Wittig reaction, Horner-Emmons modification

Poly(p-arylene vinylene)s were synthesized with low molecular weight via the Horner-Emmons modification of the Wittig reaction [12] and via the precursor route [13]. Efforts to synthesize poly(p-anthrylene vinylene) via a Heck reaction failed [15]. We chose ROMP followed by a dehydrogenation step to produce poly(2-alkyl-9,10-anthrylene vinylene) as has been shown before for poly(l,4-naphthylene vinylene) by Pu et al. [16]. The initiator used was the Schrock molybdenum carbene shown in Figure 1 and our goal was to produce a soluble poly(anthrylenevinylene). 

A one-carbon homologation of aldehydes and ketones to carboxylic acids has been reported to involve the Horner-Emmons modification of the Wittig reaction using diethyl-/er/-butoxy(cyano)-methylphosphonate (EtO)2 P0CH(CN)0/-Bu to produce ethyl-/pr/-butoxyacrylonitriles. The /er/-butyl ether group is cleaved by zinc chloride in refluxing acetic anhydride, and the a-acetoxyacrylonitrile is converted to the acid by solvolysis. 

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

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 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. ... 

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 ... 

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. 

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... 

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>. 

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. 

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

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. ... 

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. 

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

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