Trimethyl Phosphite Mediated Simple Synthesis of Coumarins and Azacoumarins Through the Reaction of Phenols or Hydroxypyridines and Dimethyl Acetylenedicarboxylate (DMAD) or Diethyl Acetylenedicarboxylate (DEAD)

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Protonation of the reactive intermediate produced in the  reaction between trimethyl phosphite and dimethyl acetylenedicarboxylate or diethyl acetylenedicarboxylate by resorcinol, 5-methylresorcinol, 2,5-dihydroxyacetophenone, 4-chloro-2-methylphenol, 4-chloro-3,5-dimethy-lphenol, 4-hydroxypyridine, 2-hydroxypyridine, 3-hydroxypyridine, or 8-hydroxyquinoline leads to vinylphosphonium salts, which undergo Michael addition with the conjugate base of the OH-acid to produce highly functionalized 2-oxo-2H-chromene or azacoumarins in good yields.