Intramolecular radical substitution reactions: a novel approach to fused [1,2-a] indoles

A new approach to fused [1,2-a]indoles 25, 26 and 27 is described; the synthesis is based on a novel intramolecular radical cyclization reaction involving ipso-substitution using sulfone, sulfide and sulfoxide substituted indoles. Some more general aspects of scope and limitation of the process are presented including vinyl and aryl radical cyclizations of 29 and 30; investigations using substituted indoline and aniline derivatives 35 and 37 are also discussed.