A tautomeric equilibrium between functionalized 2-formylphenylboronic acids and corresponding 1,3-dihydro-1,3-dihydroxybenzo[c][2,1]oxaboroles†‡
Abstract
Functionalized 2-formylphenylboronic acids undergo an unprecedented tautomeric rearrangement in solution to form corresponding 1,3-dihydro-1,3-dihydroxybenzo[c][2,1]oxaboroles. X-Ray analyses of selected examples revealed diverse solid-state molecular structures from a planar open form with a hydrogen-bonded carbonyl group (X = 3-F) through a twisted conformer showing a weak carbonyl–boron interaction (X = 3,5-Br2) to a cyclic oxaborole derivative (X = 3-Br). Variable-temperature 1H NMR spectroscopy was used to determine equilibrium constants as well as enthalpies and entropies of