Macrocycles, adducts and monomeric boron compounds derived from 2,6-dimethanolpyridine and arylboronic acids

The reaction of 2,6-dimethanolpyridine with arylboronic acids at room temperature led to the formation of tetrameric compounds 1a–1e in good yields. Since the tetrameric derivatives were insoluble in common organic solvents, their characterization was based on IR, mass spectrometry, as well as 13C and 11B NMR, in the solid state. Macrocyclic compounds 1a–1e can be hydrolyzed upon heating in DMSO to give adducts 2a–2e, which are only held by a coordination bond between the nitrogen and boron atoms, as demonstrated by 1H, 13C and 11B NMR, in solution. Moreover, the presence of an additional carbon atom in the aliphatic chain of the ligand, as in the case of 2,6(β-diethanolamine)pyridine, leads exclusively to the formation of the monomeric specie 4, as established by X-ray diffraction analysis.