Synthesis and reactions of pentafulvenyl-tropones and tropothiones

2-(1′,3′-Di-tert-butyl-pentafulven-6′-yl)-tropone (7) was synthesized by reaction of 6-lithio-1,3-di-tert-butyl-pentafulvene (5) with 2-chlorotropone (6). At elevated temperatures 7 cyclizes to a mixture of the tautomeric azulene derivatives 8 and 9. With P2S5 7 is transformed into the spiroadduct 12, presumably via the pentafulvenyl-tropothione 11, which could not be isolated. Compound 12 reacts by a thermally induced rearrangement to the stable cyclohepta-thialene derivative 14.