Diels-Aider reaction

Diels-AIder reactions, I, 618 reactions, 1, 617-620 synthesis, 1, 614-616 2-Germoxetanes heterosubstituted germacyclobutanes and, 1, 596 Gewald synthesis thiophenes, 4, 888-889 ( )-Gingerol synthesis, 1, 453 (+)-(S)-Gingerol synthesis, I, 435 Ginkgolide A... 

Table 11.4 Relative Reactivity of Substituted Butadienes in tbe Diels-Aider Reaction"...

The Chiral Lewis Acid-catalyzed Diels-AIder Reaction... 

The Asymmetric Diels-AIder Reaction of a,jS-Unsaturated Aldehydes as Dienophiles 1.2.1.1 Aluminum... 

Chiral aluminum catalyst 2, prepared from Et2AlCl and a Vaulted biaryl ligand, is reported to be an effective Lewis acid catalyst of the Diels-AIder reaction between methacrolein and cyclopentadiene, affording the adduct in 97.7% ee [4] (Scheme 1.2). Although the Diels-AIder reaction with other a,/ -unsaturated aldehydes has not been described, that only 0.5 mol% loading is sufficient to promote the reaction is a great advantage of this catalyst. 

In 1989 Yamamoto et al. reported that the chiral (acyloxy)borane (CAB) complex 3 is effective in catalyzing the Diels-AIder reaction of a number of a,/ -unsaturated aldehydes [5]. The catalyst was prepared from monoacylated tartaric acid and bo-... 

Diels-Alder reactions in which nitroalkenes act as dienophiles are acceleratedin thepresence of 4 M l.iClOi) in nitromethane This acceleration is higher than that observed when l.iClO is used in diethyl ether The diastereoselecdve Diels-Aider reaction using homochiial nitroalkenes shown in Eq 8 31 has been demonstrated... 

The Mayo mechanism involves a thermal Diels-AIder reaction between two molecules of S to generate the adduct 95 which donates a hydrogen atom to another molecule of S to give the initiating radicals 96 and 97. The driving force for the molecule assisted homolysis is provided by formation of an aromatic ring. The Diels-AIder intermediate 95 has never been isolated. However, related compounds have been synthesized and shown to initiate S polymerization."110... 

Keywords it-Facial selectivity, a/ir Interaction, CH/ir Interaction, Ciplak effect, Diels-AIder reaction, Electrostatic interaction, Orbital mixing rule. Orbital phase environment, Secondary orbital interaction, Steric repulsion, Torsional control... 

Compounds containing a double or triple bond, usually activated by additional unsaturation (carbonyl, cyano, nitro, phenyl, etc.) in the ap position, add to the 1 4-positions of a conjugated (buta-1 3-diene) system with the formation of a six-membered ring. The ethylenio or acetylenic compound is known as the dienophile and the second reactant as the diene the product is the adduct. The addition is generally termed the Diels-AIder reaction or the diene synthesis. The product in the case of an ethylenio dienophile is a cyctohexene and in that of an acetylenic dienophile is a cyclohexa-1 4-dlene. The active unsaturated portion of the dienophUe, or that of the diene, or those in both, may be involved in rings the adduct is then polycyclic. 

Diels-AIder reactions were utilized to prepare isoquinoline derivatives. Various tetrahydroisoquinoline-3-carboxylic acid derivatives were prepared by an enyne metathesis followed by a Diels-AIder reaction. For example the enyne 71 was treated with Grubb s catalyst to afford diene 72 in 65% yield. Subsequent Diels-AIder reaction and oxidation gave tetrahydroisoquinoline 73 in 93% yield <0OCC5O3>. Dihydrosoquinoline 75 was prepared... 

Figure 5.63 The NRT bond-order-bond-length correlations for Ci—C2 (triangles), C2—C3 (squares), C —C5 (circles), and C5—C6 (plus signs) bonds in the model Diels-AIder reaction (see Fig. 5.59(a) for the atom numbering).

Cyclic disulfides.1 Singlet sulfur is generated when 2,2 -dithiobenzoylbiphenyl is heated at 80-130° with formation of 9,10-diphenylphenanthrene (equation I). The S2 can be trapped by a Diels-AIder reaction with 1,3-dienes to form cyclic disulfides in 60-85% yield. 

TaM 18, Intramolecular Diels-AIder reactions under high pressure of furfuryl-substituted alkylidenecyclopropanes 195... 

A further useful reaction sequence, reported by Aumann [219], is based on the Diels-Alder reaction of 2-pyranylidene complexes with enamines (Figure 2.36). Retro-Diels-AIder reaction of the initially formed 3-oxabicycIo[2.2.2]octan-2-ylidene complex leads to elimination of metal hexacarbonyl and formation of a substituted cyclohexadiene. Although this sequence can also be performed with the corresponding carbonyl compounds (2//-2-pyranones), these normally... 

In the ET-catalyzed Diels-AIder reaction of indole with 1,3-cycIohexadiene a stepwise mechanism was derived on the basis of kinetic isotope effects. In light of B3LYP/6-31G calculations, these effects support a stepwise mechanism, initiated by attack of the diene on the 3-position of indole. ... 

Acceleration of a Diels-AIder reaction by a self-assembled dimeric capsule... 

The nucleophilic 7V,ALdiethyI-l-propynamine adds across the C=C bond of 31 at 20° C to yield the adduct 187, whereas the electrophilic diphenyl-ketene adds across the N=N bond at -8°C to give 188 (97%).167 This difference in behavior finds a parallel in the Diels-AIder reactions (Section IV.E.l). 

On heating with cyclopropenone 113 (Scheme 28), 59 gives equal amounts of two products 114 arises from a Diels-AIder reaction, and 115 from direct attack of the pyrazole nitrogen at the carbonyl group.77... 

Pyridine unnelatum. 1,2,4-Triazine can function as a reactive azadicnc in Diels-Aider reactions with enamines, particularly pyrrolidine enamines, to form substituted pyridines. 

Dichlorothiophene-l,1-dioxide undergoes Diels-AIder reactions with butadiene and isoprene to give mixtures of 115a and 116a and... 

In Diels-AIder reactions a nitroolefin may function as an electron-deficient ene com-onent or a 1,2-dihydropyridine derivative may be used as a diene component. Both types of eactants often yield cyclic amine precursors in highly stereoselective manner (R.K. Hill, 1962 i. Biichi, 1965, 1966A). 

The Diels-AIder reaction of o-quinodimethanes (from benzocydobutenes) with nitrogen-ubstituted enes has also been applied to alkaloids synthesis (see p. 280f T. Kametani, 1972, 1973, 1974 W. Oppolzer, 1978 A). 

A.2.2. Asymmetric Diels-AIder Reactions with Acryloyl Oxazolidinones... 

With Chiral Bis(oxazoline)/metal Complexes Several research groups have developed chiral Lewis acids by using chiral 1,3-bis(oxazoline) ligands for asymmetric Diels-AIder reactions. Evans designed C2-symmetric bis(oxazoline)/Cu(II) complexes derived from chiral bis(oxa-zoline)and Cu(OTf)2, and applied them to asymmetric cycloadditions of acryloyl oxazolidinones and thiazolidine-2-thione analogues. Attractive features of this catalyst system include a clearly interpretable geometry for the catalyst-dienophile complex, which rationalizes the sense of asymmetric induction for the cycloaddition process [26] (Eq. 8A.14). 

Diels-AIder reaction with Lewis acid (MgBr2 or C2H5 A1C12) proceeds stereospecifically to give cra/o-adducts in which the phenylthio function is oriented ortho to the carbonyl group (7, 75-76). The related dienes 2 and 3 undergo cycloaddition with similar stereo- and regiospecificity. 

Mels-Alder catalyst AlCl is useful for activation of allenic esters in Diels-Aider reactions and for increasing the emfo-selectivity.5 I MitnpIe ... 

Domino-Knoevenagel-carbon-Diels—Aider Reactions I 161... 

Enantioselective triplex Diels-AIder reaction. 1,3-Cyclohexadiene is known to undergo Diels-AIder reactions with electron-rich dienes when irradiated with arene sensitizers. The reaction is presumed to involve a triplex involving the sensitizer (15, 129). The first enantioselective example of this Diels-AIder reaction has been achieved using (-)-l as sensitizer. Thus irradiation of 1,3-cyclohexadiene with trans-P-methylstyrene in the presence of (-)-l at -65° provides the endo-adduct 2 in 15% ee (equation I). The enantioselectivity decreases with an increase of the temperature, being 1% at 25°. 

Oppolzer s chiral auxiliary,6 (-)-2,10-camphorsultam, is useful in the asymmetric Diels-Aider reaction,3.4 and for the preparation of enantiomerically pure p-substituted carboxylic acids7 and diols,8 in the stereoselective synthesis of A2-isoxazolines,9 and in the preparation of N-fluoro (-)-2,10-camphorsultam, an enantioselective fluorinating reagent.10... 

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