Recovering phospholes from phosphacymantrenes

Several attempts to recover phospholes from phosphacymantrenes are described. UV irradiation gives 1,1′-biphospholes when the ring carries two phenyl substituents. Lithium reduction appears to give somewhat erratic results. Exo-attack by phenyllithium leads to η4-anionic complexes derived from the corresponding 1-phenylphospholes. Quite surprisingly, this attack by phenyllithium is compatible with a carbonyl fonctionality on the ring. These anionic complexes yield η4-phospholium derivatives upon quaternization of phosphorus with BrCH2CH2Z (Z=CN, COOEt). One of these phospholium complexes has been caracterized by X-ray crystal structure analysis.