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Synthetic strategies for self-assembled schiff-base macrocycles Provençal, Alexandre

Abstract

Schiff-base macrocycles have interesting properties that could be used in new materials such as chemical sensors, catalysts and discotic liquid crystals. Triangular [3+3] Schiff-base macrocycles, for example, have been extensively studied in the MacLachlan group. However, few examples of [4+4] Schiff-base macrocycles have been reported. A square [4+4] Schiff-base macrocycle requires a precursor with the appropriate geometry such as compound 18. Synthesis of compound 18, however, proved to be problematic because of the formation of isomers, poor solubility and low yields. To avoid these issues, compound 36 was synthesized by Sonogashira coupling and was characterized by ¹H NMR spectroscopy, IR spectroscopy and HR-EI-MS. Reaction between compounds 36 and 37 led to the formation of an insoluble red solid. Although the characterization of this solid by NMR spectroscopy was not possible, MALDI-TOF data suggested that this solid contained the [4+4] Schiff-base macrocycle as the major product. A new synthetic approach to compound 11, widely used for the formation of [3+3] Schiff-base macrocycles, was devised. The overall yield is about 10% higher than the original synthesis of compound 11. Aside from the higher yield, this synthetic approach has other advantages over the previous one such as it does not require a large excess of reagents or expensive chemicals, all steps can be achieved on large scales and little purification between each step is required. All new intermediates were characterized by ¹H NMR spectroscopy, ¹³C NMR spectroscopy, IR spectroscopy and HR-EI-MS.

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