A Facile Method for the Synthesis of Polycyclic Indole Derivatives:  The Generation and Reaction of Tungsten-Containing Azomethine Ylides

Treatment of N-(o-alkynylphenyl)imine derivatives with W(CO)(5)(L) induces the 5-endo-mode of cyclization of the imine nitrogen onto the electrophilically activated alkyne moiety to afford a novel reactive species, a metal-containing azomethine ylide. [3 + 2] cycloaddition of this ylide species with various electron-rich alkenes proceeds smoothly to give unstable carbene complexes, which in turn undergo 1,2-hydrogen-, alkyl-, and aryl-migration to afford in good yield 6-5-5 tricyclic indole skeletons having an alkyl or an aryl substituent at the 3-position of the indole nucleus.