Fig. 4: Synthesis of the common sarpagine type skeletons.

After construction of the bridged E-ring via SmI2 mediated SET reaction, the double bonds were assembled by Wittig reaction (E-selectivity) and Julia olefination (Z-selectivity). DIPEA diisopropylethylamine, DMF N,N-dimethylformamide, HMPA hexamethylphosphoramide, Me methyl, Ph phenyl, TEA triethylamine, Tf trifluoromethanesulfonyl, TFA trifluoroacetic acid, Et ethyl, NaHMDS sodium bis(trimethylsilyl)amide.