Simple two step reaction towards a 2,7,14,21-tetraoxocalix[4]arene via bridge brominated intermediate

Bridge perbromination and oxidation of tetramethoxycalix[4]arene 1 with twofold excess of N-bromosuccinimide in wet CHCl3 gives the respective tetraoxo derivative 2 in high yields. A crystal structure of 2 with CHCl3 reveals the chalice in the rare 1,3-alternate conformation with a channel-like architecture of solvent inclusion.