Gold as Catalyst for the Hydroarylation and Domino Hydroarylation/N1-C4 Cleavage of β-Lactam-Tethered Allenyl Indoles.

Gold-catalyzed hydroarylation reaction of β-lactam-tethered allenyl indoles gives azeto-oxepino[4,5-b]indol-2-ones, tetrahydroazeto-azocino[3,4-b]indol-2-ones, and hexahydroazeto-azepino[3,4-b]indol-2-ones with very high levels of stereo- and regioselectivity, the 7-exo and 8-endo carbocyclization modes by attack of the indole group toward either the internal or the terminal allene carbon, respectively, being favored. Hydroarylation across the central carbon of the allene moiety has not been detected. The controlled gold-catalyzed annulations allowed the formation of fused β-lactams without harming the sensitive four-membered heterocycle. Besides, a novel gold-catalyzed domino process, namely, the allenic hydroarylation/N1-C4 β-lactam bond breakage to afford dihydro-oxepino[4,5-b]indole-4-carboxamides, has been discovered.