Regioselective Halogenation of Thiacalix[4]arenes in the Cone and 1,3-Alternate Conformations

Monohalogenation of thiacalix[4]­arene in the cone conformation gave either the meta- or para-substituted isomers depending on the halogen and reaction conditions used. Surprisingly, the same reaction with the 1,3-alternate conformer led only to the meta isomer. This is the first example of such a conformation-dependent regioselectivity in calixarene/thiacalixarene chemistry. As the halogen-substituted calixarenes are useful synthetic intermediates, this provided the unique opportunity to functionalize the basic skeleton at two different positions.