranged-alkylated products. As a radical clock, these rearrangements also enable the measurement of rate constants of addition into various electron deficient olefins in the Giese reaction.

Automated summary

In this study, an iron-catalyzed method was developed for skeletal rearrangement reactions from unactivated C(sp(3))-H bonds to access alkylated products. By utilizing photoinduced ligand-to-metal charge transfer, a chlorine radical is generated at the iron center to abstract electron-rich C(sp(3))-H bonds, leading to the formation and rearrangement of alkyl radicals for the synthesis of alkylated products. Simple adjustments to the reaction conditions enable the selective synthesis of directly alkylated or rearranged-alkylated products.