Horner-Emmons-Wadsworth modification

The Horner-Emmons-Wadsworth Modification of the Wittig Reaction (Section 16.6)... [Pg.683]

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>. [Pg.571]

The preparation of a,/ -unsaturated aldehydes and ketones is exemplified by the following four important methods (a) the oxidation of the corresponding unsaturated primary or secondary alcohol (b) the Horner-Emmons or Wadsworth-Emmons modification of the Wittig reaction248 (c) the aldol con-... [Pg.798]

THE HORNER-EMMONS OR WADSWORTH-EMMONS MODIFICATION OF THE WITTIG REACTION... [Pg.799]

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. [Pg.80]

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. [Pg.21]

Horner-Wadsworth-Emmons (HWE) reaction There is a close relationship between the original Wittig alkenation and its phosphonate ester modification which is known as... [Pg.161]

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. ... [Pg.626]

HORNER-WADSWORTH-EMMONS OLEFINATION - STILL-GENNARI MODIFICATION... [Pg.214]

Horner-Wadsworth-Emmons Olefination (Still-Gennari modification) 214... [Pg.507]

Related reactions , Horner-Wadsworth-Emmons olefination - Still-Gennari modification, Julia-Lithgoe olefination, Peterson... [Pg.603]

Horner-Wadsworth-Emmons Oiefination - Still-Gennari Modification.214... [Pg.604]

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 ... [Pg.650]

Related reactions Horner-Wadsworth-Emmons olefination, Horner-Wadsworth-Emmons oiefination - Stiii-Gennari modification,... [Pg.708]

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. [Pg.157]

Ando Modification of the Horner-Wadsworth-Emmons Reaction... [Pg.174]

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... [Pg.316]

Other references related to the Horner-Wadsworth-Emmons oleflnation and to the Still-Gennari modification are cited in the corresponding literature. [Pg.1487]

Purpose To demonstrate the synthesis of a stilbene by the Horner-Wadsworth-Emmons modification of the Wittig reaction. [Pg.610]

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. [Pg.298]

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... [Pg.298]

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