Palladium-Catalyzed Cross-Coupling of Aryl Chlorides and Triflates with Sodium Cyanate: A Practical Synthesis of Unsymmetrical Ureas

An efficient method for palladium-catalyzed cross-coupling
of aryl
chlorides and triflates with sodium cyanate is reported. The protocol
allows for the synthesis of unsymmetrical N,N′-di- and N,N,N′-trisubstituted
ureas in one pot and is tolerant of a wide range of functional groups.
Insight into the mechanism of aryl isocyanate formation was gleaned
through studies of the transmetalation and reductive elimination steps
of the reaction, including the first demonstration of reductive elimination
from an arylpalladium isocyanate complex to produce an aryl isocyanate.