A selenium radical triggered switchable ortho/ipso-cyclization cascade of N-aryl alkynamides has been devised under metal-free conditions to access 3-selenyl quinolin-2-ones and 3-selenospiro[4,5]trienones in high yields (up to 98%). The simple protocol is scalable and the mechanistic studies suggest that the radical cascade proceeds through a spirocyclic intermediate which is formed via an intramolecular ipso-cyclization route. © 2019 The Royal Society of Chemistry.