N−H Insertion Reactions of Primary Ureas:  The Synthesis of Highly Substituted Imidazolones and Imidazoles from Diazocarbonyls

Primary ureas have been used as substrates in rhodium-catalyzed N−H insertion reactions with an array of diazocarbonyls. The insertion reaction is efficient and gives excellent selectivity and yields. The products from the insertion reaction with diazoketones cyclize readily in the presence of acid to yield the corresponding imidazolones that can be further derivatized by N-alkylation with alkyl, allyl, and benzyl halides. Alternatively, the imidazolones were treated with phosphorus oxybromide to form the corresponding 2-bromoimidazoles that were further functionalized using a Suzuki coupling reaction.