Multi-step radical spiro-cyclization of an alkynylaryl isothiocyanate

Cyclohexyl radicals, generated by decomposition of dibenzoyl peroxide in cyclohexane, add to 2-(2-phenylethynyl)phenyl isothiocyanate to afford thioimidoyl radicals. Despite the unfavorable fragmentation equilibrium, these radicals give rise to a multi-step cyclization/H-translocation process yielding a spiranic polycondensed heterocyclic compound. An analogous spiranic dihydro-derivative is obtained by reaction of the corresponding alkynyl isonitrile with cyclohexanethiol under radical conditions.