Oxidized g-C3N4 displays very good catalytic performances in the generation of 1O2 under photochemical conditions. The hetero-Diels–Alder and ene reactions were conducted on a variety of dienes and alkenes showing a general ability of oxidized g-C3N4 to promote chemoselective and unselective oxidative processes in strong dependence from the substrates. The results offer a good panorama of the ability of this type of catalysts to be employed in organic reactions to prepare valuable synthons that can be used in several value-added preparations. A fine-tuning of the oxidative properties through further investigations on the synthesis of suitably modified g-C3N4 will be of great importance in determining a sustainable change in the approach to 1O2 generation methods, allowing for greener ways to perform organic reactions.