The title compounds I to 6 (Table 1) are shown by 'H, "B, and I5N NMR shifts t o form an intramolecular B -N bond which, according to 'H and I3C NMR, is frequently broken (AG: = 40 to 54 kJ/mol, Table 2) and re-formed.
Rasche thermische Offnung und SchlieDung einer B -N-Bindung in t(Aminome1hyl)benzolboronaten 1)'H-, "B-und '5N-NMR-Ver~chiebungen weisen darauf hin, dafl die Titelverbindungen 1 -6 (Tab. 1) eine intramolekulare B -N-Bindung ausbilden, die laut 'H-und I3C-NMR mit hoher Frequenz gedffnet (AG: = 40 bis 54 kJ/mol, Tab. 2) und wieder geschlossen wird.Boronic acid groups were used as the binding sites at enzyme-analogue built polymers for the specific binding of d i~l s * .~) .Binding of the diols to these polymers occurs on formation of cyclic boronic diesters in an equilibrium reaction. Enhancement of the rate of such equilibration should improve the binding properties of the boronic acid. It was also considered desirable to fix the steric arrangement of the boronic acid by hindrance to rotation around the B -C axis. Investigations along these lines were first performed with low molecular weight analogues, where it was shown that the introduction of N(CH,), as a neighbouring group to the boronic ester function enhanced by several orders of magnitude4) the. rate of establishing the above equilibrium in areneboronates like 1 (Table 1). Therefore, the occurrence of a B -N bond in such compounds in solution and the kinetic stability of this bonds were investigated.Is), (4S)-2, 3, (4R)-4, and 5 (Table 1) were prepared by esterification of 2-(dimethylaminomethyl)benzeneboronic anhydride') with the corresponding 1,2-diols. Similarly, the known 2-tolueneboronic anhydride was converted to 7, (4S)-8, 9, and (4RS)-10. 6, an ester of a new areneboronic acid, was synthesized from 2-[2-(bromomethyl)phenyl]-1,3,2-dioxaborolane and isoindoline.The NCH, and NCH, proton-NMR signals of 1 to 5 are shifted to lower field by A 6 = +0.3 to +0.6 relative to the corresponding signals of the boron-free amine 11
