Ph ₃ N as an Organocatalytic Donor for Photoactivation of Pyridinium-Masked Enols in the Formal [4 + 2] Cycloaddition with Unactivated Olefins

Herein, we demonstrated that commercially available and inexpensive triphenylamine (NPh₃) could act as an electron donor to form electron donor-acceptor (EDA) complexes with pyridinium-masked enols. Upon irradiation with blue light (455 nm), this <i>in situ</i> formed EDA complex was activated to provide the α-carbonyl radical through N-O bond cleavage, serving as the radical precursor in the formal [4 + 2] cycloaddition with unactivated olefins. A series of pyridinium-masked enols and functionalized olefins were examined under optimized conditions. Mechanistic studies revealed that α-carbon radical and γ-carbonyl radical intermediates are involved during this catalytic process.