Horner-Wadsworth-Emmons reaction modification

Horner-Wadsworth-Emmons Reactions of Phosphonate Anions. - As with the Horner modification of the Wittig reaction, the principal focus of papers that mention the Horner-Wadsworth-Emmons reaction relate to synthetic applications. The use of pressure to induce the synthesis of P-amino esters, p-thioesters and P-thionitriles via tandem Horner-Wadsworth-Emmons and Michael reactions has been reported. The reagent (l-tritylimidazol-4-yl)methylphosphonate (99) has been prepared and, when treated with aldehydes and ketones, affords (E)-vinylimidazoles in high yields. ... 

Ando Modification of the Horner-Wadsworth-Emmons Reaction... 

The Horner-Wadsworth-Emmons modification of the Wittig reaction continues to find wide application in contemporary organic synthesis. Two reviews, looking at different aspects of the stereoselectivity of this procedure, have been published. One considers approaches to improve the Z-selectivity of the Horner-Wadsworth-Emmons reaction, and the other the use of heteroatoms to improve the stereoselectivity of the Horner-Wadsworth-Emmons reaction. A combined experimental and computational study of the selectivity of the Horner-Wadsworth-Emmons reaction of a series of phosphonoacetates (172) has... 

Some of the disadvantages of the Wittig reaction can be overcome by use of the Horner-Wadsworth-Emmons reaction or, in brief, the Horner-Emmons reaction [6,14-16]. The modification of the Wittig process makes use of a phosphonate-stabilized carbanion instead of a phosphorus ylide it is discussed in Section E. 

An important modification (often called the Horner-Wadsworth-Emmons reaction) of fhe Wiffig reaction makes use of phosphonate esters, RP0(0R )2- It is highly stereoselective for the formation of E-alkenes.The reaction and mechanism are depicted below for the preparation of (E)-stilbene. Instead of using a phosphorus cation to stabilize the negative charge, as in the phosphonium ylide above, a phosphonate ester group is used to stabilize an adjacent carbanion. 

Maercker, A. The Wittig Reaction Organic Reactions 1965, 14, 270-490. Maryanoff, B. E. Reitz, A. B. The Wittig Olefmation Reaction and Modifications Involving Phosphoryl-Stabilized Carbanions. Stereochemistry, Mechanism, and Selected Synthetic Aspects Chemical Reviews 1989, 89, 863-927. Blanchette, M. A. Choy, W. Davis, J. T. Essenfeld, A. P. Masamune, S. Roush, W. R. Sakai, T. Horner-Wadsworth-Emmons Reaction Use of Lithium Chloride and an Amine for Base-Sensitive Compounds Tetrahedron Lett. 1984, 25, 2183-2186. 

Step 1 (3-keto phosphonates often are used for olefmation of ketones (Horner-Wadsworth-Emmons modification of the Wittig reaction). Steps 2 + 3 The cuprate-mediated 1,4-addition and subsequent Lemieux-Johnson oxidation of a vinyl group are excellent procedures for the introduction of the p-formyl group. 

Horner-Wadsworth-Emmons (HWE) reaction There is a close relationship between the original Wittig alkenation and its phosphonate ester modification which is known as... 

Related reactions , Horner-Wadsworth-Emmons olefination - Still-Gennari modification, Julia-Lithgoe olefination, Peterson... 

Related reactions Horner-Wadsworth-Emmons olefination, Homer-Wadsworth-Emmons olefination - Still-Gennari modification, Julia-Lithgoe olefination, Takai-Utimoto olefination, Tebbe oiefination, Wittig reaction, Wittig reaction - Schiosser modification ... 

Related reactions Horner-Wadsworth-Emmons olefination, Horner-Wadsworth-Emmons oiefination - Stiii-Gennari modification,... 

The past year has seen continued interest in the structural nature of phosphorus ylides with the aim of gaining greater insight into their stabilities, electronic distributions and conformations, which ultimately affect the reactivities of these species. However, there have been fewer mechanistic studies of the Wittig reaction itself although several studies into the closely related aza-Wittig and Horner-Wadsworth-Emmons modifications have appeared. 

Purpose To demonstrate the synthesis of a stilbene by the Horner-Wadsworth-Emmons modification of the Wittig reaction. 

The use of the phosphonate ester (Homer-Wadsworth-Emmons reaction) allows much easier separation of the product alkene, since the sodium phosphate byproduct is water soluble the byproduct of fhe Wiffig reaction, tri-phenylphosphine oxide, is not water soluble. In the Horner-Wadsworth-Emmons modification, a conjugated, or electron-withdrawing, substituent (such as a phenyl or carbonyl group) on the nucleophilic carbon is used to assist in the stabilization of the carbanion. This modification (Experiment [19B]) maybe used as an alternative to Experiment [19A] for the preparation of (E)-stilbene. The "instant-ylide" Wittig reaction yields predominantly the E isomer of... 

THE HORNER-EMMONS OR WADSWORTH-EMMONS MODIFICATION OF THE WITTIG REACTION... 

The synthetic utility of lithium salts of (l-methylthio)alkylphosphonate esters for the preparation of ketones is reported in an extension of the Wadsworth-Emmons-Horner modification of the Wittig reaction. ... 

The Wittig reaction along with its modification (Horner-Emmons-Wadsworth) has been employed to generate a variety of interesting structures. For example, conjugated polyenals have been synthesized as shown in nation (46) <88SC51>. 

The Horner-Emmons-Wadsworth Modification of the Wittig Reaction (Section 16.6)... 

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