Sep 15, 2010 the extension of this reaction by the application of a phosphine oxide carbanion, instead of a phosphonium ylide is known as the horner reaction or wittig horner reaction, while the preparation of olefin from a phosphonate carbanion is commonly referred to as the hornerwadsworthemmons olefination. This reaction works by an initial basecatalyzed deacylation of the diazophosphonate, followed by fritschbuttenbergwiechell rearrangement of the vinylidene. Formally, the pwh reaction is the phosphorus analogue to the hornerwadsworthemmons reaction hwe, which allows. This reaction is named after its discoverer, the german chemist georg wittig. Dec 17, 2019 the key difference between wittig and wittig horner reaction is that wittig reaction uses phosphonium ylides, whereas wittig horner reaction uses phosphonatestabilized carbanions. Wittig and wittighorner reactions under phase transfer catalysis. Leopold horner 1911 2005 born in kehl am rhein germany. Wittighorner reaction hornerwadsworthemmons reaction. If r is an electron withdrawing group, then the ylide is stabilized and is not as reactive as when r is alkyl. The reaction of stabilized phosphonium ylides with aldehydes favors ealkene products. In this method, ethyl diethoxyphosphinylacetate and dimethylaminoacetaldehyde diethylacetal, replacing e4dimethylaminobut2enoyl acid hydrochloride and oxalyl chloride, were used to synthesize the. The reaction of aldehydes or ketones with stabilized phosphorus ylides phosphonate. Wittig reaction the wittig reaction is the reaction of an aldehyde or ketone with a triphenyl phosphonium ylide to give an alkene and triphenylphosphine oxide.
The hornerwadsworthemmons hwe version of the wittig reaction focuses on the use of more stabilized phosphonate ylides 203. The reaction is easy to carry out and proceeds under mild conditions. This solid is more effective catalyst than potassium carbonate or activated barium hydroxide catalyst c. This video gives mechanism of wittig reaction with stereochemistry and a lot of examples for csir net exam. Synthesis of stilbene by the wittig and horner wadsworthemmons reactions. Wittig and wittighorner reactions under phase transfer catalysis conditions. We will discuss the mechanism in greater detail in chapter 23, when we discuss the chemistry of hydrogens that are. Phosphonatestabilized carbanions are more nucleophilic and more basic than the corresponding phosphonium ylides. The wittig reaction was named after george wittig who converted carbonyl groups, such as aldehydes and ketones, into alkenes. Cesium carbonate is described as an efficient catalyst for the wittig. Wittig reaction major reference works wiley online library.
Likewise, phosphonatestabilized carbanions can be alkylated. Wittig reaction is an organic chemical reaction wherein an aldehyde or a ketone is reacted with a wittig reagent a triphenyl phosphonium ylide to yield an alkene along with triphenylphosphine oxide. Thus, the aroyl cyanides 220 were applied in reactions with 1,3dithiole wittig reagents 218 and hornerwittig reagent 219 to afford alkenes 221 possessing a. A comparison of wittig and wittig horner wadsworth emmons. Wittig reaction mechanism with reagent preparation detailed. In this study, it was used for the synthesis of the anticancer drug neratinib.
Wittig reagent stable wittig reagents where r3 is capable of stabilizing the negative charge from the carbanion through resonance ex. This reaction is more superior to wittig reaction since the carbanion generated from phosponates is more nucleophilic and the phosphate byproducts are water soluble and can be. You will generate an enolate anion stabilized by a phosphonium group a wittig reagent from the. The wittig reaction is an organic reaction used to convert a primary or secondary alkyl halide and an aldehyde or ketone to an olefin using triphenylphosphine and base. Mar 18, 2014 its time for the wittig reaction mechanism to be made easy. Wittig reaction and wittig horner reactions are important synthesis reactions in organic chemistry, which produce alkenes from aldehydes or ketones. Wittig and wittig horner reactions under phase transfer catalysis conditions article pdf available in central european journal of chemistry 14. The reaction mechanism is similar to the mechanism of the wittig reaction. Horner emmonswitting reaction in this experiment, a modified wittig reaction will be carried out to synthesize an alkene product. Wittig reactions, wittighorner reactions, phase transfer catalysis.
A typical wittig reaction starts by generating a wittig reagent, known as an ylide from an alkyl halide and triphenylphosphene. The phospha wittig horner reaction proceeds through stepwise pp cleavage of an oxadiphosphetane intermediate, followed by a 2,3sigmatropic rearrangement that paves. While many other routes to alkenes can proceed via elimination reactions e1 or e2. It uses a carbonyl compound as an electrophile, which is attacked by a phosphorus ylide the wittig reagent. Phosphawittighorner reagents with unsaturated substituents at iiip 10d,e can be prepared in analogous procedures. The alkene product 4 that you make today is the one that was used a few weeks ago as the colorizer for the chemiluminscence experiment it gave the green solution. The reaction between a phosphorane and an aldehyde or a ketone to form a phosphine oxide and an alkene is known as the wittig reaction fig. Solventfree method for making olefinic amino esters 205 from an aldehyde compound and a phosphonate derivative of glycine was established by lamaty scheme 2. The phosphawittighorner pwh reaction, as first coined by mathey and coworkers. Mechanism of the phosphawittighorner reaction ncbi.
Sep 17, 2019 this video gives mechanism of wittig reaction with stereochemistry and a lot of examples for csir net exam. Industrial applications of the wittig reaction springerlink. The wittig reaction was discovered in 1954 by georg wittig and desc ribed in his pioneering publication titled uber triphenylphosphinmethylene als ole. The wittig reaction allows the preparation of an alkene by the reaction of an aldehyde or ketone with the ylide generated from a phosphonium salt. I also provide some useful tips that you guys should try to. Preparation of allenes with a chiral phosphine oxide wittig horner reaction tanaka, otsubo, fuji tetrahedron lett.
The mechanism of the hwe reaction resembles that of the wittig reaction. If a potassium base was used to generate the phosphine oxide anion, the reaction with a carbonyl compound proceeded as in the wittig. Revisiting the phosphawittighorner reaction organometallics. These reagents are more nucleophilic than phosphonium ylides, though of course this means that they are less basic.
Its time for the wittig reaction mechanism to be made easy. The hornerwadsworthemmons hwe reaction is a chemical reaction used in organic. The geometry of the resulting alkene depends on the reactivity of the ylide. Despite of the synthetic versatility of the pwh reaction, it has been a greatly underexplored method for the preparation of phosphaalkenes. Wittig and wittighorner reactions under phase transfer catalysis conditions article pdf available in central european journal of chemistry 14. In 1958, horner disclosed a modified wittig reaction employing phosphonatestabilized. This is modified wittig reaction in which carbanions generated from phosphonate esters are used instead of phosphonium ylides. Jill jaworske organic chemistry ii lab november 4th, 2019 lab. A comparison of wittig and wittig horner wadsworth emmons reagents in reactions with some. Pdf wittig and wittighorner reactions under phase transfer. A variation of the wittig reaction, called the hornerwadsworthemmons hwe reaction gives e alkenes. Sep 28, 2012 the wittighorner reaction is a classic method to get alkenes by reaction phosphonates with carbonyl compounds. Phosphorus, sulfur, and silicon and the related elements. In 1958, leopold horner published a modified wittig reaction using phosphonatestabilized carbanions.
The wittighorner reaction for the synthesis of neratinib. View lab report lab report 7 wittig and horner wadsworthemmons reactions. This variant of the wittig reaction is valuable because. Samantha adkison chem 2122 l1 experiment 1 061617 joshua albus 1 out of abstract. The most important use of ylides in synthesis comes from their reactions with aldehydes and ketones, which are initiated in every case by a covalent bonding of the nucleophilic alphacarbon to the electrophilic carbonyl carbon. The wittig reaction was discovered in 1954 by georg wittig, for which he was awarded the nobel prize in chemistry in 1979. This is followed by a presentation of the current state of the art regarding phosphinecatalyzed wittig reactions. It should not be confused with the wittig rearrangement. The first section summarizes how arsenic and telluriumbased catalytic wittig type reaction systems were developed first due to the relatively easy reduction of the oxides involved. A list of common conditions for the wittig reaction. Synthesis of stilbene by the wittig and hornerwadsworth. In contrast to phosphonium ylides used in the wittig reaction, phosphonatestabilized carbanions are more nucleophilic but less basic. Wittig reaction with stereochemistry organic name reactions.
Synthesis of alkenes intro the wittig reaction is one of the premier methods for the synthesis of alkenes. This type of carboncarbon bondforming reaction led him to the nobel prize in 1979. The wittig reaction or wittig olefination is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide often called a wittig reagent to give an alkene and triphenylphosphine oxide. The stereochemistry is set by steric approach control, where the antiperiplanar approach of the carbanion to the carbon of the carbonyl group is favored when the smaller aldehydic hydrogen eclipses the bulky phosphoranyl moiety. Mechanism the general mechanism of the wittig reaction is shown above. Wittig reactions are more general in that the product carbonyl does not need to have an attached carbonyl. Lab report 7wittig and hornerwadsworthemmons reactions. If a potassium base was used to generate the phosphine oxide anion, the reaction with a carbonyl compound proceeded as in. Emmons further defined the reaction in contrast to phosphonium ylides used in the wittig reaction, phosphonatestabilized carbanions are more nucleophilic but less basic.
Jun 17, 20 the phosphawittighorner reaction top, for which the mechanism is unknown, and the carbonanalogue hornerwadsworthemmons reaction bottom. Follow me in my walkthrough video and we can do the mechanism together. Pdf wittig and wittighorner reactions are favorite tools in preparative organic chemistry. For the wittig reaction follow the procedure in the book. Organic chemistry portal, wittighornerreaction rsc ontology id, rxno. This study revealed that the hwe reaction of the lithium enolate derived from trimethyl phosphonoacetate with acetaldehyde occurs with the addition of the lithium enolate to aldehyde, followed by oxaphosphetane formation, pseudorotation, p. This reaction substitutes phosphonatestabilized carbanions for the phosphonium ylides used in the standard wittig reaction. The wittig reaction chem 115 fan liu stabilized ylides are proposed to have a later and more productlike transition state with 1e thermodynamically favored over 1z. Co2r are much more stable often commercially available. The phosphawittighorner reaction proceeds through stepwise pp cleavage of an oxadiphosphetane intermediate. The mechanism beings with attack of the pph 3 on the alkyl halide which releases the halide anion and forms a phosphonium ion. Wittig and wittighorner reactions under phase transfer. It is widely used in organic synthesis for the preparation of alkenes.
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