Unexpected Pyrolytic Behaviour of Substituted Benzo[c]thiopyran and Thieno[2,3-c]thiopyran S,S-dioxides

R Alan Aitken, Clémence Hauduc, M. Selim Hossain, Emily McHale, Adrian L. Schwan, Alexandra Martha Zoya Slawin, Colin A. Stewart

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6 Citations (Scopus)


Flash vacuum pyrolysis (FVP) of benzo[c]thiopyran S,S-dioxide 1 results in formation of indene and 2-vinylbenzaldehyde as previously described. A range of eight analogues with various substitution patterns are found to behave differently. In general there is no extrusion of SO2 to give products analogous to indene, but unsaturated carbonyl products analogous to 2-vinylbenzaldehyde are formed in most cases by way of ring expansion to a 7-membered ring sultine, extrusion of SO, and intramolecular hydrogen atom transfer. Other processes observed include formation of anthracene via an isomeric 7-membered sultine with loss of SO, CO and methane or butane, and formation of 4-ethylidene-4,5-dihydrocyclobuta[b]thiophenes by way of SO loss, a radical rearrangement and extrusion of acetone. The analogues with a halogen substituent at position 8 on the benzene ring require a higher temperature to react and give naphthalene resulting from net elimination of HX and SO2. The X-ray crystal structure of 1 is also reported.

Original languageEnglish
Pages (from-to)1288-1295
Number of pages8
JournalAustralian Journal of Chemistry
Issue number8/9
Early online date30 May 2014
Publication statusPublished - 2 Sept 2014


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