This review describes the discovery of new reactions in the field of heterocyclic chemistry. The reactions taken as typical examples involve 1) the photochemical ring transformations of quinolines to indole rings, 2) the ring transformations of indoles to quinazoline and quinoxaline rings, 3) the ring expansion reactions of indoles to 1H-1-benzazepines, 4) the intramolecular photo[2+2]cycloaddition reactions of 2- or 3-alkenyloxy-(or amino-)cyclohex-2-en-1-ones, 5) the syntheses of the nitrogen-containing heterocycles using the cyclizations of N-alkenylcarbamoylmethyl radicals, and 6) the general syntheses of bridged azabicyclic compounds using radical translocation/cyclization reactions. Modification of the water-soluble aminating agent hydroxylamine-O-sulfonic acid to the more powerful aminating agent O-mesitylenesulfonylhydroxylamine is also described.