Redox Switching in Ethenyl‐Bridged Bisphospholes

A 2e − /2H + redox platform has been implemented in the ethenyl‐bridged bisphosphol‐3‐ol 1 to afford the first phospholes that feature chemically reversible oxidations. Oxidation of the title compounds to the corresponding bisphosphol‐3‐one 2 leads to a change in conjugation topology and a concomitant hypsochromic shift of the lowest‐energy absorption maximum by 100 nm. Electrochemical oxidation proceeds without any detectable intermediates, whereas the deprotonated form of 1 can be observed in an aprotic medium during the reduction of 2 . This dianionic intermediate 3 is characterized by end absorptions that are bathochromically shifted by circa 200 nm compared to those of 2 .