Calix[4]quinone. Part 1: Synthesis of 5-hydroxycalix[4]arene by calix[4]quinone monoketal route

The oxidation of calix[4]arene tribenzoate 1 with chlorine dioxide yielded the corresponding calix[4]monoquinone tribenzoate 2. Reaction of monoquinone 2 with ethylene glycol under acidic conditions produced the protected monoketal derivative 3. The basic hydrolysis of the benzoate, followed by an acidic cleavage of ketal moieties and a metal hydride reduction of the quinones or vice versa, converted 3 to the title compound, 5-hydroxycalix[4]arene (7).