Synthesis of N‑Styrenyl Amidines from α,β-Unsaturated Nitrones and Isocyanates through CO2 Elimination and Styrenyl Migration

A mild, metal-free, and modular route for the preparation of N-styrenyl amidines from N-aryl-α,β-unsaturated nitrones and isocyanates has been developed that accesses an initial oxadiazolidinone intermediate that can undergo CO2 elimination and styrenyl migration. The use of a migration event to install N-styrenyl amidine substituents circumvents a limitation of traditional Pinner-type methods for amidine synthesis that require the use of amine nucleophiles. The modularity of the nitrone and isocyanate reagents provides access to a variety of differentially substituted N-styrenyl amidines. The scope and tolerance of the method are presented, and preliminary mechanistic data for the transformation are discussed.