A modular and divergent approach for the total synthesis of Elaeocarpus alkaloids

Herein we report a unified strategy for the divergent total synthesis of six Elaeocarpus alkaloids in 6-10 steps from commercially available materials. This modular approach relied on the rapid construction of the tetrahydrobenzopyran-4-one framework through an aldol/dehydration/oxa-Michael process to set all carbons and functional groups ready for the core construction. A key NbCl5-mediated intramolecular Mannich reaction was used to build the C ring and secure both stereoisomers existing in these natural products. Finally, a diversification was achieved through the intermediacy of thioamide, with the side chain of elaeocarfoline A/B installed by an Eschenmoser sulfide contraction/reduction sequence.