The 2-Vinylphosphirane−3-Phospholene Rearrangement: Biradicaloid and Concerted Features

Abstract

Activation parameters have been determined for the 2-vinylphosphirane−3-phospholene rearrangement in the cycloheptane annellated series 7 → 8. For the thermal reaction, the mean activation parameters (ΔH⧧ = 125 ± 5 kJ mol-1 and ΔS⧧ = −1 ± 14 J K-1 mol-1) are as expected for a biradicaloid character of the transition structure. In the presence of Cu(I) as a catalyst, the activation parameters for this conversion (ΔH⧧ = 80.2 ± 3 kJ mol-1 and ΔS⧧ = −100 ± 7 J K-1 mol-1) are strikingly different and more in line with a concerted pathway.