Thiophene-Fused π‑Systems from Diarylacetylenes and Elemental Sulfur

A simple
yet effective method for the formation of thiophene-fused
π-systems is reported. When arylethynyl-substituted polycyclic
arenes were heated in DMF in the presence of elemental sulfur, the
corresponding thiophene-fused polycyclic arenes were obtained via
cleavage of the ortho-C–H bond. Thus, arylethynylated
naphthalenes, fluoranthenes, pyrenes, corannulenes, chrysenes, and
benzo­[c]­naphtho­[2,1-p]­chrysenes were effectively converted into the corresponding
thiophene-fused π-systems. Apart from polycyclic hydrocarbons,
thiophene derivatives are also susceptible to this reaction. The practical
utility of this reaction is demonstrated by preparations on the decagram
scale, one-pot two-step reaction sequences, and multiple thiophene
annulations.