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

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.