Asymmetric total synthesis of (20R)-homocamptothecin, substituted homocamptothecins and homosilatecans

An efficient asymmetric synthesis of a key DE lactone pyridone intermediate in the synthesis of homocamptothecin is reported. The synthesis is scalable and features a Stille coupling and a Sharpless asymmetric epoxidation as the key steps. The key intermediate has been parleyed into homocamptothecin and an assortment of fluorinated homocamptothecins and homosilatecans (7-silylhomocamptothecins), thereby providing the first asymmetric entry to this important new class of antitumor agents.