Olefins Horner-Wadsworth-Emmons reaction

We have already seen the bishydroxylation using 0s04 and NMO this time lead tetraacetate is used to cleave the diol and yield the aldehyde. The phosphorane (Me0)2P(0)CHN2 is named the Gilbert-Seyferth reagent. 8 It basically behaves like the phosphoranes in the Horner-Wadsworth-Emmons reaction described above, except that the olefin subsequently loses nitrogen, creating the desired triple bond (also see Chapter 10). 

The protected methyl glycoside 3 is converted to the corresponding aldehyde by Swern oxidation using oxalyl chloride activated DMSO. Further reaction with triethyl phosphonoacetate and sodium hydride -known as the Horner-Wadsworth-Emmons reaction - provides selectively the trans et /Tun saturated ester 4 in 72 % yield. This valuable alternative to the Wittig olefination protocol uses phosphonate esters as substrates which are readily available from alkyl halides and trialkyl phosphites via the Arbuzov rearrangement.9 co2Et Reaction of the phosphonate with a suitable base gives the... 

Horner-Wadsworth-Emmons reactions are C—C-forming condensation reactions between the Li, Na, or K salt of a /J-keto- or an -(alkoxycarbonyl)phosphonic acid dialkyl ester and a carbonyl compound (cf. Figure 4.41). These reactions furnish a,f)-unsaturated ketones or a j8-unsaturated esters, respectively, as the desired products and a phosphoric acid diester anion as a water-soluble by-product. In general, starting from aldehydes, the desired compounds are produced fraus-selectively or in the case of olefins with trisubstituted C—C double bonds -selectively. 

The stereostructure of the alkoxide intermediate of a Horner-Wadsworth-Emmons reaction which finally leads to the trans-o cim was recorded in Figure 9.14 (as formula A). The Still-Gennari variant of this reaction (Figure 9.15) must proceed via an alkoxide with the inverse stereostructure because an olefin with the opposite configuration is produced. According to Figure 9.16, this alkoxide is a 50 50 mixture of the enantiomers C and ent-C. Each of these enantiomers contributes equally to the formation of the finally obtained cw-configured acrylic ester D. 

All the carbons of the target were introduced by a Horner-Wadsworth-Emmons reaction of ent-427 with a-ethylacrolein, which gave a mixture of ( ) and (Z) olefins 437. The synthesis of the E) isomer of 437 constitutes a formal synthesis of coronafacic acid because its conversion to the natural product has been reported by Nara, Toshima, and Ichihara [90]. They reported that 437-E could be cyclized with base to hydrindenones 438 and 439 in 71 % yield. After purification, the major diastereomer 438 could be hydrolyzed to coronafacic acid in 95 % yield. 

Related reactions Horner-Wadsworth-Emmons olefination, Horner-Wadsworth-Emmons olefination - Still-Gennari modification,... 

Related reactions Homer-Wadsworth-Emmons olefination, Horner-Wadsworth-Emmons olefination - Still-Gennari modification, Julia-Lithgoe olefination, Peterson olefination, Takai-Utimoto olefination, Tebbe olefination, Wittig reaction - Schlosser modification ... 

The unstable silyl ether in 232 was replaced by a more stable acetoxy ketone 233 which was not isolated. A Horner-Wadsworth-Emmons reaction was used for the Wittig-style olefination (chapter 15). A nitrile 234 replaced the carbonyl group in 230 as it was found easier to reduce nitriles in conjugative fashion. 

The starting material for this synthesis was iV,Ar-dibenzyl phenylalanal (1118), which is readily accessible from the corresponding amino acid (743). This was submitted to a Horner-Wadsworth-Emmons reaction with diethyl 3-oxo-2-butylphosphonate. The olefin obtained was then mono-iV-debenzylated, and then treated with t-butyldimethylsUyl triflate and 2,6-lutidine to give the sUyl enol ether 1119. Addition-elimination by treatment with methylene lactone 1120, synthesized earlier (744), provided Diels-Alder substrate 1121, which at high temperature... 

Closely related to the Wittig reaction is the Horner-Wadsworth-Emmons reaction, where a stabilized phosphonate carbanion reacts with an aldehyde or ketone to yield an olefin. 

The Horner-Wadsworth-Emmons Reaction and Related Olefinations... 

The use of the Horner-Wadsworth-Emmons reaction for stereocontrolled olefin syn- thesis in the field of natural products has been reviewed in 2000-2013. ( )... 

Recent advances in the stereoselective olefination of phosphorus-stabilized carbon nucleophiles have been reviewed. Recent applications of the Horner-Wadsworth-Emmons reaction to the synthesis of natural products have been highlighted. ... 

Recent advances in the stereoselective olefination of phosphorus-stabilized carbon nucleophiles have been reviewed. Applications of the Horner-Wadsworth-Emmons reaction to the synthesis of natural products have been highligted. A highly Z-selective synthesis of a, -unsaturated nitriles using the Homer-Wadsworth-Emmons reaction has been reported this involves a new nitrile reagent, (o-t-BuC6H40)2P(0)CH2CN, which reacts with various types of aldehydes with 86 to >99% Z selectivity. 

Formation of C-N bond has raised of interest in the scientific community in the last 10 years. In this context, the formation of enamides is a valuable protocol. In addition to conventional approaches that include condensation of amides and aldehydes, addition of amides to alkynes, acylation of imines, Curtius rearrangement of a,jS-unsaturated acyl azides, amide Peterson olefination, and Wittig and Horner-Wadsworth-Emmons reactions, several transition metal-catalyzed methods have been developed that allow the synthesis of enamides.Inspired by the analogous arylation of amines catalyzed by palladium or copper complexes (Buchwald-Hartwig reaction), a new approach for the synthesis of enamides has been published recently, which allows to prepare enamides from readily available starting materials (amides and vinyl halides) proceeding under very mild conditions. Thus, we decided to test the Porco-Buchwald amidation of vinyl halides in our synthesis [144-146]. 

Propose a mechanism for the Horner-Wadsworth-Emmons reaction. The reaction of aldehydes with 10 provides 1,2-disubstituted olefins with high E-selectivity. Provide (or look up) a rationale for this observation. Then explain why the reaction of 3 with 10 shows little stereoselectivity. (CJH-2)... 

Horner-Wadsworth-Emmons reaction of 153 with diethyl cyanomethylphosphonate in the presence of t-BuOK at —78°C to 0°C underwent olefination/isomerization/Claisen rearrangement cascade to give an enantiomerically enriched oxindole (—)-154 in 89% yield and 99% ee (Scheme 21.35). 

Aziridine-2-phosphonates spiro-fused with 2-oxindole (790) have been prepared by a straightforward Horner-Wadsworth-Emmons reaction of ethyl 7V- [(4-nitrophenyl)sulfonyl]oxy -carbamate (791) and 3-(phosphoryl-methylene)oxindoles (792) in the presence of calcium oxide. Oxindoles (792) were also transformed into novel oxirane-2-phosphonates (793), as oxygen analogues of (790), by reaction with H202/Na0H (Scheme 201). " Cinchonine-based thiourea (797) catalysed asymmetric Michael addition of simple p-oxo-alkyl phosphonates (794) to nitro olefins (795), which afforded valuable a-substituted p-oxo phosphonates (796) in satisfactory yields with good to excellent enantioselectivities (up to 98% ee) (Scheme 202). ... 

HORNER - WADSWORTH - EMMONS Olelination Wittig type reaction of ptwsptionale stabilized carbanions with aldehydes or ketones to form olefins... 

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