Merging Photochemical Olefin Metathesis with an Amination Reaction

A merger
of photochemical olefin metathesis and C–H amination
enables us to unlock a rare protocol for the synthesis of functionalized
olefins. Our method allows for the stereoselective generation of enamines
using a mild and bench-stable oxime ester precursor as the N-linchpin.
The key feature is the multitasking catalysis of fac-Ir(ppy)3, which not only enables the energy transfer
(EnT) mediated N–O bond cleavage of an oxime ester to produce
an N-centered radical (NCR) and a benzoyloxy radical (•OBz) but also promotes the cycloaddition of two styrene moieties
to form a cyclobutane analogue at different stages of the reaction.
Further, mechanistic investigations and DFT calculations provide crucial
insights on a rare ring-opening metathesis, prompted by the oxidation
of the cyclobutane intermediate, followed by nucleophilic attack of
an in situ generated benzoate anion (−OBz) and radical-coupling with NCR leading to a highly stable singlet
intermediate that undergoes sequential N-protonation
and single electron reduction to effectuate elimination and regeneration
of •OBz, delivering the Z-selective
aminated stilbene. Reasonable functionality tolerance, in addition
to satisfactory yield and exclusive stereoselectivity are the salient
features of this newly discovered methodology.