THERMOLYSIS OF [1-13C]-2-METHYLAZULENE AND MECHANISM OF THE AZULENE TO NAPHTHALENE REARRANGEMENT

Thermolysis of [1-13C]-2-methylazulene gives 1-methylnaphthalene (1-MN) labeled at C-2, C-3, C-9, and C-10 and 2-methylnaphthalene (2-MN) labeled at C-1, C-3, and C-4. To account for these and previous results, it is proposed that the rearrangement of azulene to naphthalene at 440 °C proceeds by two competing mechanisms (the methylene walk and spiran pathways), both of them sequences of homoallyl-cyclopropylcarbinyl steps in azulene radical adducts. The spiran pathway, however, also involves hydrogen shifts. © 1979, American Chemical Society. All rights reserved.