Synthesis of the tricyclic core of manzamine AElectronic supplementary information (ESI) available. CCDC 1025236. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4ob02582b

An efficient synthetic approach to the core structure of the manzamine alkaloids is reported, particularly in relation to incorporating a one-carbon unit in ring B from which the aldehyde in ircinal A or the beta-carboline unit in manzamine A could potentially be generated. The key steps involve a Johnson-Claisen rearrangement, enolate alkylation, dithiane alkylation and a stereoselective intramolecular dipolar cycloaddition of an azomethine ylide, which provided the desired tricyclic ABC core structure. An approach to the ABC tricyclic ring system of the manzamine alkaloids has been achieved. A key step is the intramolecular dipolar cycloaddition of an azomethine ylide.