SYNTHETIC APPLICATIONS OF 2-(1,3-DITHIAN-2-YL)INDOLES .7. SYNTHESIS OF ASPIDOSPERMIDINE

A new method of synthesizing the alkaloid aspidospermidine (1), based on building ring E on the pyridocarbazole [ABCD] ring structure, is re ported. The preparation of the pyridocarbazole framework of Aspidosper ma alkaloids is a new three-step synthetic application of 2-(1,3-dithi an-2-yl)indoles. A tandem conjugate addition-alkylation reaction start ing from indolyldithiane (4), 3-methylenelactam 8, and EtI yields the adduct 17. Treatment of lactam 17 with DIBALH leads to formation of th e naphthyridoindole 18. Compound 18 isomerizes in aqueous AcOH to yiel d pyridocarbazole 3. Finally, closure of ring E and subsequent reducti on of the dithiane ring produces aspidospermidine. Pyridocarbazoles 2 and 10 were prepared as models.