A convenient access to iodinated calix[4]arenes1

Benzyltrimethylammonium dichloroiodate (BTMA·ICl2) is recommended as a new iodinating reagent for the phenolic units in calix[4]arenes. Using a mercury salt method for the iodination of calix[4]arenes with free phenolic units the formation of quinones was observed as a side reaction.