[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.