The intriguing structural complexity and bioactivities of the Daphniphyllum alkaloids have long attracted much attention. Herein, we report the first and enantioselective total synthesis of Daphniphyllum alkaloid dapholdhamine B and its lactone derivative. The chemical structure of dapholdhamine B contains a unique aza-adamantane core skeleton and eight contiguous stereocenters, including three contiguous fully substituted stereocenters, which present a formidable synthetic challenge. This concise approach used to achieve the first synthesis of an aza-adamantane natural product features a vinylogous Mannich reaction, an optimized α-bromo-α,β-unsaturated ketone synthesis, a substrate-dependent intramolecular aza-Michael addition, a key annulation via amide activation, an SN2′-type lactonization, and a facile Horner–Wadsworth–Emmons reaction that converts the hemiacetal moiety to the corresponding homologated carboxylic acid.

The synthetically challenging, diverse chemical skeletons and promising biological profiles of the Daphniphyllum alkaloids have generated intense interest from the synthetic chemistry community. Herein, the first and enantioselective total synthesis of (−)-caldaphnidine O, a complex bukittinggine-type Daphniphyllum alkaloid, is described. The key transformations in this concise approach included an intramolecular aza-Michael addition, a ring expansion reaction sequence, a Sm(II)/ Fe(III)-mediated Kagan−Molander coupling, and the rapid formation of the entire hexacyclic ring skeleton of the target molecule via a radical cyclization cascade reaction, which was inspired by an unexpected radical detosylation observed in our recent dapholdhamine B synthesis.

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A short, enantioselective synthesis of a newly identified ABA receptor agonist (−)-phaseic acid is described.

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