Reagent- and Ligand-Dependent Mechanistic Trichotomy in Fe-Catalyzed Borylative Cyclizations of Enynes.

Based on some very recent results on Fe-catalyzed boron-source-dependent regiodivergent hydroborations of internal alkynes, we report here a boron-source-dependent but also ligand-dependent mechanistic trichotomy in borylative cyclizations. The choice of ligand plus boron source allows the synthesis of three isomeric borylative cyclization products starting from a common substrate and using the same precatalyst ((PhP)Fe(CO)(NO)H) and sets the stage for the development of a unifying concept in Fe-catalyzed borylative cyclizations.