Synthesis, Structure, and Reactions of NH-Bridged Calix[m]arene[n]pyridines

Abstract

NH-bridged calix[1]arene[3]pyridine and calix[2]arene[2]pyridine were synthesized readily from efficient deprotection of N-Boc groups of NBoc-bridged calix[m]arene[n]pyridine derivatives which were prepared by a macrocyclic coupling reaction between NBoc-linked trimers and 1,3-phenylenediamine. In the solid state, calix[2]arene[2]pyridine adopted the flattened saddle conformation, while NH-bridged calix[1]arene[3]pyridine gave a slightly twisted 1,3-alternate conformer. In both cases, all NH bridges formed partial conjugation with both pyridine and benzene rings, whereas in solution they gave symmetric conformational structures in which the conjugation of bridging NH units with pyridine ring was stronger than with benzene ring. In the presence of NaH, NH-bridged calix[2]arene[2]pyridine reacted efficiently with methyl iodide and allyl bromide to afford the corresponding N-alkylated products in almost quantitative yield. Upon treatment of NH- and NMe-bridged calix[2]arene[2]pyridines with CF3CO2D and CuBr2, deuteration and bromination reactions took place selectively on the pyridine ring, producing respectively the pyridine ring-deuterated and -brominated macrocyclic products.