Synthesis of a Novel Class of Aza Crown Macrocycles Containing Two 1,2,4-Triazole Rings as Subunits

摘要

Since Pedersen's discovery of crown ethers and their abilities to bind strongly with metal ions in 1967, the study of crown ethers has grown at an incredible rate. The syntheses of many different types of crown ethers, e.g., crown ether diesters, aza crown ethers, thiacrown ethers, and chiral crown ethers, have been documented in the literature and their binding properties such as binding selectivity and strength toward a wide range of metal ions, non-metal ions, and neutral molecules have been investigated. The incorporation of oxygen, nitrogen and sulfur donor atoms in the macrocycles will also markedly affect their complexing properties because of the hard (O, N) and soft (S) character of the donor atoms and the exodentate tendency of the sulfide linkages. In connection with these findings and in continuation of our interest in synthesizing macrocyclic crown compounds containing heterocyclic moieties, we report here the synthesis of a series of 18-21 membered aza crown macrocycles fused with two 1,2,4-triazole rings containing N, O inside the macrocyclic ring as donor atoms. The synthesis of azacrown ethers containing 1,2,4-teriazole rings has not been reported yet. The synthetic strategy includes the cyclocondensation between bis aminotriazoles and the appropriate bis-aldehydes, to give the corresponding Schiff bases. The starting 1,2-bis(4-amino-5-mercapto-4H-1,2,4-triazol-3-yl)alkane 1a-c was prepared by heating aliphatic diacid with two molar equivalents of carbonothioic dihydrazide in an oil bath at 170 C. Reaction of 1,2-bis(4-amino-5-mercapto-4H-1,2,4-triazol-3-yl)alkanes la-c with equivalents of each of bis-aldehydes 2a-c in refluxing acetic acid under the high dilution conditions afforded the corresponding aza crown ether compounds 3a-h (Scheme 1).