Synthesis, characterization and X-ray studies of new six–seven membered rings [4.5.0] heterobicyclic system of monomeric boronates

Different tridentate ligands derived from ethanolamines and 2-hydroxyacetophenone, 2-hydroxybenzophenone and salicylaldehyde were reacted with two equivalents of phenylboronic acid to obtain compounds 6a–6f which are [4.5.0] heterobicyclic systems with a B−O−B structural unit. The boronates were fully characterized and two heterobicyclic [4.5.0] structures have been analyzed by X-ray crystallography, where a series of parameters such as bond distances, bond angles, torsion angles, tetrahedral character at the boron atom and deviation of the boron atom from the mean plane have been evaluated.

Graphical abstractReaction of tridentate ligand 2-[1-(2-hydroxy-propylimino)-ethyl]-phenol with two equivalents of phenyl boronic acid in toluene during 1 h give place to the synthesis of the monomeric boronate 6a with a [4.5.0] heterobicyclic system.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Heterobicyclic systems with a B−O−B structural unit. ► Formation of a new chiral center at the boron atom. ► The conformation in the seven member ring in molecules obtained is chair. ► The structure of boron compounds were analyzed by X-ray diffraction. ► Boronates with fused six–seven membered rings are very stable.