Transition metal-catalysed asymmetric umpolung reactions of electron-deficient π-unsaturated systems

The umpolung reaction of electrophilic π-unsaturated compounds represents a powerful strategy to reverse inherent polarity, enabling unconventional bond formations. While organic σ-Lewis base catalysts are classically utilised, in this feature article, recent advances in the low valent transition metal-mediated asymmetric umpolung reactions of diverse electron-poor unsaturated systems, usually in a diene form, are reviewed, proceeding through either an oxidative cyclometallation or a π-Lewis base activation mechanism. The contents are organised according to transition metal categories, with emphasis on catalytic mechanisms, regio- and stereoselectivity control, and limitations.