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Abstract
The flash vacuum thermolysis (FVT) of the tricyclic sulfides 2 and 4 led, upon elimination of cyclopentadiene by retro-Diels-Alder reaction, to a mixture of isomeric allylthio- or propargylthiocyclopentadienes (12, 13 and 16, 17, respectively). Compounds 13 and 17 underwent in turn a thio-Claisen rearrangement giving the reactive 5-allyl- and 5-allenylcyclopentenethiones 11 and 15. The possible retro-ene reaction eliminating propene or allene from the allylthio or propargylthio moiety has not been observed. Under FVT, the tricyclic thiol 3 led similarly to a mixture of cyclopentadienethiols 19 and 20, the latter tautomerizing to cyclopentenethione 21 upon warming up in solution.
Precursors 7 and 8, corresponding to 2 and 4 in the cyclo-C6 series, behaved quite differently. No thio-Claisen rearrangement occurred, and the allylthio- and propargylthiocyclohex-adienes 22 and 24 evoluted towards stable compounds resulting from competitive retro-ene reactions and β-eliminations. Upon FVT, the cyclobutanic precursor 10 gave quantitatively a mixture of cyclopentadiene, propene and thiophene, presumably via the cyclobutenic intermediate 26.
