Total Synthesis of the Natural Carbazoles O -Demethylmurrayanine and Murrastanine A, and of a C4,C4′ Symmetric Murrastanine A Dimer from N -Phenyl-4,5-dimethylene-1,3-oxazolidin-2-one

The synthesis of natural carbazoles O -demethylmurrayanine and murrastanine A starting from the title exo -heterocyclic diene- is described. In the synthesis of murrastanine A, its symmetric C4,C4′ dimer can be obtained as the sole product under rather mild conditions. In all cases, the key intermediate is the same diarylamine. The carbazole nucleus is obtained through a Pd-promoted cyclization of the appropriate diarylamine. For the synthesis of O -demethylmurrayanine, the cyclization takes place on a silylated derivative. The crystal structures of murrayanine, two diarylamines, and two non-natural carbazole intermediates are also presented.