Transition metal-catalyzed Allene hydroaminations represent an attractive approach to N-heterocycle formation. While formation of five and six-membered heterocycles is common under Rh catalysis, reports on the formation of medium and large-sized heterocycles are rare. Here we report that a bimetallic Rh(I) catalyst based on a 2-phosphinoimidazole ligand enables efficient medium-size ring formation via an allene hydroamination mechanism. We demonstrate that a variety of 8–10-membered heterocycles are easily formed with our bimetallic catalyst in high yield. Our mechanistic studies confirm that the bimetallic nature of the catalyst is essential for reactivity, as monometallic Rh complexes fail to give any cyclization for medium-sized heterocycle formation.

Formation of medium and large N-heterocycles via bimetallic Rh(I)–Rh(I) catalyzed allene hydroamination

ACS Spring 2022

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