Synthesis of (NH)m(NMe)_(4-m)-Bridged Calix[4]pyridines and the Effect of NH Bridge on Structure and Properties

摘要

The (NH)_m(NMe)_(4-m)-bridged calix[4]pyridines (m = 1-4) 19-23 were synthesized in excellentyields from deprotection of N-allyl groups of (NAlly1)_m(NMe)_(4-m)-bridged calix[4]pyridine deriva-tives 8 and 15-18, which were prepared in moderate yields by macrocyclic 2+2 and 1+3 couplingreactions between simple diamino- and dibromo-substituted fragments. In the solid state,(NH)_m(NMe)_(4-m)-bridged calix[4]pyridines adopted different 1,3-alternate conformations due tomainly the formation of varied conjugation systems of bridging NH units with their neighboringpyridines. In solution, all (NH)_m(NMe)_(4-m)-bridged calix[4]pyridines were very fluxional and therates of interconversion of various conformational structures were very rapid relative to the NMRtime scale. While (NH)_4-bridged calix[4]pyridine 23 formed the strongest conjugation system,(NH)_2(NMe)_2-bridged calix[4]pyridine 21 acted as a selective fluorescence probe in the recognitionof zinc(II) ion in solution with the dramatic enhancement of fluorescence intensity.