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).

Recent Literature

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.

Zn/InCl₃-Mediated Pinacol Cross-Coupling Reactions of Aldehydes with α,β-Unsaturated Ketones in Aqueous Media
Y.-S. Yang, Z.-L. Shen, T.-P. Loh, Org. Lett., 2009, 11, 2213-2215.

Samarium Diiodide-Catalyzed Diastereoselective Pinacol Couplings
H. C. Aspinall, N. Greeves, C. Valla, Org. Lett., 2005, 7, 1919-1922.

Reduction and Coupling Reactions of Carbonyl Compounds Using Samarium Metal in Aqueous Media
S. Talukdar, J.-M. Fang, J. Org. Chem., 2001, 66, 330-333.

TiCl₄-n-Bu₄NI as a Reducing Reagent: Pinacol Coupling and Enolate Formation from α-Haloketones
T. Tsuritani, S. Ito, H. Shinokubo, K. Oshima, J. Org. Chem., 2000, 65, 5066-5068.

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.

Novel and efficient Ni-mediated pinacol coupling of carbonyl compounds
L. Shi, C.-A. Fan, Y.-Q. Tu, M. Wang, F.-M. Zhang, Tetrahedron, 2004, 60, 2851-2855.