Structure and Properties of 3-(Diethylboryl)pyridines1

• Published in: Journal of organic chemistry Vol. 61; no. 20; pp. 6829 - 6834
• Main Authors: Sugihara, Yoshikazu, Takakura, Katsuto, Murafuji, Toshihiro, Miyatake, Ryuta, Nakasuji, Kazuhiro, Kato, Masako, Yano, Shigenobu
• Format: Journal Article
• Language: English
• Published: American Chemical Society 04.10.1996
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo960825k

3-(Diethylboryl)pyridine (1a), a versatile starting material for the preparation of arylpyridines, is notable for its stability under ambient conditions, in spite of little steric hindrance on the boron atom. 1H and 13C spectra of 1a indicated that the boryl group does not act as a mere π-acceptor and that the boron atom is shielded by ca. 50 ppm even when compared with trivalent boron atoms conjugated with the π-donor. A single-crystal X-ray crystallographic study for 1a revealed formation of a cyclic-tetramer with a void via the intermolecular boron−nitrogen coordination bond. Vapor pressure osmometry in various solvents suggested that 1a comprises the tetramer in these solutions. In order to know the actual structure, synthesis of 3-(2-methoxyethoxy)-5-(diethylboryl)pyridine (1b) and its scrambling experiment with 1a were carried out. Heating at 100 °C for 24 h was required to attain the equilibrium of the scrambling of the component molecules in the tetramers. This means that 3-(diethylboryl)pyridines 1a and 1b comprise the rigid cyclic-tetramer in solution at ambient temperature. Compound 1b is stable in aerated tetrahydrofuran containing up to 33 % water.