Ni-Catalyzed Larock Indenone Annulation with Aliphatic- and Silyl-Substituted Alkynes Supported by Mechanistic Analysis

A Ni-catalyzed annulation reaction to synthesize indenones is reported. The reaction provides high yields and regioselectivities when aliphatic- and silyl-substituted alkynes are employed. Both have been challenging and underutilized substrate classes. Several mechanistic observations aided in the development of this reaction, including that β-hydride elimination is turnover-limiting for ortho-halogenated aldehyde substrates and that alkyne dissociation is rate-limiting for internal aliphatic alkynes. We anticipate that these methods will be rapidly adopted due to their synthetic ease and inherent versatility. We also anticipate that the mechanistic conclusions will inform further reaction development.