Metal-Mediated Heterocyclic Annulation to Indolopyrrolidines

Significance

An elegant two-step in situ transformation of ortho-acetylenic arylimines to annulated indoles under transition-metal and gold catalysis is reported. Comprehensive catalyst screening indicates that simple Pt(II) and Au(III) halides serve as the most active catalysts for this reaction due to their moderate Lewis acidity. Mechanistically, the transformation is believed to proceed via a metallo-azomethine ylide which undergoes [3+2] cycloaddition to form a tricyclic metalocarbene and eventually, after 1,2-R group migration and metal elimination, leads to the tricyclic indole derivative in high yields but low stereoselectivities.