Addition and Cyclization Reactions in the Thermal Conversion of Hydrocarbons with an Enyne Structure, 5. High-Temperature Ring Closures of 1,3-Hexadien-5-ynes to Naphthalenes – Competing Reactions via Isoaromatics, Alkenylidene Carbenes, and Vinyl-type Radicals

✍ Scribed by Hofmann, Jörg ;Schulz, Kathrin ;Altmann, Annett ;Findeisen, Matthias ;Zimmermann, Gerhard

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 761 KB
• Volume: 1997
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.199719971218

✦ Synopsis

Abstract

The 4‐substituted 1‐phenyl‐1‐butene‐3‐ynes 1a–c and the 2‐ethynylstyrenes 7a–c were subjected to high‐temperature pyrolysis. The cycloisomerization products isolated suggest that these are formed by three competing processes: by (i) an electrocyclic or a molecule‐induced, (ii) an alkenylidene carbene controlled, and (iii) a radical‐controlled ring‐closure process. To estimate the relative importance of these three reactions here mentioned, the substrates have been isomerized in oxygen‐free nitrogen and in nitrogen proportionally substituted by toluene at 700 and 650 °C, respectively. The relative contributions of these isomerizations depend not only on the conversion temperature but also on the substitutent R in 1 or 7.