Rice blast fungus, Magnaporthe grisea, produces a series of salicylaldehyde-type phytotoxins such as pyriculol, pyricuol, and pyriculariol. Plausible biosynthetic intermediates of these phytotoxins were synthesized in deuterium labeled forms using the Stille coupling reaction as the key step, and subjected to biotransformation by the fungus. Heptatrienyl-salicylaldehyde was converted into dihydropyriculol by the fungus by a shaking culture. A new biosynthetic pathway comprising both oxidation and reduction is proposed.