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.

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.