The pyrolysis products of tetrahydrodesoxyusnic acid were proved to be 7-acetyl-3, 5-dimethyl-6-hydroxycoumaran-2-one (I), 7-acetyl-3-ethyl-5-methyl-6-hydroxycoumaran-2-one (III), methyl ethyl ketone and methyl n-propyl ketone. The reaction mechanism of the pyrolysis of tetrahydrodesoxyusnic- and dihydrousnic-acids was discussed.
