1,3-Bis(O-cyanomethyl)-p-tert-butylthiacalix[4]arene (5) has been found to interconvert between syn and anti conformations in solution. The equilibrium shifts toward the anti form with increasing solvent polarity. In the solid state, it adopts a pinched cone conformation with the syn arrangement of the cyanomethyl groups. Reduction of the equilibrium mixture of 5 with LiAlH4 gives only anti stereoisomer of 1,3-bis(O-amino-ethyl)-p-tert-butylthiacalix[4]arene.