Wittig-Homer-Emmons-Wadsworth olefination

The Witting reaction has been investigated in aqueous conditions.305 Wittig olefination reactions with stabilized ylides (known as the Wittig-Homer or Homer-Wadsworth-Emmons reaction) are sometimes performed in an organic/water biphase system.306 Very often, a phase-transfer catalyst is used. Recently, the use of water alone as solvent... 

The results of the olefination reactions obtained with the Reformatsky approach are similar to those of the Wittig-Homer and the Homer-Wadsworth-Emmons methodologies. But in contrast to these, the position of the newly formed double bond in the Reformatsky approach is not always certain, as exemplified in the synthesis of the kappa opiate agonist [ C]PD-17,30212461. where a mixture of double bond isomers 242 and 243 was obtained. In this case, fortunately, the lack of selectivity was unimportant because both were... 

An important modification to the Wittig reaction is the use of stabilized phosphonate carbanions in olefin synthesis. This reaction, originally discovered by Homer but developed by Wadsworth and Emmons, is used extensively for transformation of a carbonyl... 

The formation of allenes by Wittig or Homer-Wadsworth-Emmons-olefination of ketenes is well established [1] for more recent examples, see (a) T. Minami,... 

Pommer et al.146) reported a synthesis of a stereoisomer mixture of JH1 using a Homer-Wadsworth-Emmons olefmation for introducing the double bond at C-2 of 184146). Three Wittig olefinations were applied in the condensation of C4 + C6 + + C5 + C2 synthons 147). The isomers obtained were separated by distillation (Scheme 35). 

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 ... 

Among the different methods for the synthesis of alkenes, none matches the versatility of carbonyl olefination.290 It has been extensively studied since the discovery of the Wittig reaction,291292 and a wide variety of approaches to transform carbonyl compounds into alkenes have been developed. Besides the classical Julia reaction,94 the most generally applicable methods for direct olefination of carbonyl compounds include the Wittig,291,293,294 Homer-Wittig,295,293,296 Homer-Wadsworth-Emmons,297,298,293 Peterson,299 301 Johnson,302 and Julia-Kocienski303,304 reactions. All of these methods involve the addition of a... 

The Homer-Wadsworth-Emmons reaction is also a useful option for producing olefins in the solid phase. Supported stabilized phosphonoactates, as they are more acidic than phosphonium salts, can readily give the corresponding ylides with weak bases such as DBU, DIPEA, EtaN. One still has to make sure that these reaction conditions are chemoselective. Both types of reactions, Wittig and Homer-Wadsworth-Emmons, have been successfully used in cyclative and/or functionalizing cleavage. 

The disadvantages of the Wittig reaction described in Section A led to the development of modified olefination methods based on phosphoryl-stabilized carbanions. The most important modification of the Wittig reaction in the field of carotenoid synthesis is olefination by means of phosphonate carbanions, as introduced by Homer [55] and by Wadsworth and Emmons [56]. 

The temporary presence of a carbon-carbon double bond can be advantageous for creating branches in a molecular skeleton by bond formation. This functionality can be obtained not only by olefin metathesis, but also by any carbonyl olefination reaction (Wittig [24], Homer-Wadsworth-Emmons [25], Peterson, or Julia-Lythgoe [9]) (Scheme 3.14). 

---