Cyclohepta<b>-indoles are tricyclic compounds with a seven-membered ring fused with an indole. They are present in many bioactive natural products and pharmaceuticals. We recently developed an efficient and versatile tandem indole annulation and [4+3] cycloaddition process for the synthesis of cyclohept<b> indoles. This method allows simultaneous construction of both the indole and the seven-membered ring. Various substituted cyclohepta<b>indoles were prepared from readily available propargylic ethers and dienes. Both acyclic and cyclic dienes including furans participated in the [4+3] cycloaddition to afford tri- and tetracyclic products, respectively. For some substituted furans, small amount of arylation products were also obtained. When N-methylpyrrole was employed, only arylation product was observed. We proposed that Pt(II) or Rh(I) carbene intermediates were involved in this tandem process.  Electron-deficient phosphine or phosphite ligands often facilitated the formation of these carbene intermediates.

Rhodium- and platinum-catalyzed tandem indole annulation and [4+3] cycloaddition

247th National Meeting (2014)

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