3-(Dimethylboryl)pyridine: synthesis, structure, and remarkable steric effects in scrambling reactions.
A facile method for the synthesis of 3-(dimethylboryl)pyridine (1a) is described. Compound 1a assembles into a rigid cyclic tetramer stabilized via intermolecular boron-nitrogen coordination bonds both in the crystalline state and in solution. The outstanding structural feature of 1a, as compared with previously reported 3-(diethylboryl)pyridine (2a) (which adopts a cone conformation), is that the tetramer of 1a adopts a 1,2-alternate conformation. To investigate the effect of substituents at the boron atom on the stabilities of the oligomers, scrambling experiments of the component molecules using 1, 2, and 3-(di-n-butylboryl)pyridines 3 were carried out. Although heating at 80-90 degrees C for 20 h was required to attain the equilibrium of the scrambling reactions when the component molecules of the tetramers were 2 or 3, the scrambling in 1 proceeded under relatively mild conditions (60 degrees C, 3 h). This difference in reaction conditions required for 1, as compared to conditions required for 2 or 3, could not be explained solely by the stabilities based on bond lengths or THC. It appears that whereas only an S(N)1-type pathway may be involved in the scrambling of 2 or 3, both S(N)1- and S(N)2-type mechanisms operate simultaneously during scrambling reactions of 1 or an intermediate mechanism between S(N)1 and S(N)2 operates, which was supported by kinetic studies and calculations using model compounds.
Department of Clinical Nutrition, Faculty of Health Science, Suzuka University of Medical Science, Suzuka, Mie 510-0293, Japan. s-waka@suzuka-u.ac.jp
Shigeharu
S
Wakabayashi
Saori
S
Imamura
Yoshikazu
Y
Sugihara
Makoto
M
Shimizu
Toshikazu
T
Kitagawa
Yasuhiro
Y
Ohki
Kazuyuki
K
Tatsumi
D001896:Boron Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D015394:Molecular Structure; D011725:Pyridines / Q000138:chemical synthesis* / Q000737:chemistry*; D013237:Stereoisomerism
C527310:3-(dimethylboryl)pyridine; D001896:Boron Compounds; D011725:Pyridines