Thermal Rearrangements, XXV. The Automerization of Benzene as A Radical-Initiated Reaction

✍ Scribed by Zimmermann, Gerhard ;Nüchter, Matthias ;Hopf, Henning ;Ibrom, Kerstin ;Ernst, Ludger

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 526 KB
• Volume: 1996
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.199619960911

✦ Synopsis

Abstract

The thermal isomerization of [1,4‐D~2~]‐ (3a) and [1,2‐^13^C~2~]benzene (1a) has been studied in excess hydrogen at 750–850°C with contact time less than 1.2 s and very low partial pressure in a quartz flow system. In both cases, the main isomerization products are the corresponding meta isomers. The data suggest a radical intramolecular interchange of the benzene carbon atoms by 1,2‐C shifts. The multistep reaction cascade is initiated by H addition to the benzene ring followed by transannular homoallyl rearrangements involving the intermediate formation of bicyclo[3.1.0]hexenyl and cyclopentadienylmethyl radicals. This pathway constitutes a side reaction competing with the direct stabilization of the cyclohexadienyl radicals formed preferentially at high temperature.