The Benzoin Condensation Is A Coupling Reaction Between Two Aldehydes That Allows The Preparation Of α-hydroxyketones. The First Methods Were Only Suitable For The Conversion Of Aromatic Aldehydes.
Addition Of The Cyanide Ion To Create A Cyanohydrin Effects An Umpolung Of The Normal Carbonyl Charge Affinity, And The Electrophilic Aldehyde Carbon Becomes Nucleophilic After Deprotonation: A Thiazolium Salt May Also Be Used As The Catalyst In This Reaction (see Stetter Reaction).
A Strong Base Is Now Able To Deprotonate At The Former Carbonyl C-atom:
A Second Equivalent Of Aldehyde Reacts With This Carbanion; Elimination Of The Catalyst Regenerates The Carbonyl Compound At The End Of The Reaction:
Recent Literature
Chemoselective N-Heterocyclic Carbene-Catalyzed Cross-Benzoin Reactions: Importance Of The Fused Ring In Triazolium Salts
S. M. Langdon, M. M. D. Wilde, K. Thai, M. Gravel, J. Am. Chem. Soc., 2014, 136, 7359-7542.
Lanthanum Tricyanide-Catalyzed Acyl Silane-Ketone Benzoin Additions
J. C. Tarr, J. S. Johnson, Org. Lett., 2009, 11, 3870-3873.
Kinetic Control In Direct α-Silyloxy Ketone Synthesis: A New Regiospecific Catalyzed Cross Silyl Benzoin Reaction
X. Linghu, J. S. Johnson, Angew. Chem. Int. Ed., 2003, 42, 2534-2536.
Highly Enantioselective Benzoin Condensation Reactions Involving A Bifunctional Protic Pentafluorophenyl-Substituted Triazolium Precatalyst
L. Baragwanath, C. A. Rose, K. Zeitler, S. J. Connon, J. Org. Chem., 2009, 74, 9214-9217.
An Efficient Nucleophilic Carbene Catalyst For The Asymmetric Benzoin Condensation
D. Enders, U. Kallfass, Angew. Chem. Int. Ed., 2002, 41, 1743-1745.
Highly Chemo- And Enantioselective Cross-Benzoin Reaction Of Aliphatic Aldehydes And α-Ketoesters
K. Thai, S. M. Langdon, F. Bilodeau, M. Gravel, Org. Lett., 2013, 15, 2214-2217.
Asymmetric Intramolecular Crossed-Benzoin Reactions By N-Heterocyclic Carbene Catalysis
D. Enders, O. Niemeier, T. Balensiefer, Angew. Chem. Int. Ed., 2006, 45, 1463-1467.