Formal Synthesis of (−)-Cephalotaxine.

A formal synthesis of (−)-cephalotaxine ( 1) by means of a highly stereoselective radical carboazidation process is reported. The synthesis begins with the protected ( S)-cyclopent-2-en-1-ol derivative 10 and uses the concept of self-reproduction of a stereogenic center ( Schemes 5 and 6). For this purpose, the double bond adjacent to the initial chiral center in 10 is converted into an acetonide after stereoselective dihydroxylation. The initial alcohol function is used to build an exocyclic methylene group suitable for the carboazidation process 8→ 7 (Scheme 7). Finally the protected diol moiety is converted back to an alkene ( 14→ 15→ 6) and used for the formation of ring B via a Heck reaction ( 6→(−)- 16; Scheme 8). [ABSTRACT FROM AUTHOR]