Enantioselective Synthesis of the Side-Chain Acid of Homoharringtonine and Harringtonine from the Same Γ-Butyrolactone Intermediate

A versatile intermediate gamma-butyrolactone 7 was prepared from L-alanine with 96% ee value, which could be used as a common intermediate for the preparation of the side-chain acid of homoharringtonine and harringtonine in 26.6% and 27% overall yield respectively. The key steps involved [2, 3]-Meisenheimer rearrangement, allylic bromination, and Barbier reaction. Some interesting experimental phenomena and effective solutions to these issues are reported herein.