[5 + 2] Cycloaddition Reaction of 2-Vinylaziridines and Sulfonyl Isocyanates. Synthesis of Seven-Membered Cyclic Ureas

The [5 + 2] cycloaddition reaction of 2-vinylaziridines with sulfonyl isocyanates proceeded smoothly under mild conditions, and various cyclic ureas were isolated in high yields. The remarkable solvent effect on the reaction was observed, and the preferential formation of the seven-membered ring occurred when the reaction was carried out in CH2Cl2. The scope and limitation were studied, and the mechanism of this reaction was discussed. This study provides a new and simple method for the synthesis of seven-membered cyclic ureas.