| Abstract
| - Upon treatment with 30 mol % of Co2(CO)8 and 30 mol % of TMTU in toluene at 70 °C, benzene-bridged alkynecarbodiimides efficiently underwent a ring-closing reaction to give the pyrrolo[2,3-b]indol-2-ones in good yields. These conditions could nearly suppress the formation of the urea derivatives,which were consistently observed when 10 mol % of Co2(CO)8 and 60 mol % of TMTU in benzenewere used. The synthesis of the eight hexahydropyrrolo[2,3-b]indole alkaloids was accomplished fromthe resulting pyrrolo[2,3-b]indol-2-ones via the introduction of an angular substituent at the C3a-positionby treatment with NaBH4/alkyl bromide as the crucial step.
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