Vinyltriphenylphosphonium salt mediated synthesis of functionalized coumarins

Protonation of the reactive 1:1 intermediate produced in the reaction between triphenylphosphine and dimethyl acetylenedicarboxylate by hydroquinone, resorcinol, catechol or pyrogallol leads to vinylphosphonium salts, which undergo Michael addition with the conjugate base of the hydroxy acid to produce highly functionalized 2-oxo-2H-chromene derivatives in good yields.