Structure of Geminal Diol–Type Intermediates and Their Reactivity in Modern Oxidation Reactions

Geminal diol ( gem ‐diol) moieties commonly exist in equilibrium with ketones or aldehydes when water is present in the system. While significant progress has been made in their structural characterization, recent studies have increasingly focused on the reactivity of gem ‐diol intermediates. In parallel, gem ‐diol‐type hydroxyl‐oxoammonium species have been reported as key intermediates in various reactions. Accordingly, this concept highlights recent advances in the structural elucidation of gem ‐diol‐type intermediates and, more importantly, discusses their reactivity and potential application in organic reactions. In addition to typical gem ‐diol species, the discussion also encompasses other gem ‐diol‐type species with OC(sp 3 )O or ON(sp 3 )O centers derived from C(sp 2 )O or N(sp 2 )O centers, respectively. The ultimate aim is to inspire the development of more efficient strategies for employing such gem ‐diol‐type intermediates in organic synthesis.