Horner reaction

Important and widely used variants of the Wittig reaction are based on carbanionic organophosphorus reagents, and are known as the Wadsworth-Emmons reaction, Wittig-Horner reaction or Horner-Wadsworth-Emmons reaction. As first reported by Horner, carbanionic phosphine oxides can be used today carbanions from alkyl phosphonates 13 are most often used. The latter are easily prepared by application of the Arbuzov reaction. The reactive carbanionic species—e.g. 14 —is generated by treatment of the appropriate phosphonate with base, e.g. with sodium hydride ... 

Wittig-Horner reaction, ° has several advantages over the use of phosphoranes. These ylids are more reactive than the corresponding phosphoranes, and when R is... 

Horner reactions of phosphonium ylide and phosphine oxide... 

A Michaelis-Arbusov rearrangement followed by a Wittig-Horner reaction is involved in preparation of the distyrylbenzene derivative 11.37, as shown in Scheme 11.15. Precautions must be taken in the first stage to minimise formation of the carcinogenic by-product bis(chloromethyl) ether 11.16. The stilbene bis-ester 11.38 can be made by a similar procedure, or alternatively by the reaction of ethyl acrylate with 4,4 -dibromostilbene in the presence of a palladium-based catalyst (Scheme 11.16), a synthesis that yields the required trans form of the brightener. 

When one of the reacting partners in the Wittig-Horner reaction, either the phosphine oxide or the carbonyl compound, has a double bond, the product is a diene. The Wittig-Horner reaction was utilized by Smith and coworkers in the total synthesis of milbemycin (equation 98)170. They found that when sodium hexamethyldisilazide was employed as a base, the desired E-diene selectivity is high (85%). Some examples from the literature where the Wittig-Horner reaction has been utilized for the construction of E-double bonds present in dienes and polyenes are given in Table 19171. 

TABLE 19. Dienes and polyenes through the Wittig-Horner reaction... 

In the case of the synthesis of 10,19,19,19-2H4-vitamin A, the most useful for biological studies, three deuterium atoms were incorporated into /i-ionone 30, in >98% by deuterium exchange with excess D2O in the presence of Na02H (and pyridine). The tri-deuteriated 30, utilized in Wittig-Horner reaction with dideuterio triethyl phosphonate, provided tetradeuteriated ethyl /J-ionilidene acetate 31 with more than 98% 2H4 (by NMR). No deuterium loss in the subsequent synthetic steps was observed as evidenced by MS and NMR analysis. 

Isoe, S., Katsumra, S., and Kimura, A., Total synthesis of ( )-jolkinolide A, B, and E utilizing a new mild esterification followed by intramolecular Wit-tig-Horner reaction, Tetrahedron, 45, 1337, 1989. 

Vinyl phosphonates have been used in the construction of valerenic acid terpenoids 169 (Scheme 42).101 Both five-and six-membered rings can be formed via the vinyl phosphonate Alder-ene reaction which can be catalyzed by a variety of Lewis acids. The resulting structures 167 are suitable for Wittig-Horner reaction to give diene 168. Subsequent reactions access valerenic acid terpenoids 169. The chirality of the carbon bearing the phosphonate and ester is transferred, but is subsequently lost in the Wittig-Horner step. 

The diphenylamino-substituted PPV107, with solubilizing alkoxy groups, was synthesized by Shi and Zheng [150] via Wittig-Horner reaction (Chart 2.23). Its PL (555 nm) is very similar to that of diamino-PPV 64 and dialkoxy-PPV 14 homopolymers. The PLQY is rather high in solution (80%), but it drops to only 8% in films. Consequently, only a moderate EL efficiency of 0.6cd/A was obtained with this material (device ITO/PEDOT/107/Mg/Al) [150]. Almost simultaneously, Kido and coworkers [151] reported a similar diphenylamino-substituted PPV copolymer 108, which affords very efficient PLEDs. The device ITO/PEDOT/108/Ca/Al... 

The anomeric appendage of imino sugars has been exploited to generate mimics of glycoconjugates. An example is reported in Fig. 42 for the synthesis of nojirimycinyl C-(L)-serine 109,73 in which the ozonolysis of the allylic appendage generates the aldehydes 106, on which the aminoacidic moiety was inserted by Wittig-Horner reaction. 

When methylene bisphosphonate (169) is reacted in a Horner reaction with an aromatic aldehyde, the alkenyl phosphonate 170 is produced (Scheme 5.25). By metalation with LDA in THF, this is converted to the vinyllithium intermediate 171 that, with the ketone 172, affords a Baylis-Hillman reaction-type product, 173 on base treatment, this is converted to the arylallene 174 [67]. 

Only low yields (10%) of coumarin were obtained by the intramolecular Wittig-Horner reaction of 2-(diethoxyphos-phorylacetoxy)benzaldehyde using (35) as an EGB (formed ex situ in MeCN) [98]. 

Data Characterizing the Wittig—Horner Reaction between Furfural and Triethyl Phosphonoacetate in the Presence of Basic Catalysts in a Batch Reactor (294)... 

An investigation of the Wittig-Horner reaction taking place under sonochemical irradiation and catalyzed by the activated Ba(OH)2 showed that the process could be markedly improved. The sonochemical process increased the reaction rate over... 

Nucleophilic Addition to Carbonyl Compounds and -Unsaturated Carbonyl Compounds.—Although the reactions of 17-oxo-steroids with various carbanion reagents are reported to have varying success/ the use of alcohols or DMF as solvents appears to facilitate the Wittig-Horner reaction/ For example, the ketone (97) was converted with (Et0)2P0CHC02Et into the E-ethyl ester (98) in... 

Wittig-Horner reaction (see p. 241). Photolysis of the nitrite of the 21-chloro-20-hydroxy-compound (194) gave the 18-oximino-compound (195) which on Jones oxidation was converted into the chlorolactone (196). Hypoiodite reaction of the 21-chloro-20-hydroxy-compound (194) also gives the chloro-lactone (196) which with modification gives 18-hydroxy-11-deoxycorticosterone (see also ref. 198). 

Preparation of 18,18,18-trifluororetinal required synthesis of trifluorocyclocitral as precursor. For this purpose, the 1,4-addition of a cuprate (prepared from an a>-bromo-trifluoromethylcarbinol) onto a vinylidene phosphonate was performed. The alcohol moiety is then deprotected and oxidized into ketone. A further intramolecular Wittig-Horner reaction, followed by reduction, led to trifluorocyclocitral. 18,18,18-Trifluororetinal is then easily obtained from this compound (Figure 4.25). ... 

Some syntheses of 2- or 3-fluoro-2,3-dideoxyfuranoses have been described starting from l- or D-glyceraldehyde or from other acyclic precursors. They involve a Wittig-Horner reaction, followed by a Sharpless epoxidation (Figure... 

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