Catalyst- and solvent-free regiospecific SNHAr phosphinylation of pyridines with H-phosphinates mediated by benzoylphenylacetylene†

Pyridines undergo a facile S_N^HAr phosphinylation with H-phosphinates under catalyst- and solvent-free conditions (50–55 °C) in the presence of benzoylphenylacetylene to afford 4-phosphinylpyridines in up to 68% yield. In this reaction, benzoylphenylacetylene activates the pyridine ring by the formation of a 1,3(4)-dipolar complex, deprotonates H-phosphinates to generate P-centered anions and finally acts as an oxidizer, being eliminated from an intermediate ion pair. Terminal electron-deficient acetylenes (methyl propiolate and benzoylacetylene) are inefficient as mediators in the above S_N^HAr process.