Selenophene

Selenophene is an unsaturated organic compound containing a five member ring with selenium with formula C4H4Se. It is a metallole with reduced aromatic character compared to thiophene.
Nomenclature.
Atoms in selenophene are numbered sequentially around the ring, starting with the selenium atom as number 1 following normal systematic nomenclature rules. Oxidized forms include selenophene 1,1-dioxide. Related ring structures include those with only one double bond (2-selenolene and 3-selenolene) and the fully saturated structure selenolane.
Production.
Although Ida Foa claimed to have made selenophene in 1909, the first confirmed production was by Mazza and Solazzo in 1927. They heated acetylene and selenium together at about 300 °C. The selenium burst into flame, and up to 15% selenophene was formed, along with selenonaphthene. Another way to make it is from furan heated with hydrogen selenide and aluminium at 400 °C.
Substituted selenophenes can be made using a Fiesselman procedure in which a β-chloro-aldehyde reacts with sodium selenide, and then ethyl bromoacetate.
Properties.
The selenophene molecule is flat and aromatic. Being aromatic, it undergoes electrophilic substitution reactions at the 2- or 2,5-positions. These reactions are slower than that of furan, but faster than thiophene.