Transient 2H-Phospholes as Powerful Synthetic Intermediates in Organophosphorus Chemistry

Transient 2H-phospholes are easily obtained from 1-R-1H-phospholes by a [1,5]-shift of the R-substituent from phosphorus to the α-carbons of the ring. They display cyclopentadiene-like chemistry: [4+2]-cycloaddition reactions with alkenes, alkynes, conjugated dienes and aldehydes, deprotonation to give the aromatic phospholide ions, and reaction with transition metal derivatives to give η5-phospholyl complexes. The resulting products have found some use in homogeneous and asymmetric catalysis and show some promise in the field of electroconducting polymers.