Enantioselective Hydroamination of Alkenes with Sulfonamides Enabled by Proton-Coupled Electron Transfer

An
enantioselective, radical-based method for the intramolecular
hydroamination of alkenes with sulfonamides is reported. These reactions
are proposed to proceed via N-centered radicals formed
by proton-coupled electron transfer (PCET) activation of sulfonamide
N–H bonds. Noncovalent interactions between the neutral sulfonamidyl
radical and a chiral phosphoric acid generated in the PCET event are
hypothesized to serve as the basis for asymmetric induction in a subsequent
C–N bond forming step, achieving selectivities of up to 98:2
er. These results offer further support for the ability of noncovalent
interactions to enforce stereoselectivity in reactions of transient
and highly reactive open-shell intermediates.