Complete bromination of calix[4]arene by improved direct synthesis

Since the pioneering work of Gutsche on calix[n]arenes, many functionalized calixarenes have been prepared. The full bromination of calix[4]arene by a direct process has been regarded as unavailable. Therefore, a more circuitous route including three steps has been developed. But in the present work p-tetrabromocalix[4]arene, which serves as a potential intermediate to derive functionalized calixarenes, is successfully synthesized with a high yield by an improved direct bromination procedure. The analytical results are in complete accordance with those reported in previous literature. The reason why the conventional methods cannot provide full bromination is discussed.