Phosphole

Phosphole is an organic compound with the chemical formula C4H5P; it is the phosphorus analog of pyrrole.The first phosphole was discovered in 1953, hexaphenylphosphole followed in 1959 and the parent compound, phosphole itself, was first synthesized in 1987.

Unlike other the 5-membered heterocycles pyrrole, thiophene and furan this compound is not considered an aromatic compound because unlike nitrogen, phosphorus is reluctant to share its lone pair in delocalization.