Diels Alder Reaction

12 Key excerpts on "Diels Alder Reaction"

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  Macroscale and Microscale Organic Experiments

  • Kenneth Williamson, Katherine Masters(Authors)
  • 2016(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  619 Diels–Alder Reaction CHAPTER 48 PRE-LAB EXERCISE: Describe in detail the laboratory operations, reagents, and solvents you would use to prepare. Otto Diels and his pupil, Kurt Alder, received the Nobel Prize in Chemistry in 1950 for their discovery and work on the reaction that bears their names. Its great usefulness lies in its high yield and high stereospecificity. Acycloaddition reaction, the Diels–Alder reaction involves the 1,4-addition of a conjugated diene in the s-cis conformation to an alkene in which two new s (sigma) bonds are formed from two p (pi) bonds. The adduct is a six-membered ring alkene. The diene can have the two conjugated bonds contained within a ring system, as with cyclopentadiene or cyclohexadiene, or the molecule can be an acyclic diene that must be in the cis conformation about the single bond before reaction can occur. s-trans s-cis Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 620 Macroscale and Microscale Organic Experiments The reaction works best when there is a marked difference between the electron densities in the diene and the alkene with which it reacts—the dienophile. Usually, the dienophile has electron-attracting groups attached to it, whereas the diene is electron rich, for example, as in the reaction of methyl vinyl ketone with 1,3-butadiene. Retention of the configurations of the reactants in the products implies that both new s bonds are formed almost simultaneously.

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  Experimental Organic Chemistry

  A Miniscale & Microscale Approach

  • John Gilbert, Stephen Martin(Authors)
  • 2015(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  In this reac-tion, the alkene partner is generally referred to as a dienophile. This cycloaddi-tion reaction is called the Diels-Alder reaction in honor of Otto Diels and Kurt Alder, the two German chemists who recognized its importance and shared the 1950 Nobel Prize in Chemistry for their extensive development of this reaction. A more detailed account of their elegant work is included in the Historical High-light Discovery of the Diels-Alder Reaction, which is available online. The Diels-Alder reaction also belongs to a class of reactions termed 1,4-additions, because the two new carbon-carbon s -bonds are formed between the 1- and 4-carbon atoms of the diene and the two p -bonded carbon atoms of the dienophile. 12 Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 422 Experimental Organic Chemistry ■ Gilbert and Martin A cycloadduct A dienophile A 1,3-diene 1 2 3 4 1 2 3 4 (12.1) The scope of the Diels-Alder reaction is broad, and many combinations of di-enes and dienophiles are known to furnish cycloadducts in good yields. The pres-ence of electron-withdrawing substituents such as cyano, C ≡ N, and carbonyl, C = O, groups on the dienophile increases the rate and yield of the reaction. The Diels-Alder reaction is remarkably free of complicating side reactions, and yields of the desired product are often high. Probably the single most important side reac-tion that may be encountered is dimerization or polymerization of the diene and/ or dienophile.

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  Stereoselective Organocatalysis

  Bond Formation Methodologies and Activation Modes

  • Ramon Rios Torres(Author)
  • 2013(Publication Date)
  • Wiley

    (Publisher)

  The bond changing process must be concerted in order for a reaction to fit the category of pericyclic reactions; however, it is often difficult to distinguish between a pericyclic and a stepwise mechanism of a cycloaddition. In this chapter the main focus will be on reactions that proceed, or are most likely to proceed, through a concerted mechanism; we will, however, include some exceptions for entirety. The majority of stepwise cycloaddition reactions will be discussed in Chapters 10 and 16. This review is not intended to be comprehensive, but instead organocatalytic pericyclic reactions will be outlined in the context of their utility in synthetic chemistry.

  6.2 Diels–alder Reactions

  The Diels–Alder reactions provide a highly attractive and rapid approach toward dense functionalized cyclohexane structures that allows, in principle, for the formation of four contiguous asymmetric centers in one reaction step. Relative stereochemistry is often well-defined due to a cyclic transition state determined by primary and secondary frontier orbital interaction. Interestingly, the first asymmetric catalytic Diels–Alder reaction based on a chiral Lewis acid complex was reported as early as 1963 [1]. Since then, the use of chiral auxiliaries and chiral Lewis acid catalysis has evolved to well-established and reliable synthetic strategies. The first enantioselective organocatalytic Diels–Alder reaction was reported by Riant and Kagan [2] as early as 1989 involving the HOMO activation of anthracenone 1 using cinchona alkaloid 5 (Scheme 6.1 ) [3, 4]. Although an important proof of concept, this work had limited synthetic applications due to poor selectivity and generality. In 2006, Tan and co-workers [3] improved the enantioselectivity of this reaction by using guinadinine 6 as a catalyst to give 4 in over 90% ee; and during the last 10 years, several powerful asymmetric organocatalytic Diels–Alder reactions have emerged.

  Scheme 6.1 Chiral base catalyzed Diels-Alder reaction of anthracenone.

  The real breakthrough and pioneer work was accomplished by MacMillan and co-workers [5] in 2000. They reported the first highly selective asymmetric organocatalytic Diels–Alder reaction between 2-enals 8 and cyclopentadiene 7 catalyzed by imidazolidinone 10 to give the Diels–Alder adduct 9 (Scheme 6.2 ). The catalytic cycle involves initial iminium ion formation, thus lowering the LUMO of the dienophile enabling the cycloaddition. The enantioselectivity is rationalized by the shielding of the re face of the dienophile by the benzyl group on the catalyst framework, leaving the si face exposed for cycloaddition (see Chapter 2 for further details) [6, 7]. The reaction is tolerant to different 2-enals, having both alkyl and aryl groups, and the products are obtained in high yield and enantioselectivity. Unfortunately, under these reaction conditions no endo/exo

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  High Pressure Organic Synthesis

  • Davor Margetic(Author)
  • 2019(Publication Date)
  • De Gruyter

    (Publisher)

  2Diels –Alder cycloaddition reactions Introduction 2.1DA cycloaddition reactions 2.2Heterocyclic dienes 2.2.1Five-membered dienes 2.2.2Six-membered dienes 2.3HDA reactions 2.4Intramolecular DA reactions 2.5RDA reactions 2.6Homo-Diels–Alder reactions 2.7Tandem DA reactions 2.8Selectivities of DA reactions 2.9Asymmetric reactions 2.10Natural product synthesis 2.11DA reactions of fullerenes References Introduction

  The formation of six-member rings by the Diels–Alder (DA) cycloaddition reactions is of great synthetic importance and represents the most often performed reaction in high-pressure (HP) conditions. From way back in 1939, it is known that DA reaction is accelerated by pressure [1]. The applications of HP-DA reactions vary from medicinal chemistry, natural product synthesis [2] to material science. There is an enormous volume of literature concerned with cycloadditions under pressure. Literature shows that even the highly unreactive aromatics such as naphthalene [3], anthracene [4], benzene[5, 6] and [2,2]paracyclophane could react as dienes at elevated pressures [7].

  DA reactions are characterized by very large negative activation volumes. This suggests that [4 + 2] cycloadditions are highly favored by the application of pressure and can be interpreted as the following one-step concerted mechanism, which is characterized by a “quasi-cyclic” transition state with simultaneous formation of two covalent bonds [8]. For example, ΔV ≠ for isoprene reaction with quinones range from –38.1 to –32.2 cm3 mol−1 in EtOH and –37.2 to –35.3 cm3 mol−1 in CHCl3 [9]. In a mechanistic study of DA reactions under HP conditions (6.1 kbar) by Grieger and Eckert [10], ΔV ≠ were obtained as follows: for the addition of 1,3-cyclohexadiene with maleic anhydride, it is –37.2 cm3 mol−1 in DCM; for addition of cyclopentadiene (CPD) with dimethyl acetylenedicarboxylate, it is –30.2 cm3 mol−1 in EtOAc; for isoprene with maleic anhydride, it is –39.0 cm3 mol−1 in acetone; and for trans -1-methoxy-1,3-butadiene-maleic anhydride, it is –45.4 cm3 mol−1 in n -butyl chloride. Activation volumes could also be affected by the solvent. For the reaction of 9-anthracenemethanol and N -ethylmaleimide, the following activation volumes are obtained: ΔV ≠ = –36.0, –31.4 and –22.4 cm3 mol−1 in water, butan-1-ol and heptane, respectively [11]. The largest ΔV ≠

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  Asymmetric Synthetic Methodology

  • David John Ager, Michael B. East(Authors)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)

  55

  Aside from the regiochemistry, Diels-Alder adducts may be formed by two types of approach: The most favored adduct is generally the endo isomer even though the exo addition product is thermodynamically preferred. This is referred to as the endo, or Alder, rule and can be aided by the addition of a Lewis acid catalyst [2.5.2]. This preference for the endo adduct has been attributed to additional stability gained by secondary molecular orbital overlap (Figure 12.1 ).52 ,

  56 ,

  57

  FIGURE 12.1.

  Secondary molecular orbital interactions for the Diels-Alder reaction of cyclopentadiene with maleic anhydride

  The Diels-Alder reaction is stereoselective; the relative stereochemistry of the dienophile is maintained in the product through syn addition. Hence, dimethyl maleate and dimethyl fumarate react with butadiene to yield the cis and trans isomers of the cyclohexene adduct, respectively (Scheme 12.1 ). Selectivity is also observed when there is a preference for the Si- or Re-face of the diene or dienophile during the cycloaddition.

  7 ,

  8 ,

  9 , 12 Where both the diene and the dienophile exhibit a preference, double asymmetric induction can be observed.31 , 58 , 59

  SCHEME 12.1.

  12.1.2. CHIRAL DIENOPHILES

  Chiral dienophiles provide the vast majority of examples of asymmetric Diels-Alder reactions and, of these, acrylates are the most common (Table 12.1 ).31 The use of a chiral auxiliary or group on the dienophile can provide for face selectivity. Chiral dienophiles have been divided into two categories: type I and type II reagents (Figure 12.2 ). Type I reagents, such as chiral acrylates, can incorporate a chiral group in a simple and straightforward manner. Type II reagents, where the chiral group is one atom closer to the double bond,31

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  Progress in Heterocyclic Chemistry

  • Gordon Gribble, J. Joule, Gordon W. Gribble(Authors)
  • 2011(Publication Date)
  • Elsevier Science

    (Publisher)

  Chapter 1

  The Diels-Alder cycloadditions of 3,5-dibromo-2-pyrone and its derivatives

  Heui-Yeon Kim; Cheon-Gyu Cho, * [email protected]     Department of Chemistry, Hanyang University, Seoul, Korea

  1.1 OVERVIEW OF THE DIELS-ALDER CHEMISTRY OF 2-PYRONE

  As one of the classical 1,3-dienes investigated by Diels and Alder <31A257 >, 2-pyrones are synthetically useful synthons which can provide various carbocyclic frameworks in the single chemical operation called the Diels-Alder cycloaddition <92TL9111 ; 99AC47 >. However, due to the inherent partial aromatic character, the parent unsubstituted 2-pyrone 1 itself does not undergo cycloadditions as readily as do other cyclic 1,3-dienes. Cycloadditions often require high reaction temperatures which can cause concomittant CO2 extrusion from the bicyclolactone 2 , furnishing dihydrobenzenes or aromatized products 3 (Scheme 1 ).

  Scheme 1 Diels-Alder cycloaddition of 2-pyrone 1

  The reaction sequence in Scheme 1 is a viable synthetic protocol, utilized in the synthesis of various aromatic natural products including lasalocid A <83JACS1988 >, rufesine <84JOC4050 >, juncusolare <84JOC4033 >, among many others. The initially formed bicyclolactone 2 has further synthetic utility, because of the stereochemically controlled rich functionality resulting from the cycloaddition reaction. Some notable applications can be found in total syntheses of taxol <95JACS634 >, shikimic acid <86JACS7373 >, natural/unnatural sugars and a series of vitamin D3 analogs <95OS231 >.

  Various strategies have been developed to arrest the cycloadditions at the bicyclolactone stage. Performing the reactions in the presence of a Lewis acid or under high pressure can lower the reaction temperature to allow the isolation of the bicyclic lactones. In some cases, using geometrically constrained dienophiles or templates like phenylboronic acid have effectively suppressed the CO2

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  Organic Chemistry

  • David R. Klein(Author)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  In other words, the reverse reaction (a retro Diels–Alder) will be thermodynamically favored at high temperature. In summary, Diels–Alder reactions are generally performed at moderate temperatures, usually between room temperature and 200°C, depending on the specific case. The Dienophile The starting materials for a Diels–Alder reaction are a diene and a compound that reacts with the diene, called the dienophile: X Diene Dienophile We will begin our discussion with the dienophile. When the dieno- phile does not contain any substituents, the reaction exhibits a large activation energy and proceeds slowly. If the temperature is raised to overcome the energy barrier, the starting materials are favored over the products, and the resulting yield is low. 20% 200°C + 16.7 Diels–Alder Reactions 719 A Diels–Alder reaction will proceed more rapidly and with a much higher yield when the dienophile has an electron- withdrawing substituent such as a carbonyl group. The carbonyl group is electron withdrawing because of resonance. Can you draw the resonance structures? Other examples of dienophiles that possess electron- withdrawing substituents are shown here. When the dienophile is a 1,2-disubstituted alkene, the reaction proceeds with stereospecificity. Specifically, a cis alkene produces a cis disubstituted ring, and a trans alkene produces a trans disub- stituted ring: X X X X X X X X + + + En A triple bond can also function as a dienophile, in which case the product is a ring with two double bonds (a 1,4-cyclohexadiene). O OR O OR OR O OR O + O H H O 100% + O R O OR CN O OH STEP 1 Redraw and line up the ends of the diene with the dienophile. STEP 2 Draw three curved arrows, starting at the dienophile and going either clockwise or counterclockwise. BY THE WAY It is not necessary to draw the dotted lines between the diene and the dienophile, but you might find it helpful.

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  Advances in Alicyclic Chemistry

  • Harold Hart, G. J. Karabatsos, Harold Hart, G. J. Karabatsos(Authors)
  • 2013(Publication Date)
  • Academic Press

    (Publisher)

  Using methacrolein dimer (XLVI) as the prototype, this common species may be pictured as (XLVII) where bond b-c remains intact during reaction, whereas d-h is weakened with concurrent partial bond ΐ -0 4$ (51) CH 3 (XLVI) (XLVIIa) The Mechanism of the Diels-Alder Reaction 41 formation at a-f. Other structures, similar to (XLVIIa) contributing to the resonance hybrid of this species might be (XLVIIb) and (XLVIIc). Continuing H > :': CH 3 ? / H '' // CH 3 o (XLVIIb) H /-v ' CH 3 ^v H CH3O (XLVIIc) along the energy surface from this common intersection, the two reactions diverge. The retro Diels-Alder path continues by rupture of b-c to produce addenda. 94 If structures (XLVIIb) and (XLVIIc) have any validity in the mechanism of the Diels-Alder reaction, they suggest that 1,2-cycloaddition of a diene with a dienophile may also share a common transition state or intermediate. The competing reaction of 1,2- and 1,4-addition of tetracyanoethylene to 4-methyl-l,3-pentadiene [Eq. (52)] was studied by Stewart. 95 In tetrahydro-furan solution at room temperature the ratio of products of 1,2- to 1,4-addition is 69 : 11, respectively. The ratio changes slightly with temperature (CH 3 ) 2 C=CH-CH=CH 2 + (NC) 2 C=C(CN) 2 ► (CH 3 ) 2 C=CH —1 i(CN) 2 ' '(CN) 2 + (XLViii) ( 5 2 ) (CH 3 )2 1(CN) 2 J (CN) 2 (XLIX) so as to yield a difference in enthalpy of activation of 1.4kcal/mole. In cyclohexane, however, the yield of 1,4-product increases by a factor of three, whereas in a polar solvent such as nitromethane, reaction is very rapid and only the 1,2-product can be detected. 94 The forward reaction may proceed in one of two ways : (1) Bond b-c may strengthen to a full bond and perhaps represent a decrease in free energy with respect to the transition state preceding it. In other words, (XLVII) represents an intermediate; or (2) bond h-d or a-f may strengthen before b-c becomes a full bond.

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  Advances in Cycloaddition

  • Michael Harmata(Author)
  • 1999(Publication Date)
  • JAI Press

    (Publisher)

  The resulting cyclohexadiene then suffers elimination or dehydrogenation leading to aromatic products (vide supra) or cycloaddition of a second dieno- phile molecule leading to bicyclo[2.2.2]octenes (vide infra). If the dienophile is geminally disubstituted or otherwise unable to aromatize and if the cyclohexadiene does not undergo subsequent cycloaddition, dihydrobenzene products may be isolated. This reaction mode is less common than that leading to aromatic products, but some examples are detailed in the 1974 and 1992 reviews. 2'3 A more recent example of this methodology is the Diels-Alder reaction of 3-carbomethoxy- 2-pyrone 21 with ct-terpinene, followed by CO z extrusion leading to bicycle 22, which was subsequently elaborated to (+)-10-epijuneol. 23 .C02 Me / C02Me / [~ O~]~H L 64~ 21 22 (• C. Double Diels-Alder Cycloadditions When at least two equivalents of dienophile are used and the reaction conditions are such that CO 2 extrusion spontaneously occurs, a second molecule of dienophile adds to the cyclohexadiene initially produced. A number of examples of this sort of reaction have been reported, generally in which maleic anhydride or maleimides function as the dienophile. Klemm and co-workers have applied this double Diels-Alder methodology to the synthesis of novel polymers. 24 Copolymerization of bispyrone 23 with bismaleimide 24 leads to soluble, stable poly- mers of number-average molecular weights between 10,000 and 34,000. The polymers are composed of coronand structure subunits 25 alternating with alkyl linkers. The structure of the coronand subunit, including the endo-selectiv- ity of these double Diels-Alder adducts, has been elegantly demon- strated in model reactions. The orientation of the unsymmetrical Diels-Alder Cycloadditions of 2-Pyrones ! 0 + o I S 23 24 -O N, .O R O,,, N O 25 H2) O _ ~1~ R---- N-'~O Un 55 bismaleimide linker is unknown.

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  Strategies and Tactics in Organic Synthesis

  • Michael Harmata(Author)
  • 2011(Publication Date)
  • Academic Press

    (Publisher)

  Other dienophiles (maleic anhydride and 4-phenyl-[1,2,4]-triazole-3,5-dione) also reacted with 45f to give mixtures of diastereomeric products similar to 55 . Although the cycloaddition reaction of 45f affords a complex molecular scaffold in a rapid manner, obtaining the product as a mixture of diastereomers was dis-couraging. Furthermore, biological testing of compounds as diastereomeric mixtures is not ideal due to variability in the assay concentrations. Even though separation of the diastereomers by HPLC was feasible, it would be costly and time consuming when preparing a larger-scale library. Therefore, controlling the chemo- and diastereoselectivity of the Diels–Alder reaction of the triene was important, and a new strategy for tandem intermolecular cycloaddition was considered. V. Design and Synthesis of a Second Generation Triene Our efforts to control the selectivity of the Diels–Alder reactions focused on designing a new triene. It was reasoned that constraining the appended ester as part of a ring would reduce the steric bulk from the C2 position and, therefore, increase the reactivity of the diene involved in the first Diels–Alder reaction. Moreover, the cyclic constraint of the ester may block one face of the sterically biased triene with the R 1 group. Finally, the rate of the second Diels–Alder reaction could be slowed by placing an electron withdrawing carbonyl group at the C6 position. Structures such as the novel imidazo–pyridinone triene 58 address all of these issues (Scheme 18). Putting the synthesis of 58 into practice required examination of the Rh(I)-catalyzed cycloisomerization of amide-tethered allenyne 56 to form -lactam triene 57 . Traditionally, lactams are synthesized via carbon–nitrogen bond formation. For example, lactams are formed via dehydration of amino acids, 65 by cyclization of an amide onto an alkene, 66 alkyne 67 or an allene, 68 and intramolecular vinylation of amides.

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  Theoretical Organic Chemistry

  • C. Párkányi(Author)
  • 1997(Publication Date)
  • Elsevier Science

    (Publisher)

  The Diels-Alder transition state has an energy of activation that is 2.3 kcal/mol lower than the energy of the Michael type of transition state structure (Figure 5). Diels-Alder TS Michael TS Figure 5. Two possible transition state for reaction between diformylacetylene and 1-formyl-2,5-dimethylpyrrole. We can summarize that, generally, derivatives of pyrrole do not react with low or moderately reactive dienophiles such as acetylene. There are at least two reasons: FMO energies are too low (HOMO) or too high (LUMO) and pyrrole has 529 high aromatic character (very uniform ring bond orders). Substituents at the C(1) position can substantially decrease the aromatic character of pyrrole and consequently increase its reactivity. Nevertheless, reactive dienophiles such as diformylacetylene are necessary for the reaction. If pyrrole does not have substituents at the C(2) and C(5) position, formation of Michael type adducts might be preferred. To get a qualitative picture of the reaction potential, a single point B3LY/6-31G(d) computational study is required. Our computational study is in complete agreement with experimental data. 3.4. Diels-Alder reactions with benzo[b] and benzo[c]-fused heterocycles Five-membered heterocyclic compounds with a fused benzene ring are, from a theoretical point of view, ideal starting materials for the preparation of complex organic compounds that contain a 1,2-disubstituted benzene ring. One possible transformation begins with benzene[c]-fused heterocycles through a Diels-Alder reaction with acetylene derivatives. The formed cycloadduct can be ozonized; the furan ring can be easily opened generating the desirably functionalized 1,2- disubstituted benzene (Scheme 3). Some theoretical studies pertaining to the R1 X R2 R3 0 ii I + ~ ,,~ R4 --~- --~. CHO R 1 R4 R 3 Scheme 3. Possible transformation of a benzo-fused heterocycle into 1,2- functionalized benzene derivatives.

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  Science of Synthesis: Metal-Catalyzed Cyclization Reactions Vol. 2

  • Shengming Ma, Shuanhu Gao(Authors)
  • 2016(Publication Date)
  • Thieme

    (Publisher)

  The resulting soln was stirred at 60 8 C for 0.5 h and the reaction was then quenched with sat. aq NaHCO 3 (2 mL). This mixture was extracted with CH 2 Cl 2 and the usual workup gave a residue, which was purified by chromatography (silica gel, hex-ane/EtOAc 1:1) to give a colorless solid; yield: 125.6 mg (94%); 94% ee. 2.5. 2 Oxa-Diels–Alder Reactions Generally, two different mechanistic pathways are taken into account for the Lewis acid catalyzed oxa-Diels–Alder reaction: one is a traditional concerted Diels–Alder cycloaddi-tion, and the other is a stepwise Mukaiyama aldol reaction pathway (Scheme 20). For ex-ample, the reaction of benzaldehyde with 1-methoxy-2-methyl-3-(trimethylsiloxy)penta-1,3-diene using boron trifluoride as a Lewis acid catalyst proceeds via the stepwise Mu-kaiyama pathway, while the reaction proceeds via the concerted Diels–Alder route using zinc(II) chloride or lanthanides. [33] In the stepwise Mukaiyama pathway the major product has a 2,3-trans configuration, while in the concerted Diels–Alder pathway the reaction af-fords the 2,3-cis -product exclusively. In general, the reaction pathway in hetero-Diels– Alder reactions using chiral Lewis acid catalysts is proposed on the basis of the intermedi-ate formed and the stereochemistry observed. Scheme 20 Reaction Pathways for an Oxa-Diels–Alder Reaction + PhCHO O MeO OTMS Ph MeO Ph O OTMS O O Ph OMe TMSO Mukaiyama aldol pathway Diels − Alder pathway 224 Metal-Catalyzed Cyclization Reactions 2.5 Asymmetric (Hetero-)Diels–Alder Reactions 2.5. 2.1 Reaction Using Chiral Aluminum Complexes The enantioselective oxa-Diels–Alder reaction between various Danishefsky-type dienes and aldehydes, catalyzed by chiral organoaluminum complex 40 , which is derived from a 3,3 ¢ -disubstituted 1,1 ¢ -binaphthalene-2,2 ¢ -diol and trimethylaluminum, gives the de-sired 2,3-dihydro-4 H -pyran-4-one derivatives 41 in high yield and with up to 95% enantio-meric excess (Scheme 21).

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