Bimetallic Aluminum(salen) Catalyzed Synthesis of Oxazolidinones from Epoxides and Isocyanates

The bimetallic aluminum­(salen) complex [Al­(salen)]2O is shown to catalyze the synthesis of oxazolidinones from epoxides and isocyanates. The reaction is demonstrated to proceed with overall retention of epoxide stereochemistry, and both aromatic and aliphatic isocyanates can be used as substrates. In contrast to the corresponding reactions between epoxides and carbon dioxide or carbon disulfide which are also catalyzed by [Al­(salen)]2O, no cocatalyst is needed in the reactions with isocyanates. A mechanism is proposed which involves breaking and reforming of the Al–O–Al unit during the catalytic cycle, and this is supported by results obtained using monometallic catalysts.