Functionalization of the methylene groups of p-tert-butylcalix[4]arene: S-C, N-C, and C-C bond formation

Reaction of the calixarene derivative 7 with two exocyclic double bonds with carbon-, nitrogen-, oxygen-, or sulfur-containing nucleophiles afforded bis(spirodienone) derivatives substituted at two opposite methylene groups in a trans fashion. LiAlH₄ reduction of the bis(spirodienone) derivatives with two methylenes functionalized by thiomethoxy, diethyl malonate, or anilino substituents yielded trans methylene-substituted calix[4]arenes. Upon standing in solution, the calixarene derivative incorporating SMe groups on the bridges underwent trans ⇌ cis isomerization. An equilibration study performed on this calixarene derivative (tetrachloroethane-d₂, 430 K) indicated that the cis isomer is the form of lower free energy.