Pinacol Coupling Reaction
This reaction involves the reductive homo-coupling of a carbonyl compound to produce a symmetrically substituted 1,2-diol. The first step is single electron transfer of the carbonyl bond, which generates radical ion intermediates that couple via carbon-carbon bond formation to give a 1,2-diol. The example depicted above shows the preparation of pinacol itself.
Pinacol and other highly substituted 1,2-diols tend to undergo dehydration with rearrangement under acid-catalysis (see Pinacol Rearrangement).
Catalytic, Highly Enantio- and Diastereoselective Pinacol Coupling Reaction with a New Tethered Bis(8-quinolinolato) Ligand
N. Takenaka, G. Xia, H. Yamamoto, J. Am. Chem. Soc., 2004, 126, 13198-13199.
A highly enantioselective catalytic protocol for the intramolecular reductive coupling of ketones and hydrazones furnishes cyclic syn 1,2-amino alcohol derivatives with excellent levels of diastereo- and enantioselectivity. The reaction proceeds through neutral ketyl radical intermediates generated via a concerted proton-coupled electron transfer event jointly mediated by a chiral phosphoric acid catalyst and a photoredox catalyst.
L. J. Rono, H. G. Yayla, D. Y. Wang, M. F. Armstrong, R. R. Knowles, J. Am. Chem. Soc., 2013, 135, 17735-17738.
A Convenient Synthesis of Unsymmetrical Pinacols by Coupling of Structurally Similar Aromatic Aldehydes Mediated by Low-Valent Titanium
X.-F. Duan, J.-X. Feng, G.-F. Zi, Z.-B. Zhang, Synthesis, 2009, 277-282.
Samarium(II)-Mediated Pinacol Coupling in Water: Occurrence of Unexpected Disproportionation and Action of Low-Valent Samarium as an Active Species
S. Matsukawa, Y. Hinakubo, Org. Lett., 2003, 5, 1221-1223.