Metal-free SHN cross-coupling of pyridines with phosphine chalcogenides: polarization/deprotonation/oxidation effects of electron-deficient acetylenes

Terminal acylacetylenes, typical electron-deficient acetylenes, drive SHN cross-coupling of pyridines with secondary phosphine chalcogenides under metal-free mild conditions (20-75 1C) to afford 4chalcogenophosphorylpyridines in up to 70% yield. The reaction proceeds via 2,4-migration of chalcogenophosphoryl groups in the intermediate 1-acylvinyl-2-phosphoryl dihydropyridines with simultaneous redox elimination of the vinyl ketone oligomers. These results are generalized in a concept of trimodal (polarization/deprotonation/oxidation) catalyst-like assistance of electron-deficient acetylenes in SHN reaction of the pyridinoid heterocycles with PH-nucleophiles, which comprises: (i) repolarization (umpolung) of the pyridine ring, (ii) deprotonation of secondary phosphine chalcogenides to generate phosphorus-centered anions and (iii) oxidation of the dihydro intermediates.

Automated summary

This study demonstrates that terminal acylacetylenes can catalyze the reaction of pyridines with secondary phosphine chalcogenides to produce chalcogenophosphorylpyridines under metal-free mild conditions. The mechanism involves migration of chalcogenophosphoryl groups in the intermediate and simultaneous redox elimination of vinyl ketone oligomers.