Diastereoselective synthesis of quinolizidin-4-one and indolizidin-3-one derivatives with a spirocyclic motif via cascade cyclization using a gold(I)/Brønsted acid relay catalysis

Functionalized quinolizidin-4-ones and indolizidin-3-ones were synthesized from mixed N,O-acetals with a terminal alkyne unit and nucleophiles with two reactive sites by a gold(I)/Bronsted acid relay catalysis with 40–90% yield. The reactions are proposed to proceed through gold-catalyzed carboalkoxylation of the alkynes with the internal mixed N,O-acetals, giving the corresponding cyclic enols, which are transformed to spirocyclic compounds by a Bronsted acid catalyst. The latter spirocyclization process occurs under thermodynamic control, providing polycyclic quinolizidin-4-one and indolizidin-3-one derivatives diastereoselectively.