Rhodium‐ and Platinum‐Catalyzed [4+3] Cycloaddition with Concomitant Indole Annulation: Synthesis of Cyclohepta[b]indoles

Various substituted cyclohepta[b]indoles were prepared from propargylic ethers and dienes by a tandem indole annulation/[4+3] cycloaddition (see scheme; Boc=tert-butoxycarbonyl). Both acyclic and cyclic dienes participated in the [4+3] cycloaddition to afford tri- and tetracyclic products, respectively. Electron-deficient phosphine or phosphite ligands facilitated the tandem reaction.