Addition and Cyclization Reactions in the Thermal Conversion of Hydrocarbons with an Enyne Structure, 4. Formation and Rearrangements of Bicyclic C10H8 Aromatics from 1‐Phenyl‐1‐buten‐3‐yne

The thermal conversion of 1-phenyl-1-buten-3-yne (1) into the cycloisomerization products naphthalene (2), azulene (3), and 1-methylene-1H-indene (4) has been studied at temperatures between 550 and 1000°C, a reaction time of approximately 0.3 s at 13 Torr (FVP) and at low partial pressures in a quartz flow system. The results obtained by FVP as well as in the presence of chemically modified diluent gases suggest a predominance of unimolecular cycloisomerizations to 2 and 3 which are, however, always accompanied by radical cyclization reactions to 2 and 4 even under FVP conditions if temperatures above 550°C are applied.