Structural requirement for antitumor activity of tropolonederivatives 2-4 was explored. Isochroman derivatives (6-17, 20, and 23) and alpha, alpha-disubstituted compounds 26-30 were synthesized and their antitumor activities were tested. These nontroponoid derivatives were all inactive, implying that a tropolone ring is essential for the activity. Several compounds related to the monotropolone analogue