A solid-phase synthesis of N,N '-disubstituted ureas and perhydroimidazo[1,5-a]pyrazines via the Curtius rearrangement

[GRAPHICS] An efficient method for trapping isocyanates, generated from the Curtius re arrangement, with resin-bound amines is reported. A commercially available carboxylic acid is treated with diphenylphosphoryl azide, followed by therm al rearrangement, cooling, and trapping in one pot. Cleavage from the resin gives an N,N'-disubstituted urea in excellent purity, as demonstrated with several heterocyclic and aliphatic carboxylic acids. Further utility is sh own by preparing several novel perhydroimidazo[1,5-a]pyrazines.