A surprising switch from the Myers-Saito cyclization to a novel biradical cyclization in enyne-allenes: Formal Diels-Alder and ene reactions with high synthetic potential

If there is an aryl substituent on the acetylene terminus of enyne - allenes, then its reaction mode may be changed from the Myers - Saito cyclization to a novel C2-C6 cyclization resulting in a net intramolecular Diels-Alder or ene reaction. As a consequence, the thermal cyclization of readily accessible acyclic enyne-allenes can be utilized for the synthesis of complex benzofulvene and benzofluorene derivatives. Kinetic results of the C2-C6 cyclization reaction indicate a two-step reaction pathway with a benzofulvene biradical intermediate.