A new antifungal compound, (3S)-4,6-dihydro-8-methoxy-3,5-dimethyl-6-oxo-3H-2-benzopyran (4), was isolated from Penicillium expansum. During the isolation procedure 4 was determined to be unstable and readily reacted with methanol, ethanol, and water, forming three new isochromans, (1S,3S)-6-hydroxy-1,8-dimethoxy-3,5-dimethylisochroman (1), 1-ethoxy-6-hydroxy-8-methoxy-3,5-dimethylisochroman (2), and 1,6-dihydroxy-8-methoxy-3,5-dimethylisochroman (3), respectively. (3S)-6-Hydroxy-8-methoxy-3,5-dimethylisochroman (5) was reisolated from P. expansum. In fungicide disk assays, compounds 1, 2, and 4 inhibited the mycelial growth of Lasiodiplodia theobromae at 100 microg/mL by 76%, 74%, and 69%, respectively.