Selenium-Containing Tetrachalcogenins and Pentachalcogenepins Fused to Aromatic Systems

Various ring‐sized cyclic polychalcogenides fused to aromatic systems were synthesized, and the structures were sufficiently characterized. Stabilities of the rings were examined in terms of the existence of selenium atoms. Benzopolychalcogenides are unstable molecules. However, benzo[1,2,3,4,5]tetrathiaselenepins with an isopropyl group or two methoxy groups on the ring were found to be stable. Similarly, the novel benzo[2,3,4,1,5]trithiadiselenepin ring was also stabilized by two methoxy groups. Benzo[1,2,3,4]trithiaselenin and benzo[2,3,1,4]dithiadiselenin were also synthesized by a controlled reaction with S2Cl2 at –78 °C. The ring systems were sensitive to air, moisture, light, and polar solvents. Extended π‐systems such as naphthalene and phenanthrene showed remarkable thermodynamic stability toward unstable rings. The unprecedented stabilities possessed by the polyaromatics are yet unclear. Phenanthro[9,10‐d][1,2,3]dithiaselenole was also successfully isolated as a novel molecule. It is the first isolated trichalcogenole having one selenium atom, which is stabilized by an extended π system. Phenanthro[9,10‐f][1,2,3,4,5]tetrathiaselenepin is stable in the solid state. The use of polar solvents under ambient conditions resulted in the extrusion of selenium from the ring to generate more stable trithiole rings. The structures of the five‐, six‐, and seven‐membered cyclic polychalcogenides were extensively established in this report.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)