AbstractThe photochemical synthesis of indole derivatives starting from the indoline‐2‐thiones 1 is described. Irradiation of indoline‐2‐thiones 1 in the presence of alkenes 3 gave 2‐alkyl‐3H‐indoles 4–7 or 2‐alkylindoles 8–22 through the ring cleavage of the intermediates, spirocyclic amino‐thietanes, initially derived by [2 + 2] cycloaddition of the CS bond of 1 and the CC bond of 3. Irradiation of 1 in the presence of trialkylamines 26 gave desulfurization products 27–32 and unexpected 3‐alkylindoles 33–40. N‐Acylindoline‐2‐thiones 11‐p yielded the deacylated products, indoline‐2‐thiones 1a‐b, and ethyl esters 43 through γ‐H abstraction by the excited thioamide S‐atom when irradiated in CDC13/EtOH or benzene/EtOH. Oxygen analogues 2a‐d also underwent intramolecular H abstraction to give the indolin‐2‐ones 2e–f and ethyl esters 43 in a similar way.