A Versatile Carbonylative Approach to Ureas and Carbamates through Light Activated Nickel Catalyzed Formation of Aliphatic Isocyanates

We describe the development of a nickel-catalyzed route to prepare aliphatic isocyanates via carbonylation chemistry. Unlike thermal reactions, where the affinity of Ni(0) for carbon monoxide has traditionally limited its use in carbonylations, mechanistic studies suggest that visible light excitation of a Xantphos-bound nickel catalyst can enable a radical pathway for the carbonylation of alkyl halides, while the CO-bound nickel drives the formation of a reactive acyl azide product for rapid Curtius rearrangement. Coupling this transformation with subsequent nucleophilic reactions has opened a unique and modular pathway to apply carbonylations to the synthesis of an array of diversely substituted, unsymmetrical ureas and carbamates, including those of relevance to drug design.