Catalytic Olefin Hydroamidation Enabled by Proton-Coupled Electron Transfer

Abstract

Here we report a ternary catalyst system for the intramolecular hydroamidation of unactivated olefins using simple N-aryl amide derivatives. Amide activation in these reactions occurs via concerted proton-coupled electron transfer (PCET) mediated by an excited state iridium complex and weak phosphate base to furnish a reactive amidyl radical that readily adds to pendant alkenes. A series of H-atom, electron, and proton transfer events with a thiophenol cocatalyst furnish the product and regenerate the active forms of the photocatalyst and base. Mechanistic studies indicate that the amide substrate can be selectively homolyzed via PCET in the presence of the thiophenol, despite a large difference in bond dissociation free energies between these functional groups.

Light on Unsaturated Hydrocarbons – “Gotta Heterofunctionalize Them All”

“…Com- Scheme 5. The hydroamidation of benzamide derivatives reported by Chen. pared to those in their previous work, [17] the hydrazones can be substituted differently on the phenylsulfonyl ring (23). Aromatic and alkyl hydrazones were well tolerated, as shown in examples 20, 21, and 22.…”

Photoredox Catalysis in Organic Chemistry

“…This radical can then either be trapped by a Michael acceptor, yielding the product of net carboamination of the alkene, 60 or undergo a hydrogen atom transfer event with thiophenol, thereby furnishing the hydroamination product. 61 …”

Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

“…Looking to expand on these results and develop further olefin amidofunctionalization reactions, we questioned if we could identify a suitable hydrogen-atom donor reagent capable of furnishing a hydroamidation product, as illustrated in Figure 30 [222]. Based on this catalytic cycle, we anticipated such a donor would ideally enable facile HAT to the cyclized radical alkyl species, as wel as a R•/R − redox couple suitable to oxidize the reduced state of the photocatalyst, resulting in the formation of an anion basic enough to deprotonate the phosphoric acid generated during the initial PCET event.…”