Pd(II)-Mediated Cyclization of o-Allylbenzaldehydes in Water: A Novel Synthesis of Isocoumarins

A novel, concise and efficient synthesis of substituted isocoumarins is disclosed. o-Allylbenzaldehydes prepared from isovanillin were mediated by PdCl2-CuCl2 in water to undergo a domino reaction sequence, including 6-exo-trig cyclization, the addition of water, the elimination of PdHCl, the isomerization of carbon-carbon double bond, the oxidation of hemiacetals with the elimination of PdHCl, and regeneration of PdCl2 in situ to yield a series of new substituted isocoumarins in high yields, in one pot.