Synthesis and Structural Characterization of Diazulenylborinic Acid
T. Murafuji, K. Shintaku, K. Nagao, Y. Mikata, K. Ishiguro, S. Kamijo
Heterocycles, 2017, 94, 2676-690.
DOI: 10.3987/COM-17-13651

Abstruct: Diazulenylborinic acid 1 was synthesized by the reaction of 1,3-dibromoazulen-2-yllithium (2) with 1,3-dibromoazulen-2-ylboronic acid ethylene glycol ester (7d). The X-ray crystallographic study of 1 revealed that it forms a dimeric structure through intermolecular hydrogen bonding between the hydroxyl groups. To obtain the tetracoordinate borinate derivative from 1, the attempted esterification of 1 with N,N-dimethylethanolamine did not give corresponding borinate 8 but resulted in the unexpected protodeboronation to give parent 1,3-dibromoazulene (4). The 13C and 11B NMR studies of 1 in the presence of Et3N revealed the change in the π-polarization of the azulenyl group accompanied by the change in the geometry of the boron to a tetracoordinate structure.