A Simple and Efficient Synthesis of Diaryl Ureas with Reduction of the Intermediate Isocyanate by Triethylamine

Thirty symmetrical diaryl urea derivatives were synthesised in moderate to excellent yields from arylamine and triphosgene with triethylamine as a reducing agent for the intermediate, isocyanate. It was significant that part of the products could be collected in almost quantitative yield without column chromatography. The procedure under mild reaction conditions was tolerant of a wide range of functional groups. The structures of the compounds were determined by NMR, MS and X-ray crystallographic analyses.