Diels-Alder catalysts chloride

DIELS-ALDER CATALYSTS Boron trifluoride. Boron irifluoride etherate. Ethylaluminum dichloride. Silica gel. Stannic chloride. Titanium(IV) chloride. Tris(p-bromophenyl)aminium hexa-chlorostibnatc. 

Diels-Alder catalysts Alkylaluminum halides, 5, 173 Boron trifluoride etherate, 43 Diethylaluminum chloride, 173 Dimethylaluminum chloride, 5 Sodium dodecyl sulfate, 281 Titanium(IV) chloride-Diethylaluminum chloride, 309... 

DIELS-ALDER CATALYSTS Alkylaluminum halides. Alumina. Aluminum chloride. Bomyloxyaluminum chloride. Copper(n) acetate-Copper(II) tetrafluoroborate. 3-Cyclodextrin. 

Dieckmann cvclization Dimethyl sulfoxide. Potassium t-butoxide. Potassium ethoxide. Diels-Alder catalyst Aluminum chloride. 

Diels-Alder catalyst [1, 31-32, after line 8], Ciganek (Du Pont) found thal aluminum chloride strongly accelerates the Diels-Alder reaction of benzene with dicyanoacetylene.338 In the presence of this Lewis acid the reaction proceeded at room temperature to furnish the adduct (1) in 63% yield and smaller amounts of the Friedel-Crafts products phenylmaleonitrile (2) and phenylfumaronitrile (3). In the absence of aluminum chloride the adduct (1) was produced in yield of only 14% after a reaction period of 2 days at 180°. 

Diels-Alder catalyst, 1, 31-32 2, 21-22. The Diels-Alder reaction of 1-carbo-methoxypyrrole (1) with dimethyl acetylenedicarboxylate catalyzed by aluminum chloride gives 2,3,7-tricaibomethoxy-7-azanorbomadiene (2) in 90% yield. The uncatalyzed reaction gives yields of 35-40%. The improved yield is attributed to the milder reaction conditions and the fact that formation of a complex of (2) with AICI , renders the reaction irreversible. The reaction is the first step in an im-... 

DIELS-ALDER CATALYSTS Aluminum chloride. Boron trifluoride etherate. 

DIELS-ALDER CATALYSTS Aluminum chloride. Boron trifluoiide etherate. DIELS-ALDER REACTIONS 2,3-Bis-(trimethylsilyloxy)-l,3-butadiene. 

Aluminum chloride, 60, 61 Diels-Alder catalyst, 144 Friedel-Crafts acylation catalyst, 91-100 MA complex, 212 Aluminum, diethyl chloride, 345 Aluminum oxide, dehydrating catalyst, 87 Aluminum phenoxides, MA polymerization reactant, 273... 

Copper chloride, Diels-Alder catalyst, 144 Copper oxides, promoters for MA catalyst, 36 Cotton, poly(styrene-alt-MA) grafted, 476 Cotton fabric, MA condensation, 503 Coumaline see a-pyrone Coumaran see 2,3-benzofuran Coumarin, 100... 

Phthaloyl chloride, reaction with MA, 101 a-Picoline, MA polymerization initiator, 256 -Picoline, MA polymerization initiator, 256 7-Picoline, MA polymerization, 256 Picric acid, Diels-Alder catalyst, 119 a-Pinene... 

The Diels-Alder reaction was thought for many years to be only slightly influenced by catalysts. However, in 1960, Yates and Eaton (6) clearly demonstrated that with certain dienophiles, the presence of a molar equivalent of aluminum chloride can cause a remarkable acceleration of the reaction. Providing the diene is not polymerized (7) or otherwise destroyed by the catalyst, the modification can be fruitfully employed to carry out the reaction at lower temperature and for shorter times. 

The discovery that Lewis acids can promote Diels-Alder reactions has become a powerful tool in synthetic organic chemistry. Yates and Eaton [4] first reported the remarkable acceleration of the reactions of anthracene with maleic anhydride, 1,4-benzoquinone and dimethyl fumarate catalyzed by aluminum chloride. The presence of the Lewis-acid catalyst allows the cycloadditions to be carried out under mild conditions, reactions with low reactive dienes and dienophiles are made possible, and the stereoselectivity, regioselectivity and site selectivity of the cycloaddition reaction can be modified [5]. Consequently, increasing attention has been given to these catalysts in order to develop new regio- and stereoselective synthetic routes based on the Diels-Alder reaction. 

Chloroaluminate ionic liquids (typically a mixture of a quaternary ammonium salt with aluminum chloride see Table 6.9) exhibit at room temperature variable Lewis acidity and have been successfully used as solvent/catalyst for Diels-Alder reactions [57]. The composition of chloroaluminate ionic liquids can vary from basic ([FMIM]C1 or [BP]C1 in excess) to acidic (AICI3 in excess) and this fact can be used to affect the reactivity and selectivity of the reaction. The reaction of cyclopentadiene with methyl acrylate is an example (Scheme 6.31). 

Ruthenium complexes have also been reported as active species for enan-tioselective Diels-Alder reactions. Faller et al. prepared a catalyst by treatment of (-)-[( ] -cymene)RuCl(L)]SbF6 with AgSbFe resulting in the formation of a dication by chloride abstraction [95]. The ligand was (-l-)-IndaBOx 69 (Scheme 36) and the corresponding complex allowed the condensation of methacrolein with cyclopentadiene in 95% conversion and 91% ee. As another example, Davies [96] prepared the complex [Ru(Fl20)L ( i -mes)] [SbFe]2 (with 70 as L in Scheme 36), and tested its activity in the same reaction leading to the expected product with similar activity and lower enan-tioselectivity (70%). 

Cycloaddition of 2-cyanoalk-2-enones with several conjugated dienes proceeded under zinc chloride catalysis.636 Zinc halides have also shown reactivity with phenylacetylenes.637 Zinc chloride is an effective Lewis acid catalyst in the Diels Alder reactions of the keto esters and the effects on stereochemistry of catalysts used have been examined.638... 

Similar to gold(III) chloride, Diels-Alder cycloaddition can also be catalyzed by indium trifluoromethansulfonate. As can be seen below, the reaction proceeds when the mixture is irradiated with microwave. Although the same reaction could take place on standing for several days, the present one is solvent free and the yield is high. Also, the catalyst can be recovered and reused <00TL8639>. 

See also Acetoacetyl-CoA in citric acid cycle, 6 633 Acetyl cyclohexanesulfonyl peroxide (ACSP), 74 282 78 478 Acetylene(s), 7 177-227, 227-228 25 633 addition of hydrogen chloride to, 73 821 from calcium carbide, 4 532, 548 carbometalation of, 25 117 as catalyst poison, 5 257t chemicals derived from, 7 227-265 decomposition of, 70 614 Diels-Alder adduct from cyclopentadiene, 8 222t direct polymerization, 7 514 economic aspects of, 7 216-217 explosive behavior of, 7 181-187 as fuel, 7 221-222 health and safety factors related to, 7 219... 

In 1990, Choudary [139] reported that titanium-pillared montmorillonites modified with tartrates are very selective solid catalysts for the Sharpless epoxidation, as well as for the oxidation of aromatic sulfides [140], Unfortunately, this research has not been reproduced by other authors. Therefore, a more classical strategy to modify different metal oxides with histidine was used by Moriguchi et al. [141], The catalyst showed a modest e.s. for the solvolysis of activated amino acid esters. Starting from these discoveries, Morihara et al. [142] created in 1993 the so-called molecular footprints on the surface of an Al-doped silica gel using an amino acid derivative as chiral template molecule. After removal of the template, the catalyst showed low but significant e.s. for the hydrolysis of a structurally related anhydride. On the same fines, Cativiela and coworkers [143] treated silica or alumina with diethylaluminum chloride and menthol. The resulting modified material catalyzed Diels-Alder reaction between cyclopentadiene and methacrolein with modest e.s. (30% e.e.). As mentioned in the Introduction, all these catalysts are not yet practically important but rather they demonstrate that amorphous metal oxides can be modified successfully. 

The Lewis acid catalyzed reaction of furan (169) with ketovinylphosphonate 170 produced a mixture of adducts, both of which slowly underwent retro Diels-Alder reactions at room temperature121. When diethylaluminum chloride was used as the catalyst, the endo selectivity (with respect to the keto functionality) was enhanced from 171/172 = 58/42 to 78/22 by raising the reaction temperature from — 25 °C to 0°C (equation 47). This is in agreement with the FMO theory, since initial Lewis acid complexation is with the phosphonate group. 

Sudo and Saigo153 reported the application of ds-2-amino-3,3-dimethyl-l-indanol derived l,3-oxazolidin-2-one 231 as a chiral auxiliary in asymmetric Diels-Alder reactions. The TV-crotonyl and TV-acryloyl derivatives were reacted with cyclopentadiene, 1,3-cyclohexadiene, isoprene and 2,3-dimethyl-l,3-butadiene, using diethylaluminum chloride as the Lewis acid catalyst. The reactions afforded the expected cycloadducts in moderate to high yields (33-97%) with high endo selectivities and high de values (92% to >98%). 

Carbohydrates have found widespread use as chiral auxiliaries in asymmetric Diels-Al-der reactions156. A recent example is a study conducted by Ferreira and colleagues157 who used carbohydrate based chiral auxiliaries in the Lewis acid catalyzed Diels-Alder reactions of their acrylate esters 235 with cyclopentadiene (equation 66). Some representative results of their findings, including the ratios of products 236 and 237, have been summarized in Table 9. The formation of 236 as the main product when diethylaluminum chloride was used in dichloromethane (entry 3) was considered to be the result of an equilibrium between a bidentate and monodentate catalyst-dienophile complex. The bidentate complex would, upon attack by the diene, lead to 236, whereas the monodentate complex would afford 236 and 237 in approximately equal amounts. The reversal of selectivity on changing the solvent from dichloromethane to toluene (entry 2 vs 3) remained unexplained by the authors. 

Cadogan and coworkers160 developed a fructose-derived l,3-oxazin-2-one chiral auxiliary which they applied in the Diels-Alder reactions of its iV-enoyl derivatives 246 with cyclopentadiene using diethylaluminum chloride as the Lewis acid catalyst. The reactions afforded mixtures of endo 247 and exo 248 (equation 68). The catalyst binds to the chiral dienophile in a bidentate fashion (co-ordination to both carbonyl groups). As a consequence, the dienophile is constrained to a rigid conformation which accounts for the almost complete diastereofacial selectivities observed. 

Taguchi and coworkers175 studied the Lewis acid catalyzed asymmetric Diels-Alder reactions of chiral 2-fluoroacrylic acid derivatives with isoprene and cyclopentadiene. When a chiral l,3-oxazolidin-2-one and diethylaluminum chloride were used as the chiral auxiliary and the Lewis acid catalyst, respectively, a de of 90% was observed for the reaction with isoprene. The reaction with cyclopentadiene afforded a 1 1 mixture of endo and exo isomers with de values of 95% and 96%, respectively. The endo/exo selectivity was improved by using 8-phenylmenthol as the chiral auxiliary. Thus, the reaction... 

The reverse reaction is catalysed by copper sulphate in an ethanol/water (50 50) mixture297 298. Indium(III) chloride catalysis of Diels-Alder reactions was also reported, but the effects were poor and comparison to uncatalysed reactions was made only in a few cases299,300. A very versatile Lewis acid catalyst for such reactions is methylrhenium trioxide (MTO)300. This catalyst can be used without a solvent, in pure organic solvents like chloroform and even in pure water. While the catalyst is active in the latter two solvents (Table 22), it gives the best results in water (Table 23). 

Lewis acids such as zinc chloride, boron trifluoride, aluminum chloride, and diethylaluminum chloride catalyze Diels-Alder reactions.8 The catalytic effect is the result of coordination of the Lewis acid with the dienophile. The complexed dienophile is more electrophilic and more reactive toward electron-rich dienes. The mechanism of the cycloaddition is still believed to be concerted, and high stereoselectivity is observed.9 10 Lewis acid catalysts also usually increase the regioselectivity of the reaction. 

Metal complexes of bis(oxazoline) ligands are excellent catalysts for the enantioselective Diels-Alder reaction of cyclopentadiene and 3-acryloyl-l,3-oxa-zolidin-2-one. This reaction was most commonly utilized for initial investigation of the catalytic system. The selectivity in this reaction can be twofold. Approach of the dienophile (in this case, 3-acryloyl-l,3-oxazolidin-2-one) can be from the endo or exo face and the orientation of the oxazolidinone ring can lead to formation of either enantiomer R or S) on each face. The ideal catalyst would offer control over both of these factors leading to reaction at exclusively one face (endo or exo) and yielding exclusively one enantiomer. Corey and co-workers first experimented with the use of bis(oxazoline)-metal complexes as catalysts in the Diels-Alder reaction between cyclopentadiene 68 and 3-acryloyl-l,3-oxazolidin-2-one 69 the results are summarized in Table 9.7 (Fig. 9.20). For this reaction, 10 mol% of various iron(III)-phe-box 6 complexes were utilized at a reaction temperature of —50 °C for 2-15 h. The yields of cycloadducts were 85%. The best selectivities were observed when iron(III) chloride was used as the metal source and the reaction was stirred at —50 °C for 15 h. Under these conditions the facial selectivity was determined to be 99 1 (endo/exo) with an endo ee of 84%. 

Imines, ethyl acetylenedicarboxylate and benzoyl chloride were combined in the presence of carbon monoxide and a palladium-tri-o-tolylphosphine catalyst system to pyrrole derivatives (3.90.). Although the carbon monoxide is formally oxidized to carbon dioxide, during the catalytic cycle it is inserted into the intermediates formed and is extruded in a retro-Diels-Alder reaction only in the concluding step of the reaction sequence.114... 

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