Reactivity of triplet diphenylcarbene towards the sulphur atom of 1,2,3-benzothiadiazole

Abstract

Thermal decomposition of diphenyldiazomethane (1) at 87 °C in chlorobenzene in the presence of 1,2,3-benzothiadiazole (2) afforded 9-phenylthioxanthen (3), 6-phenyl-6H-dibenzo[b,d]thiopyran (4), 6-benzhydryl-6-phenyl-6H-dibenzo[b,d]thiopyran (5) and thianthren (6). Reaction products are explained in terms of attack on the sulphur atom of (2) by triplet diphenylcarbene, leading to decomposition of the heterocyclic nucleus with loss of nitrogen and formation of a diradical intermediate (7), from which products (3)–(6) can arise. Some evidence is presented that benzothidiazole (2) may act as an an effective spin-trap for triplet diphenylcarbene, thus preventing reversible interconversion of singlet and triplet states.