Dual C(sp 3 )–H Functionalization of Cyclic Ethers via Singlet Oxygen-Mediated Ring Opening and Ring Closing

A metal-free dual C(sp 3 )–H bond functionalization of saturated cyclic ethers via photooxidative singlet oxygen-mediated ring opening and ring closing has been developed, providing a method for generating hydrobenzofurans/pyrans/dioxins. Mechanistic studies have confirmed that ring-opening intermediates were effectively generated by singlet oxygen-mediated C(sp 3 )–H activation and efficiently reacted with aldehydes and activated methylene compounds to form a wide array of products with high diastereoselectivities (up to >95:5 dr). This study is a rare example of α,β-dual C(sp 3 )–H bond functionalization of ethers.