Photocatalyst-Free 1,2- <i>vic</i> Elimination toward the Synthesis of 4,6- <i>O</i> -Protected Glycals under Visible Light

A photocatalyst-free vicinal elimination of 1,2-functionalized pyranoses has been developed using a mild base such as triethylamine (Et₃N). This method enables the synthesis of synthetically challenging 4,6-<i>O</i>-protected unsaturated sugars from readily accessible 2-deoxy-2-haloglycopyranosyl azides. The reaction proceeds under blue LED irradiation via the formation of an electron donor-acceptor (EDA) complex, as confirmed by UV-vis spectroscopy. Controlled experiments confirm that the presence of both azide and halogen is essential for the vicinal elimination, irrespective of their relative position and stereochemistry.