Divergent Construction of N-Doped Polycyclic Aromatic Hydrocarbons with Indole as the Nitrogen Source Building Block

An Ag/Au-catalyzed divergent cascade reaction of alkyne embedded diazoketones with indoles has been described. Preliminary mechanistic studies indicate that the reaction goes through a [4+2]-cycloaddition of an in situ formed isobenzopyrylium intermediate with indole, followed by a sequential retro-Michael addition/carbene N-H insertion process to give the benzophenanthridines products with gold catalysis; whereas a dearomatization/rearomatization sequence occurs favourably when the reaction is catalyzed by a silver catalyst, delivering benzo[b]carbazoles in generally high to excellent yields. Notably, this is a rare example of using indole as the dienophile for cycloaddition with the isobenzopyrylium species, providing a concise and practical approach for the selective construction of N-doped polycyclic aromatic hydrocarbons (PAHs) with structural diversity and broad functional-group compatibility.

Automated summary

In this study, an Ag/Au-catalyzed cascade reaction of alkyne embedded diazoketones with indoles has been reported. Mechanistic studies indicate that the reaction involves a [4+2] cycloaddition followed by a retro-Michael addition/carbene N-H insertion process with gold catalysis, and a dearomatization/rearomatization sequence with silver catalysis, leading to the selective construction of N-doped polycyclic aromatic hydrocarbons (PAHs) with diverse structures and functional groups.