Substituent Effects on the Iodine-Catalyzed Thermal Cyclization of 3,4-Diphenylbuta-1,3-dienyl Isocyanates: Mechanistic Studies

The thermal cyclization of 3,4-diphenylbuta-1,3-dienyl isocyanates 1, generated in situ from the corresponding azides, was investigated using iodine as a catalyst. Diphenylpyridinones 2, phenylnaphthalenes 3, and indenes 4 were produced via intramolecular ring closure. The nature of the substituents on the phenyl rings was found to be crucial to the distribution of cyclized products 2–4. The mechanism of the reaction is also discussed.