Horner Wadsworth-Emmons HWE reaction

Scheme 8 summarizes the introduction of the missing carbon atoms and the diastereoselective epoxidation of the C /C double bond using a Sharpless asymmetric epoxidation (SAE) of the allylic alcohol 64. The primary alcohol 62 was converted into the aldehyde 63 which served as the starting material for a Horner-Wadsworth-Emmons (HWE) reaction to afford an E-configured tri-substituted double bond. The next steps introduced the sulfone moiety via a Mukaiyama redox condensation and a subsequent sulfide to sulfone oxidation. The sequence toward the allylic alcohol 64 was com-... 

The asymmetric Horner-Wadsworth-Emmons (HWE) reaction of l,3-dioxan-5-ones with phosphonate 184 and a chiral diamine was reported. With the /i r/-butyl-substituted l,3-dioxan-5-one, the product possesses a chiral axis. It was obtained in good yield and with 80% ee (Scheme 53) <2002TL281>. The HWE reaction with similar heterocyclic substrates was used to provide conformationally restricted arachidonic acid derivatives <1999TA139>. 

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

In the Horner-Wadsworth-Emmons (HWE) reaction, a lithium, sodium or potassium salt of a P-keto-phosphoric acid dialkyl ester or an a-(alcoxycarbonyl) phosphoric acid dialkyl ester is reacted with an aldehyde to form an a,p-unsaturated ketone or an a,p-unsaturated ester as product and a phosphoric acid dialkyl ester as byproduct. The product of a Horner-Wadsworth-Emmons reaction possesses a new -configured C=C double bond. To obtain products with Z-confi-guration of the C=C double bond the Still-Gennari variant or the Ando variant can be employed. The Still-Gennari variant uses two partly fluorinated F3C-CH2-O groups at the phosphorus and the Ando variant uses two aryloxy residues and the transferable alcoxycarbonyl group at the phosphorus. 

Kokin, K., litake, K.-l., Takaguchi, Y., Aoyama, H., Hayashi, S., Motoyoshiya, J. A study on the Z-selective Horner-Wadsworth-Emmons (HWE) reaction of methyl diarylphosphonoacetates. Phosphorus, Sulfur Silicon Reiat. Elem. 1998,133, 21-40. 

Barium hydroxide [33, 34] is a strong base which has been employed not only in organic synthesis but also for other purposes. The commercially available octahydrate, l a(OI 1)2 8 11,/) is often used after transformation to the anhydrous form at 200-500 °C. Dehydrated Ba(OH)2 activated at 200°C is denoted C-200. It is known to be a heterogeneous basic catalyst in the Horner-Wadsworth-Emmons (HWE) reaction of triethyl phosphonoacetate (69) with aldehydes 70 to give the 3-substituted ethyl acrylates 71 (Scheme 5.13) [35]. The HWE reaction proceeds at 70 °C in 1,4-dioxane with a small amount of water. The yields of products 71 are usually better than those provided by typical basic catalysts such as NaOH or... 

Under high-pressure (0.8 GPa) the alkenylation of carbonyl compounds 196 with phosphonate 197 [Horner-Wadsworth-Emmons (HWE) reaction] is accomplished efficiently (50-90% yields) at room temperature in the presence of triethylamine without further activation by Lewis acid. In contrast, reactions carried out at atmospheric pressure give negligible yields (0—8%) (Scheme 7.50). 

The Horner-Wadsworth-Emmons (HWE) reaction involves the addition of a stabilized phosphonate anion to an aldehyde or ketone to afford an intermediate which undergoes an elimination reaction to form predominately the ( )-alkene. The HWE reaction has been applied inter- and intramolecularly to simple as well as highly functionalized systems. 

The combination of pressure and catalysis can also be used to design a new domino process. The alkenylation of aldehydes with phosphonates (Horner-Wadsworth-Emmons (HWE) reaction) is readily accomplished at room temperature under pressure in the presence of triethylamine as a base. These mild con-... 

TMG (1) is used as a base in Horner-Wadsworth-Emmons (HWE) reactions [81]. For example, the sequential reaction of 1,3-diformylbenzene with different phosphorylglycines... 

The Horner-Wadsworth-Emmons (HWE) reaction of a carbonyl compound with an a-lithiated phosphonate is an extremely useful method for introducing a double bond. In order to create a chiral compound having a double bond, 4-substituted cyclohexanones, 3-substituted cyclohexanones, 2,2-disubstituted cyclohexane-l,3-diones, or ketenes would be potential carbonyl substrates for the enantioselective HWE reaction, as Rein and coworker proposed [Fig. (15)] [69]. Only 4-substituted cyclohexanones have so far been applied to the enantioselective HWE reaction. 

Phosphonates are useful nucleophiles in the Michael addition. The presence of the phosphonate group enables subsequent Horner-Wadsworth-Emmons (HWE) reaction. In this way, initial Michael adducts were transformed into biologically relevant 8-lactams and 5-lactones (Scheme 8.12). Transformation involved reduction of the aldehyde moiety, cyclisation and Horner-Wadsworth-Emmons (HWE) reaction with formaldehyde. 

Aral and Shioiri reported the first example of a catalytic asymmetric Horner-Wadsworth-Emmons (HWE) reaction promoted by chiral PTC catalyst 7a, which gives optically active a,(3-unsaturated esters 107 (57% enantiomeric excess). Although the enantioselectivity was not satisfactory, the results suggested a significant possibility that PTC catalysis can mediate various asymmetric conversions (Scheme 16.39). ... 

Finally, Ranoux et al. have prepared and evaluated C-glycosyl compounds as hydrotropes." " They are advantageously more stable towards acid and en matic hydrolysis than their O-glycoside counterparts, which may decrease their biodegradability in return. The Horner-Wadsworth-Emmons (HWE) reaction was used to prepare various C-glycosyl... 

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