Total synthesis of quebrachamine through macrolactamization

The total synthesis of quebrachamine was achieved through the macrolactamization of cis-2-alkenylated indole 17, which was prepared by a Sonogashira reaction between indole 5b and piperidine 11 followed by cis-hydrogenation. We found that stoichiometric copper(I) iodide limited the undesired Glaser-type homocoupling of alkyne 11 that would otherwise take place during the Sonogashira coupling. This direct approach allowed the total synthesis in ten linear steps starting from commercially available chemicals. Conditions for the reduction of lactam 19 by lithium aluminiumhydride were adjustable, so that either (±)-quebrachamine or the analogue (±)-kopsiyunnanine D was prepared.