Reactions Of Phosphole And Imine

The synthesis of α-C2-bridged biphospholes is obviously interesting because it can offer an access to chelating biphosphines with two chiral phosphorus centers.Unfortunately, until now, only one such biphosphole has been described and its lengthy multistep synthesis precludes its use for further developments. Phospholes react with aldimines at 170 °C in the presence of mild Lewis acids to give C2-bridged biphospholes in good yields. The intermediates of this reaction and DFT computations show that the mechanism includes a [1,5] sigmatropic shift from P to Cα of the sp3 carbon substituent, a condensation of P-H and aldimine, and the formation of a transient three-membered ring. It must be noted that sp3 carbon substituents were thought unble to migrate before.