Synthesis and Structure of Functionalized Homo Heteracalix[2]arene[2]triazines: Effect of All Heteroatom Bridges on Macrocyclic Conformation

A number
of unprecedented homo heteracalix[2]­arene[2]­triazines
were synthesized by means of a fragment coupling approach. Two directional
nucleophilic substitution reactions of N-Boc-protected
1,3-dihydrazobenzene with cyanuric acid chloride and 2-butoxy-4,6-dichloro-1,3,5-triazine
led to hydrazo-linked trimers, which underwent an efficient macrocyclic
condensation reaction with functionalized resorcinol derivatives to
afford (NHNBoc)2,O2-calix­[2]­arene­[2]­triazine
macrocycles, which contain a functional group either on the upper
rim or the lower rim. The use of 1,3-phenylenediamines instead of
resorcinol in the reaction produced (NR)2,(NHNBoc)2-calix­[2]­arene­[2]­triazines. Postmacrocyclization modifications
such as a nucleophilic substitution reaction of chloro on triazine
by amines and the removal of Boc from hydrazo moieties produced homo
calix[2]­arene[2]­triazine derivatives. In the solid state, (NHNR)2,O2-bridged calix[2]­arene[2]­triazines with and
without a substituent on the upper rim position and (NMe)2,(NHNBoc)2-calix­[2]­arene­[2]­triazine adopted a typical
partial cone conformation while the heavily twisted 1,3-alternate
conformational structures were observed for both (NHNBoc)2,O2-calix­[2]­arene­[2]­triazines bearing a functional group
on the lower rim position and (NH)2,(NHNBoc)2-calix­[2]­arene­[2]­triazine. In solution, all synthesized homo heteracalix[2]­arene[2]­triazines
existed as the mixture of different macrocyclic conformers, which
underwent slow interconversions at room temperature relative to the
NMR time scale.