Wittig-Horner Reaction
Horner-Wadsworth-Emmons Reaction

The reaction of aldehydes or ketones with stabilized phosphorus ylides (phosphonate carbanions) leads to olefins with excellent E-selectivity.

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Mechanism

The reaction mechanism is similar to the mechanism of the Wittig Reaction. The stereochemistry is set by steric approach control, where the antiperiplanar approach of the carbanion to the carbon of the carbonyl group is favored when the smaller aldehydic hydrogen eclipses the bulky phosphoranyl moiety. This places the ester group syn to the aldehyde R group, but the incipient alkene assumes an E-orientation of these groups after rotation to form the oxaphosphetane. As the lithium counterion does not interfere with oxaphosphetane formation, use of BuLi is possible, but NaH and NaOMe are also suitable bases for forming the ylide. The resulting phosphate byproduct is readily separated from the desired products by simply washing with water.

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Recent Literature

Generation of Phosphoranes Derived from Phosphites. A New Class of Phosphorus Ylides Leading to High E Selectivity with Semi-stabilizing Groups in Wittig Olefinations
V. K. Aggarwal, J. R. Fulton, C. G. Sheldon, J. de Vicente, J. Am. Chem. Soc., 2003, 125, 6034-6035.

Mild Zinc-Promoted Horner-Wadsworth-Emmons Reactions of Diprotic Phosphonate Reagents
D. J. Schauer, P. Helquist, Synthesis, 2006, 3654-3660.

Stereoselective Preparation of (E)-α-Bromoacrylates from Mixtures of Brominated Ando Phosphonates
T. Olpp, R. Brückner, Synthesis, 2004, 2135-2152.

Tandem Horner-Wadsworth-Emmons Olefination/Claisen Rearrangement/Hydrolysis Sequence: Remarkable Acceleration in Water with Microwave Irradiation
E. Quesada, R. J. K. Taylor, Synthesis, 2005, 3193-3195.

A Convenient Method for the Synthesis of Terminal (E)-1,3-Dienes
Y. Wang, F. G. West, Synthesis, 2002, 99-103.

Reliable and Versatile Synthesis of 2-Aryl-Substituted Cinnamic Acid Esters
A. Ianni, S. R. Waldvogel, Synthesis, 2006, 2103-2112.

Synthesis of Vinyl Sulfonamides Using the Horner Reaction
D. C. Reuter, J. E. McIntosh, A. C. Guinn, A. M. Madera, Synthesis, 2003, 2321-2324.

One-Pot Homolytic Aromatic Substitutions/HWE Olefinations under Microwave Conditions for the Formation of a Small Oxindole Library
A. Teichert, K. Jantos, K. Harms, A. Studer, Org. Lett., 2004, 6, 3477-3480.