Synthesis of new sulfur heteroaromatics isoelectronic with dibenzo[g,p]chrysene by photocyclization of thienyl- and phenyl-substituted ethenes

A series of new sulfur heteroarenes, isoelectronic with dibenzo[g,p]chrysene, have been prepared by double photocyclization of the corresponding tetraaryl substituted ethenes. The first step proceeds efficiently in each case, and the corresponding intermediate sulfur heteroarenes, isoelectronic with phenanthrene, have been isolated. The second ring closure is only efficient when one of the participating aryl substituents is thienyl, which thus manifests a higher electron density on the carbon atom involved in the excited singlet state reaction. Most of the new compounds are of minimal solubility in common solvents and do not display improved electron donor properties otherwise commonly found among heteroaromatics.