A Practical Amine-Free Synthesis of Symmetric Ureas and Thioureas by Self-Condensation of Iso(thio)cyanates - Jiménez Blanco, José L; Saitz Barría, Claudio; Benito, Juan M; Ortiz Mellet, Carmen; Fuentes, José; Santoyo-González, Francisco; García Fernández, José M (Synthesis, 1999)