Total synthesis of the topopyrones: A new class of topoisomerase I poisons

[GRAPHICS] The topopyrones represent a new class of highly cytotoxic topoisomerase I poisons. Efficient total syntheses of all four naturally occurring members of this class have been accomplished. Key elements of the syntheses include Diels-Alder reactions employing two novel dienes and a titanium-mediated ortho-directed Friedel-Crafts acylation. Additionally, the syntheses of two chlorinated analogues accessible from an advanced intermediate are described.