Stepwise Construction of Some Hexahomooxacalix[3]arenes and Their Conformations in Solid State

Hexahomooxacalix[3]arenes 1 bearing different substituents on their upper rim were synthesized from the corresponding linear trimers 2 by the acid-catalyzed cyclization. The X-ray crystallographic analyses of 1 (R 1 = R 3 = H, R 2 = t -Bu, and R 1 = Et, R 2 = t -Bu, R 3 = i -Pr) revealed that they adopt a cone conformation, owing to an intramolecular hydrogen-bonded network in the solid state.