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The Diels-Alder reaction
The Diels-Alder reaction

The Diels-Alder reaction is an organic chemical reaction (specifically, a cycloaddition) between a conjugated diene and a substituted alkene, commonly termed the dienophile, to form a substituted cyclohexene system. Organic reactions are Chemical reactions involving Organic compounds The basic Organic chemistry reaction types are Addition reactions Elimination A cycloaddition is a Pericyclic Chemical reaction, in which two π bonds are lost and two σ bonds are gained the resulting reaction is a Dienes or diolefins are Hydrocarbons which contain two double bonds. In Organic chemistry, an alkene, olefin, or olefine is an unsaturated Chemical compound containing at least one Carbon The Diels-Alder reaction is an Organic chemical reaction (specifically a Cycloaddition) between a conjugated Diene and a substituted Alkene, Cyclohexene is a colorless clear Liquid Cycloalkene with an intense aversive characteristic sharp smell reminiscent of an Oil refinery. [1][2][3] The reaction can proceed even if some of the atoms in the newly-formed ring are not carbon. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Some of the Diels-Alder reactions are reversible; the decomposition reaction of the cyclic system is then called the Retro-Diels-Alder. For example, Retro-Diels-Alder compounds are commonly observed when a Diels Alder product is analyzed via mass spectrometry. Mass spectrometry is an analytical technique that identifies the chemical composition of a compound or sample based on the Mass-to-charge ratio of charged particles

Otto Paul Hermann Diels and Kurt Alder first documented the novel reaction in 1928 for which they were awarded the Nobel Prize in Chemistry in 1950 for their work on the eponymous reaction. Otto Paul Hermann Diels (23 January 1876 &ndash 7 March 1954 was a German chemist. Kurt Alder (10 July 1902 &ndash 20 June 1958 was a German chemist and Nobel laureate. The Nobel Prize in Chemistry (Nobelpriset i kemi is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of Chemistry. Year 1950 ( MCML) was a Common year starting on Sunday (link will display the full calendar of the Gregorian calendar. .

The Diels-Alder reaction is generally considered the "Mona Lisa" of reactions in organic chemistry since it requires very little energy to create the very useful cyclohexene ring[4][5][6][7]. Cyclohexene is a colorless clear Liquid Cycloalkene with an intense aversive characteristic sharp smell reminiscent of an Oil refinery.

Contents

Reaction mechanism

The reaction occurs via a single transition state, which has a smaller volume than either the starting materials or the product. The transition state of a Chemical reaction is a particular configuration along the Reaction coordinate. It is an associative type of reaction, and it is sped up by very high pressures. Diels-Alder is an example of a pericyclic reaction. In Organic chemistry, a pericyclic reaction is a type of Organic reaction wherein the Transition state of the molecule has a cyclic geometry and the reaction

Some free-radical versions of this reaction have been observed, though these are not Diels-Alder reactions as the stereochemistry at the carbons is scrambled. In Chemistry, radicals (often referred to as free radicals) are atoms molecules or ions with Unpaired electrons on an otherwise Open shell Stereochemistry, a subdiscipline of Chemistry, involves the study of the relative spatial arrangement of Atoms within Molecules An important branch These are step-wise reactions of the free radicals which form the new bonds in at least two steps. An example of this type of reaction is the reaction of selenobenzophenone with a 1,3-diene (See: thioketones). Thioketones are Organic compounds related to conventional Ketones Instead of the formula R2C=O thioketones or thiones as they are also called have the

The diene

The diene component in the Diels-Alder reaction can be open-chain or cyclic and it can have many different kinds of substituents. Dienes or diolefins are Hydrocarbons which contain two double bonds. In Organic chemistry, a substituent is an atom or group of atoms substituted in place of a Hydrogen atom on the Parent chain of a Hydrocarbon [8] There is only one limitation: it must be able to exist in the s-cis conformation. Trans-2-butenesvg|right|thumb|Trans-2-butene]] In Chemistry, cis-trans isomerism or geometric isomerism or configuration isomerism is a form of Butadiene[9] itself normally prefers the s-trans conformation, with the two double bonds as far away from each other as possible. If there are substituents larger than hydrogen then steric hindrance may influence the relative stabilities of the conformations. See also Intramolecular forces ' Steric effects arise from the fact that each Atom within a Molecule occupies a certain For simple cases, the barrier to rotation about the central bond is small and rotation to the less favourable but reactive s-cis conformation is rapid. Cyclic dienes that are permanently in the s-cis conformation are exceptionally reactive in Diels-Alder reactions (cyclopentadiene is a classic example), while cyclic dienes that are permanently in the s-trans conformation and cannot adopt the s-cis conformation will not undergo the Diels-Alder reaction at all. Cyclopentadiene is a Chemical compound with the formula C5H6 This colorless liquid organic chemical has a strong An especially reactive diene is Danishefsky’s diene. Danishefsky’s diene (Kitahara diene is an Organic compound and a Diene with the formal name trans -1-methoxy-3-trimethylsilyloxy-13-butadiene named after

Dendralenes are a new class of experimental DA dienes. Dendralenes are discrete Acyclic cross-conjugated Polyenes The simplest dendralene is Butadiene (1 or dendralene followed by

Unstable dienes, such as o-quinodimethane, can be generated in situ. In situ (ɪn siːˈtuː is a Latin phrase meaning in the place. Aromatic stabilization in the product of a DA reaction using such a diene is, in some cases, the reason behind the very high reactivity and lack of stability of such diene. The use of such unstable dienes is advantageous, despite the trouble, in that the products will contain newly formed aromatic six-membered rings.

Benzenoid compounds rarely undergo DA reactions and often require very reactive dienophiles. One example of such rare reaction is the Wagner-Jauregg reaction. The Wagner-Jauregg reaction is a classic Organic reaction in Organic chemistry, named after Theodor Wagner-Jauregg, describing the Diels-Alder reaction

The dienophile

In a typical Diels-Alder reaction, the dienophile has an electron-withdrawing group conjugated to the alkene. The Polar effect or electronic effect in Chemistry is the effect exerted by a Substituent on modifying Electrostatic forces operating on a nearby Though common, this feature is not exclusive of Diels-Alder dienophiles. There must be some extra conjugation, at least a phenyl group or chlorine atom. In Organic chemistry, the phenyl group or phenyl ring (often abbreviated as -Ph) is the Functional group with the formula - Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and The dienophile can be activated by a Lewis acid such as niobium pentachloride. Niobium(V chloride, also known as niobium pentachloride, is a yellow crystalline solid often used as a starting material in Niobium chemistry [10]

Dienephile activation by Lewis acid

Cyclopentadiene does not react with cyclohexenone in ethyl acetate unless the Lewis acid is present. Cyclopentadiene is a Chemical compound with the formula C5H6 This colorless liquid organic chemical has a strong Cyclohexenone is an Organic compound which is a versatile intermediate used in the synthesis of a variety of chemical products such as pharmaceuticals and fragrances Ethyl acetate ( systematically, ethyl ethanoate commonly abbreviated EtOAc or EA is the Organic compound with the formula CH3COOCH2CH3 The yield improves when reaction temperature is lowered to -78°C because polymerization side reactions are prevented. In Polymer chemistry, polymerization is a process of reacting Monomer Molecules together in a Chemical reaction to form three-dimensional networks Niobium pentachloride catalysis gives only the endo conformer. Endo-exo isomerism is a special type of Isomerism found in Organic compounds with a Substituent on a bridged ring system The same reaction with aluminium chloride results in an endo and exo mixture. Aluminium chloride (AlCl3 is a compound of Aluminium and Chlorine. Many of these Lewis acids are not good catalysts for the reaction of α,β-unsaturated carbonyls, this is because the carbonyl oxygen binds too tightly to the metal centre. A far better catalyst for such a system is a combination of silver perchlorate and Lawesson's reagent in cold dichloromethane. Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen Perchlorates are the salts derived from Perchloric acid ( H[[chlorine Cl]] O4) Lawesson's reagent, or LR, is a Chemical compound used in Organic synthesis as a Thiation agent Dichloromethane ( DCM) or methylene chloride is the Chemical compound with the formula CH2Cl2

It is well known that it is possible to use heteroatom containing dienophiles for Diels-Alder reactions, for instance Lawesson's reagent (and diferrocenyl dithiadiphosphetane disulfide) can react with 1,3-dienes to form six membered ring adducts. Lawesson's reagent, or LR, is a Chemical compound used in Organic synthesis as a Thiation agent Also selenoketones and thioketones are able to react in the same way with 1,3-dienes. Thioketones are Organic compounds related to conventional Ketones Instead of the formula R2C=O thioketones or thiones as they are also called have the Imines are reactants in the Aza Diels-Alder reaction. An imine is a Functional group or Chemical compound containing a Carbon – Nitrogen Double bond. The Aza Diels-Alder reaction converts Imines and Dienes to Tetrahydropyridines This Organic reaction is a modification of the Diels-Alder

Dienophiles can be chosen to contain a "masked functionality". The dienophile undergoes Diels-Alder reaction with a diene introducing such a functionality onto the product molecule. A series of reactions then follow to transform the functionality into a desirable group. The end product cannot not be made in a single DA step because equivalent dienophile is either unreactive or inaccessible. An example of such approach is the use of α-chloroacrylonitrile (CH2=CClCN). When reacted with a diene, this dienophile will introduce alpha-chloronitrile functionality onto the product molecule. This is a "masked functionality" which can be then hydrolyzed to form a ketone. α-Chloroacrylonitrile dienophile is an equivalent of ketene dienophile (CH2=C=O), which would produce same product in one DA step. A ketene is an Organic compound of the form R2C=C=O Hermann Staudinger pioneered the research of ketenes The problem is that ketene itself cannot be used in Diels-Alder reactions because it reacts with dienes in unwanted manner (by [2+2] cycloaddition), and therefore "masked functionality" approach has to be used. A cycloaddition is a Pericyclic Chemical reaction, in which two π bonds are lost and two σ bonds are gained the resulting reaction is a [11]

Other such functionalities are phosphonium substituents (yielding exocyclic double bonds after Wittig reaction), various sulfoxide and sulfonyl functionalities (both are acetylene equivalents), and nitro groups (ketene equivalents). In chemistry the phosphonium Cation is a positively charged polyatomic ion with the chemical formula PH4+ resulting from Protonation of The Wittig reaction is a Chemical reaction of an Aldehyde or Ketone with a triphenyl phosphonium ylide (often called a Wittig reagent A sulfoxide is a Chemical compound containing a sulfinyl Functional group attached to two carbon atoms A sulfonyl group is an organic radical or Functional group obtained from a Sulfonic acid by the removal of the Hydroxyl group Acetylene ( IUPAC name ethyne), C2H2 is a Hydrocarbon belonging to the group of Alkynes It is the simplest of all alkynes

Heterodienophiles

No major loss in reactivity of dienophile is seen when one, or both, of the carbons are substituted for another variety of atom. [12] Carbonyl groups, for example, can successfully react with dienes to yield pyranoid rings. In Organic chemistry, a carbonyl group is a Functional group composed of a Carbon Atom double-bonded to an Oxygen In Chemistry, a pyran is a six membered Heterocyclic ring consisting of five Carbon atoms and one Oxygen atom and containing two Double Generally, the endo transition state is favored in this case. The transition state of a Chemical reaction is a particular configuration along the Reaction coordinate.

Nitroso compounds (N=O) react to form oxazine-like compounds (cyclic molecules with nitrogen and oxygen present in the six-membered ring). [13] Another group of dienophiles successfully used for DA reactions is imines. An imine is a Functional group or Chemical compound containing a Carbon – Nitrogen Double bond. [14] Such reactions are useful for preparation of alkaloid and other polycyclic compounds. This article is about the chemical compounds alkaloids For the Pharmaceutical company in the Republic of Macedonia see Alkaloid (company.

Stereoselectivity in DA Reactions

Diels-Alder reactions can lead to formation of a variety of structural isomers and stereoisomers (enantiomers and diastereomers). This article is about the chemical concept For "isomerism" of atomic nuclei see Nuclear isomer. Stereoisomers are isomeric molecules that have the same molecular formula and sequence of bonded atoms (constitution but which differ in the three dimensional orientations In Chemistry, an enantiomer ( from the Greek ἐνάντιος opposite and μέρος part or portion is one of two Stereoisomers that are nonsuperimposable Erythro redirects here For the fictional planet see Erythro (Asimov. [15] Identity of major products can usually be predicted, however.

In unsymmetrically substituted diene and dienophile, pseudo-ortho and para orientations in products are usually favored over meta orientation. Arene substitution patterns are part of Organic chemistry IUPAC nomenclature and pinpoint the position of Substituents other than Hydrogen in Arene substitution patterns are part of Organic chemistry IUPAC nomenclature and pinpoint the position of Substituents other than Hydrogen in Arene substitution patterns are part of Organic chemistry IUPAC nomenclature and pinpoint the position of Substituents other than Hydrogen in A particular preference in location of substitutents in the product can, in some cases, be explained in terms of frontier orbital theory. HOMO and LUMO are Acronyms for highest occupied Molecular orbital and lowest unoccupied Molecular orbital, respectively Most commonly, diene bears an electron-releasing group (ERG) and dienophile bears an electron-withdrawing group (EWG). Dienes or diolefins are Hydrocarbons which contain two double bonds. The Polar effect or electronic effect in Chemistry is the effect exerted by a Substituent on modifying Electrostatic forces operating on a nearby The Polar effect or electronic effect in Chemistry is the effect exerted by a Substituent on modifying Electrostatic forces operating on a nearby The strongest interaction takes place between HOMO of diene and LUMO of dienophile. HOMO and LUMO are Acronyms for highest occupied Molecular orbital and lowest unoccupied Molecular orbital, respectively HOMO and LUMO are Acronyms for highest occupied Molecular orbital and lowest unoccupied Molecular orbital, respectively Carbons that have the highest coefficients in two frontier orbitals will begin to bond; therefore these carbons will direct the orientation of substituents and thus identity of major product of a DA reaction.

Dealing with the actual frontier orbital coefficients can be avoided since the preferred orientation in product can be described in terms of partial positive and negative charges that exist in diene and dienophile. Carbon with a partial negative charge will interact most readily with carbon bearing a partial positive charge. Therefore those two carbons will start coming together, thus dictating the relative orientation of substituents. The existence of partial positive/negative charge can always be determined by drawing resonance contributors for diene and dienophile, taking their ERG and EWG into consideration.

The initial potential of the reaction was utilized in the form of insecticides, which ultimately led to the endo rule. Otto Diels’ and Kurt Alder’s reaction allowed for the production of weapons against agricultural pests to be fully realized in the 1930’s [16]. Most of these chemicals contained chlorine, of which two are called Dieldrin and Aldrin after the appropriate individuals. Dieldrin is a Chlorinated hydrocarbon originally produced in 1948 by J Aldrin is an organochlorine Insecticide which is oxidized in the Insect to form Dieldrin, a Neurotoxin. These chemicals have been long-since discontinued because of their toxicity to not only invertebrates, but to higher orders of organisms as well [17] [18]. Fortunately, insecticide use may continue unabated with the recent introduction of various safe treatments. Though insecticides like Dieldrin and Aldrin cause a slew of cardiac and respiratory illnesses (as well as reproductive failure) they served as an important step towards understanding why the endo product was the major yield. The study of the insecticide’s fused norcamphane rings became a highly popular topic in the 1930s and 1940s. Oxidative degradation revealed high specificity of the stereochemistry; after much research by Kurt Alder and H. F. Rickert, it became clear that steric hindrance is not as important in Diels-Alder reactions as it is in other reactions. This led to the secondary orbital explanation as well as a satisfactory hypothesis that elucidated polymerization of certain Diels-Alder adducts [19].


DA substituent effects
DA substituent effects

Cis principle

According to the cis principle or the Alder-Stein rules formulated by Alder and Stein in 1937, the stereochemistry of substituents in the starting material is retained in the product. Stereochemistry, a subdiscipline of Chemistry, involves the study of the relative spatial arrangement of Atoms within Molecules An important branch This means that if a cis-dienophile is reacted, both of the cis-substituents will end up on same side (face) of the product ring. In Organic chemistry, a substituent is an atom or group of atoms substituted in place of a Hydrogen atom on the Parent chain of a Hydrocarbon Trans-dienophile will yield a product where both of trans-substituents (that came originally from the dienophile) will be on different sides of the product ring. The same principle applies to dienes. Dienes or diolefins are Hydrocarbons which contain two double bonds. Trans, trans or cis, cis 1,4-substituents will end up on same side of the ring, whereas trans, cis 1,4-substituents will be oriented towards different faces of the ring.

Besides the ortho/meta/para-forming orientations, the diene and dienophile may arrange themselves in different ways to yield exo and endo transition states which result in different products. Dienes or diolefins are Hydrocarbons which contain two double bonds. Endo-exo isomerism is a special type of Isomerism found in Organic compounds with a Substituent on a bridged ring system The transition state of a Chemical reaction is a particular configuration along the Reaction coordinate. To determine which is the endo and which is the exo transition state, the two molecules are oriented parallel to each other, such that diene's single bond (one which connects two double bonds) is parallel to dienophile's double or triple bond. It makes no difference whether the dienophile is positioned above or below the diene. The single substituent (or cis-substituents on the dienophile) is oriented to point in the direction of diene's pi-system. This is the endo transition state (pictured below). If these substituents are pointed away from the diene, this would be the exo transition state. Dienes or diolefins are Hydrocarbons which contain two double bonds.

Endo addition rule

Endo versus exo effect
Endo versus exo effect

Using the 'cis principle' it is understood that cis-substituents on dienophile, for example, will end up on same side of the molecule. It is not obvious where the substituents on both diene and dienophile will end up relative to each other. In Organic chemistry, a substituent is an atom or group of atoms substituted in place of a Hydrogen atom on the Parent chain of a Hydrocarbon Dienes or diolefins are Hydrocarbons which contain two double bonds. To predict the cis or trans orientation of substituents that are coming from different molecules we have to examine possible transition states. The transition state of a Chemical reaction is a particular configuration along the Reaction coordinate. The most stable transition state will lead to the major product. Transition states will also dictate the relative orientation of the diene's and dienophile's substituents on the product ring. In some cases another rule can be applied: the endo addition rule. According to this rule, the most stable transition state results when there is a 'maximum accumulation of double bonds'. The transition state of a Chemical reaction is a particular configuration along the Reaction coordinate. This rule is not always followed. It most often applies when dealing with cyclic dienes and dienophiles. Dienes or diolefins are Hydrocarbons which contain two double bonds. For example, the DA reaction of cyclopentadiene and maleic anhydride yields over 95% of the endo product. Cyclopentadiene is a Chemical compound with the formula C5H6 This colorless liquid organic chemical has a strong Maleic anhydride ( cis -butenedioic anhydride toxilic anhydride dihydro-25-dioxofuran is an Organic compound with the formula C4H2O3 Endo-exo isomerism is a special type of Isomerism found in Organic compounds with a Substituent on a bridged ring system It is important to note that labels "exo" and "endo" relate to the orientation of substituents in the transition state and not to a specific orientation of substituents in the product molecule. In Organic chemistry, a substituent is an atom or group of atoms substituted in place of a Hydrogen atom on the Parent chain of a Hydrocarbon The transition state of a Chemical reaction is a particular configuration along the Reaction coordinate. In each individual case, the transition state has to be examined to see the most favored relative orientation of substituents. It is not true for the endo transition state that the substituents on dienophile and 1,4-substituents on diene will always point towards the same side of the newly formed ring. "Endo" and "exo" define specific transition states, not orientation of substituents. In the picture below, it just happens that the endo transition state will yield substituents on same side of the ring. This is not always so. In the case of maleic anhydride and cyclopentadiene the endo product will have the R groups of the diene and dienophile oriented toward the opposite sides of the newly formed ring. Maleic anhydride ( cis -butenedioic anhydride toxilic anhydride dihydro-25-dioxofuran is an Organic compound with the formula C4H2O3 Cyclopentadiene is a Chemical compound with the formula C5H6 This colorless liquid organic chemical has a strong Dienes or diolefins are Hydrocarbons which contain two double bonds.

Reaction with both exo-endo effect
Reaction with both exo-endo effect

The exo product can predominate, however, for some reactions. This can happen when the resulting endo product can easily dissociate back into the starting material. In such reactions, the exo product predominates with extended reaction times because the exo product is thermodynamically favored. Thermodynamic reaction control or kinetic reaction control in a Chemical reaction can decide the composition in a reaction product when competing reactions lead to In other cases, the endo product can convert to what would be the exo product of the reaction. In the example below, endo product B was the only one isolated after the Diels-Alder reaction. However, letting the reaction go for prolonged periods of time also yielded substantial amounts of exo product A. The authors speculated that endo product B can epimerize to exo product A in the following way:

Epimerization in DA reaction
Epimerization in DA reaction

In summary, diastereoselectivity is based on the postulation of the transition state. In Chemistry, epimers are Diastereomers that differ in configuration of only one stereogenic center Erythro redirects here For the fictional planet see Erythro (Asimov. The transition state of a Chemical reaction is a particular configuration along the Reaction coordinate. For any given DA reaction, one can imagine one possible transition state being favored over the other due to steric, stereoelectronic, and complexing factors. See also Intramolecular forces ' Steric effects arise from the fact that each Atom within a Molecule occupies a certain Thus, predictions can be made on the identity of major product of a particular DA reaction by looking at the starting material available.

Retro Diels-Alder reactions

DA reactions are reversible and in a retro Diels-Alder reaction the diene and alkene are reformed. One representative reaction is the Rickert-Alder reaction[20] in which, thanks to favorable rearomatization, the oxidized cycloadduct of quinone and 1,3-cyclohexadiene at elevated temperatures extrudes ethylene to form anthraquinone. "DDQ" redirects here DDQ is also the former callsign of a TV station in Toowoomba Queensland Australia Structure This Hydrocarbon has four Hydrogen Atoms bound to a pair of Carbon atoms that are connected by a Double bond. Anthraquinone ( 910-dioxoanthracene) is an aromatic Organic compound.

Rickert-Alder reaction

Asymmetric DA reactions

In asymmetric Diels-Alder reactions only one of two possible enantiomers is formed. Asymmetric catalysis by organocatalysis is possible with catalysts based on an imidazoline skeleton (the MacMillan catalyst) for instance in the reaction of cyclohexadiene with acrolein:[21]

DA reaction with MacMillan catalyst

Diels-Alder reactions also lend themselves to chiral synthesis with chiral auxiliaries. Asymmetric synthesis, also called chiral synthesis, enantioselective synthesis or stereoselective synthesis, is Organic synthesis which In Organic chemistry, the term Organocatalysis (a Concatenation of the terms "organic" and "catalyst" refers to a form of Catalysis Imidazoline is a Nitrogen -containing heterocycle derived from Imidazole. Acrolein (systematic name 2-propenal) is the simplest unsaturated Aldehyde. Asymmetric synthesis, also called chiral synthesis, enantioselective synthesis or stereoselective synthesis, is Organic synthesis which A chiral auxiliary is a Chemical compound or unit that is temporarily incorporated into an Organic synthesis so that it can be carried out asymmetrically with the In one research effort,[22] the auxiliary is derived from L-asparagine. Asparagine (abbreviated as Asn or N; Asx or B represent either asparagine or Aspartic acid) is one of the 20 most common natural The telescopic synthesis with cyclopentadiene and acrylic acid yields the DA adduct with three stereocenters as predominantly the endo conformer and with 54% ee. In Chemistry a one-pot synthesis is a strategy to improve the efficiency of a Chemical reaction whereby a Reactant is subjected to successive chemical reactions Cyclopentadiene is a Chemical compound with the formula C5H6 This colorless liquid organic chemical has a strong Acrylic acid or prop-2-enoic acid is a Chemical compound ( formula C 3 H 4 O 2 and it A stereocenter, or stereogenic centre, is any Atom in a Molecule bearing groups such that an interchanging of any two groups leads to a Stereoisomer Endo-exo isomerism is a special type of Isomerism found in Organic compounds with a Substituent on a bridged ring system Enantiomeric excess exists where one Enantiomer is present more than the other in a Chemical substance, and is defined as the absolute difference between the mole

Asymmetric Diels-Alder reaction with asparagine auxiliary

Lewis acids (AlCl3, ZnCl2, and others) act as catalysts by coordinating to the dienophile. Aluminium chloride (AlCl3 is a compound of Aluminium and Chlorine. Zinc chloride is the name of Chemical compound with the formula Zn[[chlorine Cl]]2 and its hydrates The complexed dienophile becomes more electrophilic and more reactive toward the diene. In Chemistry, an electrophile (literally electron-lover) is a Reagent attracted to Electrons that participates in a chemical reaction by accepting This increases the rate and often the stereoselectivity of a DA reaction.

References

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  20. ^ Alder, K. ; Stein, G. ; Pries, P. ; Winckler, H. Ber. Dtsch. Chem. Ges. 1929, 62B, 2337-72.
  21. ^ New Strategies for Organic Catalysis: The First Highly Enantioselective Organocatalytic Diels-Alder Reaction Ahrendt, K. A. ; Borths, C. J. ; MacMillan, D. W. C. J. Am. Chem. Soc.; (Communication); 2000; 122(17); 4243-4244. The Journal of the American Chemical Society (usually abbreviated as J doi:10.1021/ja000092s
  22. ^ A fully-telescoped, aqueous, auxiliary-mediated asymmetric transformation Mathew P. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. D. Mahindaratne, Brian A. Quiñones, Antonio Recio III, Eric A. Rodriguez, Frederick J. Lakner, and George R. Negrete Arkivoc(EJ-1566C) pp 321-328 2005. Arkivoc (print- ISSN 1424-6376 CODEN AGFUAR stands for Archive for Organic Chemistry and is an online Open access (Article)

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Dictionary

Diels-Alder reaction

-noun

  1. (organic chemistry) The cycloaddition reaction between a conjugated diene and an alkene to form a cyclohexene ring.
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