A green and efficient photo-induced radical addition–translocation–cyclization (RATC) reaction of terminal alkynes and α-oxocarboxylic acids has been developed. Without the addition of any external catalyst or oxidant, this method provides a novel and mild approach for the synthesis of diverse multi-functionalized cyclopentane scaffolds in good to excellent yields. Importantly, water is utilized as the reaction medium. Moreover, a mechanistic hypothesis involving a vinyl radical-mediated 1,5-HAT/cyclization is also presented.