Total Syntheses of Pleiocarpamine, Normavacurine, and C-Mavacurine.

The total syntheses of C-mavacurine-type indole alkaloids, (±)-pleiocarpamine, (±)-normavacurine, and (±)- C-mavacurine, were accomplished. The key step in the syntheses was the cyclization between the metal carbenoid at C16 and the N1 position in a Corynanthe-type compound that was equipped with a diazo function. For this cyclization, the N4 modification of the substrate using an amine-borane complex was indispensable to fix the molecular conformation.