Structural Requirements of 1-(2-Pyridinyl)-5-pyrazolones for Disproportionation of Boronic Acids

Abstract

We observed an unusual formation of four-coordinate boron(III) complexes from the reaction of 1-(2-pyridinyl)-5-pyrazolone derivatives with arylboronic acids in the basic media. The exact mechanism is not clear; however, the use of unprotected boronic acid and the presence of a bidentate ligand appeared to be the key structural requirements for the transformation. The results suggest that base-promoted disproportionation of arylboronic acid with the assistance of the [N,O]-bidentate ligation of 1-(2-pyridinyl)-5-pyrazolone should take place and facilitate the formation of pyrazole diarylborinate. Experiments to obtain a deeper understanding of its mechanism are currently underway.

Steric and Electronic Effects Responsible for N,O- or N,N-Chelating Coordination of Pyrazolones Containing a Pyridine Ring in Ruthenium Arene Systems

“…The proligand HL py,ph with binding potential has been previously reported by others, − and its crystal structure solved by Watkins et al, but its coordinating ability toward metal ions is still unexplored. Moreover, we have introduced 1,3,5-triaza-7-phosphaadamantane (PTA) phosphine in the ruthenium environment by replacing the chloride ligand, affording cationic complexes with the aim to improve solubility in water.…”

“…The proligand HL py,ph was synthesized with a different procedure from those reported in the literature, − which increases its yield. HL py,ph was synthesized by reacting equimolar amounts of 2-hydrazineylpyridine (2.29 g, 21 mmol), and ethyl 3-oxo-3-phenylpropanoate (4.04 g, 21 mmol) at room temperature.…”

Special Issue “Recent Advances in the Synthesis, Functionalization and Applications of Pyrazole-Type Compounds II”

“…Lee and coworkers revealed the key structural requirements of 1-(2-pyridinyl)pyrazol-5-ones for disproportionation of boronic acids, which are the use of unprotected acid and the presence of a [N,O]-bidentate ligand. Although the exact mechanism of this disproportionation is not clear, the reported method is particularly important for the synthesis of four-coordinate organoboron species to ensure a completely efficient assembly of multi-component structures in a single operation [7]. Pyrazolopyridines are among the most studied condensed pyrazole systems in medicinal chemistry.…”