Oxidative Deboronation of Organic Boron-Containing Molecules by Oxidants HOX or Oxygen: Computational Mapping of Mechanistic Alternatives

Abstract

Oxidative deboronation of boron-containing organic species is of wide interest, particularly because of their applications in synthetic routes and biological settings. Two types of oxidation are important and have been studied computationally, as reported herein: 1) reaction with oxidants HOX (X = leaving group), which are commonly employed to achieve B-to-O exchange in synthetic applications and occur under physiological conditions, and 2) reaction with oxygen in air, which, with triethylborane BEt3, is a well-established radical initiation approach. In the reactions with HOX, the prevalent emphasis on a tetrahedral anionic intermediate and its transformation into oxidized products is generally supported by theory, but changes in mechanism should be expected as conditions are varied, particularly concentration, pH, and solvent. The most extreme such change is the transition to radical reactions, which has implications for the safety of reactions and of species administered in vivo and is particularly likely for borinic acids. For autoxidation, theory does not support initiation by oxygen, but trace ozone in air would be a competent initiator.