Catalytic transformation of carbon dioxide into seven-membered heterocycles and their domino transformation into bicyclic oxazolidinones

Converting carbon dioxide (CO₂) into valuable heterocycles is of great synthetic value but is usually limited to five- and six-membered ring compounds. Here, we report a catalytic approach for transforming this carbon renewable into seven-membered heterocycles using a double-stage approach, combining a silver-catalyzed alkyne/CO₂ coupling and a subsequent base-catalyzed ring-expansion. This methodology avoids the formation of thermodynamically more stable, smaller-ring by-products and has good functional group tolerance. The synthetic application of these larger-ring cyclic carbonates is further demonstrated by showing their unique ability to serve as synthons for the preparation of bicyclic oxazolidinone pharmacores through an intramolecular domino sequence that involves a transient ketimine group, and various other intermolecular transformations. The results described herein significantly expand on the use of CO₂ as a cheap and versatile carbon feedstock generating elusive heterocycles and pharmaceutically relevant compounds.