Ruthenium Complex-Catalyzed Domino Addition/exo-Cycloisomerization of Propargylic Alcohols and Tosyl Isocyanate to Form Oxazolidinones

A ruthenium complex with a tetradentate nitrogen-phosphorus mixed ligand is shown to be an efficient catalyst for domino addition/exo-cycloisomerization of propargylic alcohols and tosyl isocyanate. In the presence of 2-5 mol% ruthenium complex, a range of terminal propargylic alcohols were reacted with tosyl isocyanate to furnish the corresponding oxazolidinone product exclusively in moderate to excellent yields. Mechanistic studies suggest that propargylic alcohol and tosyl isocyanate undergo addition firstly to generate propargylic carbamate, which is then activated by the ruthenium complex to form an eta(2)-alkyne complex, rather than the ruthenium vinylidene intermediate, to afford the final oxazolidinone product.