Visible Light-Induced Direct S0 → Tn Transition of Benzophenone Promotes C(sp3)-H Alkynylation of Ethers and Amides

Benzophenone has an S-0 -> S-1 absorption band at 365 nm. However, the rarely reported S-0 -> T-n transition occurs upon irradiation at longer wavelengths. Herein, we employed benzophenone as a catalyst and exploited its S-0 -> T-n transition in C(sp(3))-H alkynylations with hypervalent iodine reagents. The selective benzophenone excitation prevented alkynylating reagent decomposition, enabling the reaction to proceed under mild conditions. The reaction mechanism was investigated by spectroscopic and computational studies.