On the mechanism of formation and fragmentation of [8]paracyclophane in the gas phase

✍ Scribed by Paulus A. Kraakman; Paulus J. K. M. Eeken; Willem H. de Wolf; Friedrich Bickelhaupt

• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 831 KB
• Volume: 109
• Category: Article
• ISSN: 0165-0513
• DOI: 10.1002/recl.19901090320

✦ Synopsis

Abstract

Regiospecifically labelled 3‐[(^13^C)methylene]spiro[5.7]trideca‐1,4‐diene (2a′) and (1‐^13^C)‐dispiro[2.2.6.2] tetradeca‐4,13‐diene (7a′) were prepared. By flash vacuum thermolysis (FVT) at 600°C, 2a′ was converted into [8]paracyclophane (1a′) in 95% yield. The label in 1a′ was found at the benzylic position(s). At 750°C, 1a′ fragmented by cleavage of the homobenzylic bonds finally yielding (after extrusion of one or more molecules of propene or ethene) p‐ethyl‐ (4e′) and p‐propyl‐(4d′) styrene. The styrenes were labelled at both benzylic carbon atoms. The product spectrum obtained by FVT of 7a′ was more complex. At 600°C, 1a′, 7a′ and 3‐ vinylspiro[5.6]undeca‐4,13‐diene (11a′) were found. Compound 1a′ was labelled at both the benzylic and homobenzylic positions, whereas 11a′ was labelled only at the two carbon atoms of the vinyl group. At 750 °C, the p‐(n‐alkyl)styrenes 4a′, 4d′ and 4e′, the p‐(sec‐alkyl)styrenes 14d′ and 14e′ and p‐divinylbenzene (15′) were found. Compound 4a′ was labelled only on both carbon atoms of the vinyl group, 4d′ and 4e′ also at the benzylic carbon atom of the alkyl group and 4e′ at the terminal methyl group. The p‐(sec‐alkyl)styrenes 14d′ and 14e′ were labelled exclusively at the benzylic carbon atom and the sec‐methyl group of the sec‐alkyl chain. The distribution of the label in the pyrolysis products is in line with the previously suggested routes for their formation. A full explanation for the (low‐percentage) incorporation of label at some unexpected positions will only be available after further investigation.