Concise Total Synthesis of Tronocarpine

Abstract

A concise total synthesis of tronocarpine, a chippiine-type indole alkaloid, was accomplished. The key feature of this total synthesis is a one-pot construction of the pentacyclic skeleton containing an azabicyclo[3.3.1]nonane core by tandem cyclization from an indole derivative with all carbon side chains and functional groups. This tandem cyclization consists of α,β-unsaturated aldehyde formation, intramolecular aldol reaction, six-membered lactamization, azide reduction, and seven-membered lactamization. The stereochemical outcome in this tandem cyclization is controlled by the stereocenter at the C14 position. This strategy can be utilized to synthesize other chippiine-type alkaloids with azabicyclo[3.3.1]nonane skeletons.

Keywords: alkaloids; equilibrium; natural products; tandem cyclization; total synthesis.