Generation of N-Centered Radicals via a Photocatalytic Energy Transfer: Remote Double Functionalization of Arenes Facilitated by Singlet Oxygen

An unprecedented approach for the generation of N-centered radical via a photocatalytic energy transfer process from readily available heterocyclic precursors is reported, which is distinctive to the previous electron transfer approaches. In combination with singlet oxygen, the in situ generated nitrogen radical from oxadiazoline substrate in the presence of fac-Ir(ppy)3 undergoes a selective ipso-addition to arenes to furnish remotely double functionalized spiro-azalactam products. The mechanistic studies provide compelling evidence that the catalytic cycle selects the energy transfer pathway. A concurrent activation of molecular oxygen to generate singlet oxygen by energy transfer is also rationalized. Furthermore, the occurrence of electron transfer phenomenon is excluded based on the negative driving forces for one-electron transfer between oxadiazoline and the excited state of fac-Ir(ppy)3 with consideration to their redox potentials. The necessity of singlet oxygen as well as the photoactivated oxad...