A concise Diels–Alder strategy leading to congeners of the ABC ring system of the marine alkaloid ‘upenamide

[Display omitted] •Stereocontrolled Diels–Alder reaction.•Intramolecular Staudinger reaction.•Quaternary stereocenter.•Marine alkaloid. A second-generation approach to the BC spirocycle of ‘upenamide is reported. Central to the synthesis is an endo selective Diels–Alder reaction between 1-(t-butyldimethylsiloxy)-1,3-butadiene and bromomaleic anhydride followed by a radical mediated allylation of the ring fusion bromide. Functional group manipulation provides three (9–11) advanced synthetic intermediates ready for coupling with the remaining half (DE bicycle) of ‘upenamide.