Synthesis, characterization and X-ray studies of new chiral five-six-membered ring, [4.3.0] heterobicyclic system of monomeric boronates

Nine new boronates, six of them chiral, with five-six-membered ring heterobicycles were prepared by reaction of the Schiff bases and phenyl boronic acid. The boronates were fully characterized by spectroscopic techniques, NMR 1H, 13C, 11B, Infrared spectroscopy, mass spectrometry and elemental analysis. The reaction showed high diasteroselectivity, only in the case of compound 4c, containing a methyl substituent in the aliphatic moiety, the induction is low giving a 2:1 mixture of two diatereoisomers. The results showed that the preferred stereochemistry in the heterocycles is that where all substituents in the five membered ring and the phenyl group attached to boron atom are on the same side.

Reaction of tridentate ligand 2-[1-(2-Hydroxy-1-methyl-2-phenyl-ethylimino)-ethyl]-phenol with phenyl boronic acid in toluene during 24 h. give place to the synthesis of the monomeric boronate 4a with a [4.3.0] heterobicyclic system.Figure optionsDownload as PowerPoint slideHighlights
► Five-six-membered ring boron heterobicycles synthesis.
► Formation of a new chiral center at the boron atom with high diasteroselectivity.
► Low values for the tetrahedral character (THC) at boron atom.
► Envelope conformation in the five member ring.
► Ring opening because of the high strain in the five membered ring.
► Possible applications as chiral inductors.