Cascade Radical Reactions of Isonitriles: A Second‐Generation Synthesis of (20S)‐Camptothecin, Topotecan, Irinotecan, and GI‐147211C

Complex molecules can be made in short order, as shown in a concise synthesis of the antitumor agent (20S)-camptothecin (1 with R1 = R2 = H), which relies on a cascade radical reaction [Eq. (a)]. This approach also provides a straightforward route to substituted analogs (R1 = H, Et; R2 = OMe, OH), which are immediate precursors of compounds that have better properties for pharmaceutical applications and are currently in clinical trials.