Insertion of phenyl isocyanide into ethanol catalysed simultaneously by copper(I) and base

Abstract
The insertion of phenyl isocyanide into ethanol under the influence of base and Cu(PhNC)4BF4 is investigated mechanistically. In pre‐equilibria the BF4 anion is exchanged for OC2H5. By intramolecular nucleophilic attack of OC2H5 on coordinated isocyanide an [(ethoxy)‐(phenylimino)methyl]copper intermediate is formed. The substituent effect supports this conclusion. In a rapid reaction with ethanol the intermediate decomposes and the insertion product, ethyl N‐phenylformimidate, is formed. It reacts slowly to give N,N′‐diphenylformamidine, which is precipitated at the end of the reaction as a copper complex.