Rhodium Carbenoid N−H Insertion Reactions of Primary Ureas:  Solution and Solid-Phase Synthesis of Imidazolones

The solution and solid-phase synthesis of imidazolones is reported. The key step for the preparation of these compounds is the N−H insertion reaction of primary ureas into highly reactive rhodium carbenoid intermediates. Typically, a soluble or support-bound α-diazo-β-ketoester is treated with a rhodium carboxylate catalyst in the presence of a primary urea to give the corresponding N−H insertion product. Subsequent acid-catalyzed cyclodehydration of these insertion products affords the desired imidazolone products.