Synthesis of (NH)(m)(NMe)(4-m)-bridged calix[4]pyridines and the effect of NH bridge on structure and properties.
The (NH)(m)(NMe)(4-m)-bridged calix[4]pyridines (m = 1-4) 19-23 were synthesized in excellent yields from deprotection of N-allyl groups of (NAllyl)(m)(NMe)(4-m)-bridged calix[4]pyridine derivatives 8 and 15-18, which were prepared in moderate yields by macrocyclic 2+2 and 1+3 coupling reactions 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 to mainly the formation of varied conjugation systems of bridging NH units with their neighboring pyridines. In solution, all (NH)(m)(NMe)(4-m)-bridged calix[4]pyridines were very fluxional and the rates of interconversion of various conformational structures were very rapid relative to the NMR time 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 recognition of zinc(II) ion in solution with the dramatic enhancement of fluorescence intensity.
Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
En-Xuan
EX
Zhang
De-Xian
DX
Wang
Zhi-Tang
ZT
Huang
Mei-Xiang
MX
Wang
D003500:Cyclization; D015394:Molecular Structure; D011725:Pyridines / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
D011725:Pyridines