Stereoselective synthesis of an eleganine A core

A synthetic approach towards the core of a structurally unique cytotoxic indole alkaloid eleganine A has been accomplished for the first time. The synthesis features a stereoselective Ireland–Claisen rearrangement as the key step, enabling the installation of 2 stereogenic centers and a stereodefined double bond in a single step. Furthermore, a SnCl₄ promoted acylation of the indole C-2 position allows the coupling of a highly functionalized 4-ethylidene proline fragment with the indole part.