A New Route to 4-Ethynyl-N-hydroxy-2-imidazolidinones via Oxime Addition

A rapid route was developed to afford ethynyl-substituted imidazole derivatives which served as key compounds for aryl–alkynyl-coupling reactions. Addition of mono-silylated acetylene to O-protected oximes was carried out in the absence of Lewis acids, directly affording the title compounds 3a–c in a one-pot reaction. Limitations and dependence of the feasibility on N1-substituents are discussed.