Total Synthesis of Isodihydrokoumine, (19 Z)-Taberpsychine, and (4 R)-Isodihydroukoumine N4-Oxide.

We report the total synthesis of the natural products isodihydrokoumine and (19 Z)-taberpsychine in 11 steps each and (4 R)-isodihydrokoumine N4-oxide in 12 steps from commercially available starting materials. The key reactions include an intramolecular [3 + 2] nitrone cycloaddition and Lewis acid mediated cyclizations of a common intermediate to provide the core structures of either taberpsychine or isodihydrokoumine.