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.