Synthesis and characterization of boronates derived from non-symmetric amino-bis-phenols

The condensation of 2-[[(2-hydroxyphenyl)amino]methyl]-phenols (1a–1e) with different arylboronic acids led to 12 new monomeric boronates of the type 2-aryl-dibenzo[d,h]-6-aza-1,3-dioxa-2-boracyclononene (2a–2l). The boronates were characterized by 1H-, 13C-, 11B- and 2D-NMR experiments, FT infrared, mass spectra and elemental analyses. The stereochemistry of the H–N → B–Ph fusion is always cis, as established through the NMR spectra, as well as the X-ray structures of four boronates (2a, 2e, 2f and 2l). Hydrogen bonds between the amine proton and the oxygen ester of the five- membered ring are present in three X-ray structures (2a, 2e and 2f), while the supramolecular structure in the derivative possessing a primary amine (2l) is built up through the protons present in this moiety instead of the proton from the H–N → B–Ph fragment.