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.