Resonance des Phospholes—Reaction Avec le n-Butyl Lithium

Seven phospholes were prepared by a two-step synthesis as previously described. On the basis of H and ³¹P NMR data, these phospholes were tentatively classified by their degree of aromaticity. Two of these were reacted with n-butyl lithium. Nucleophilic attacks were observed on the phosphorus atom and on the double bonds. These facts are explained by enhanced p—π and p_π—d_π conjugations between the phosphorus atom and the dienic system by comparison with vinyl phosphines. NMR data seem to support this view. The influence on δ ³¹P of substitution and cyclic delocalization of the lone pair of electrons on phosphorus is interpreted within the Letcher-Van Wazer formalism.