Total synthesis of (±)-martinelline

The squaric acid-catalyzed imino-Diels–Alder reaction of enamine 4 with the imine 5 provides the pyrroloquinolines 6 and 7, which were converted to the triamine 3 using regioselective reduction and a Wittig reaction as the key steps. Guanylation of 3 followed by coupling with the alcohol 19 furnished the total synthesis of (±)-martinelline.