A new access to artemisinin is reported based on a selective photochemical hydrothiolation of amorphadiene, a waste product of the industrial semisynthetic route. This study highlights the discovery of two distinctive activation pathways under solvent-free conditions or using a photocatalyst promoting H-abstraction. Subsequently, a chemoselective oxidation of the resulting photochemically generated thioether, followed by a Pummerer rearrangement, affords dihydroartemisinic aldehyde, a key intermediate in the synthesis of artemisinin.