5257-46-5Relevant articles and documents
CATALYSIS OF DIELS-ALDER REACTIONS BY METALLOPORPHYRINS
Bartley, David W.,Kodadek, Thomas J.
, p. 6303 - 6306 (1990)
Aluminium (III) tetraphenyl porphyrin chloride (AITPPCl) has been shown to catalyze Diels-Alder reactions of α,β-unsaturated carbonyl compounds in moderate yield.Selectivity based on electronic effects is exhibited which is different from that seen with catalysts such as diethylaluminium chloride.
Bis-selenonium Cations as Bidentate Chalcogen Bond Donors in Catalysis
He, Xinxin,Wang, Xinyan,Tse, Ying-Lung Steve,Ke, Zhihai,Yeung, Ying-Yeung
, p. 12632 - 12642 (2021/10/21)
Lewis acids are frequently employed in catalysis but they often suffer from high moisture sensitivity. In many reactions, catalysts are deactivated because of the problem that strong Lewis acids also bond to the products. In this research, hydrolytically stable bidentate Lewis acid catalysts derived from selenonium dicationic centers have been developed. The bis-selenonium catalysts are employed in the activation of imine and carbonyl groups in various transformations with good yields and selectivity. Lewis acidity of the bis-selenonium salts was found to be stronger than that of the monoselenonium systems, attributed to the synergistic effect of the two cationic selenonium centers. In addition, the bis-selenonium catalysts are not inhibited by strong bases or moisture.
Chiral protic imidazolium salts with a (-)-menthol fragment in the cation: Synthesis, properties and use in the Diels-Alder reaction
Janus, Ewa,Gano, Marcin,Feder-Kubis, Joanna,So?nicki, Jacek
, p. 10318 - 10331 (2018/03/26)
New chiral protic imidazolium salts containing a (1R,2S,5R)-(-)-menthol substituent in the cation and four different anions (chloride, hexafluorophosphate, trifluoromethanesulfonate and bis(trifluoromethylsulfonyl)imide) were efficiently prepared and exte
Ruthenium Lewis Acid-Catalyzed Asymmetric Diels–Alder Reactions: Reverse-Face Selectivity for α,β-Unsaturated Aldehydes and Ketones
Thamapipol, Sirinporn,Ludwig, Bettina,Besnard, Céline,Saudan, Christophe,Kündig, E. Peter
, p. 774 - 789 (2016/10/17)
Acrolein, methacrolein, methyl vinyl ketone, ethyl vinyl ketone, 3-methyl-3-en-2-one, and divinyl ketone were coordinated to a cationic cyclopentadienyl ruthenium(II) Lewis acid incorporating the electron-poor bidentate BIPHOP–F ligand. Analysis by NOESY and ROESY NMR techniques allowed the determination of conformations of enals and enones present in solution in CD2Cl2. The results were compared to solid-state structures and to the facial selectivities of catalytic asymmetric Diels–Alder reactions with cyclopentadiene. X-Ray structures of four Ru-enal and Ru-enone complexes show the α,β-unsaturated C=O compounds to adopt an anti-s-trans conformation. In solution, enals assume both anti-s-trans and anti-s-cis conformations. An additional conformation, syn-s-trans, is present in enone complexes. Enantioface selectivity in the cycloaddition reactions differs for enals and enones. Reaction products indicate enals to react exclusively in the anti-s-trans conformation, whereas with enones, the major product results from the syn-s-trans conformation. The alkene in s-cis conformations, while present in solution, is shielded and cannot undergo cycloaddition. A syn-s-trans conformation is found in the solid state of the bulky 6,6-dimethyl cyclohexanone-Ru(II) complex. The X-ray structure of divinyl ketone is unique in that the Ru(II) center binds the enone via a η2bond to one of the alkene moieties. In solution, coordination to Ru–C=O oxygen is adopted. A comparison of facial preference is also made to the corresponding indenyl Lewis acids.
Silylium ion-catalyzed challenging Diels-Alder reactions: The danger of hidden proton catalysis with strong Lewis acids
Schmidt, Ruth K.,Muether, Kristine,Mueck-Lichtenfeld, Christian,Grimme, Stefan,Oestreich, Martin
supporting information; experimental part, p. 4421 - 4428 (2012/04/23)
The pronounced Lewis acidity of tricoordinate silicon cations brings about unusual reactivity in Lewis acid catalysis. The downside of catalysis with strong Lewis acids is, though, that these do have the potential to mediate the formation of protons by various mechanisms, and the thus released Bronsted acid might even outcompete the Lewis acid as the true catalyst. That is an often ignored point. One way of eliminating a hidden proton-catalyzed pathway is to add a proton scavenger. The low-temperature Diels-Alder reactions catalyzed by our ferrocene-stabilized silicon cation are such a case where the possibility of proton catalysis must be meticulously examined. Addition of the common hindered base 2,6-di-tert-butylpyridine resulted, however, in slow decomposition along with formation of the corresponding pyridinium ion. Quantitative deprotonation of the silicon cation was observed with more basic (Mes)3P to yield the phosphonium ion. A deuterium-labeling experiment verified that the proton is abstracted from the ferrocene backbone. A reasonable mechanism of the proton formation is proposed on the basis of quantum-chemical calculations. This is, admittedly, a particular case but suggests that the use of proton scavengers must be carefully scrutinized, as proton formation might be provoked rather than prevented. Proton-catalyzed Diels-Alder reactions are not well-documented in the literature, and a representative survey employing TfOH is included here. The outcome of these catalyses is compared with our silylium ion-catalyzed Diels-Alder reactions, thereby clearly corroborating that hidden Bronsted acid catalysis is not operating with our Lewis acid. Several simple-looking but challenging Diels-Alder reactions with exceptionally rare dienophile/enophile combinations are reported. Another indication is obtained from the chemoselectivity of the catalyses. The silylium ion-catalyzed Diels-Alder reaction is general with regard to the oxidation level of the α,β-unsaturated dienophile (carbonyl and carboxyl), whereas proton catalysis is limited to carbonyl compounds.
Triethylsulfonium bistriflimide as the reaction medium in catalyzed and uncatalyzed cycloaddition [4 + 2]
Janus, Ewa,Bittner, Bozena
experimental part, p. 147 - 154 (2010/11/05)
Triethylsulfonium bistriflimide, [S2.2.2][NTf2], has been tested and compared with other ionic liquids and molecular solvents as a medium in Diels-Alder reaction between cyclopentadiene and dimethyl maleate. Triflates and chlorides of different metals have been combined with [S 2.2.2][NTf2] and the catalytic activity of the systems formed have been determined. The effect of concentration of the catalysts in sulfonium ionic liquid and reactants on the yield and endo:exo ratio has been established. The representative catalyst-Yb(OTf)3?xH 2O in [S2.2.2][NTf2] has been examined in the reaction of cyclopentadiene with various dienophiles. The use of sulfonium ionic liquids permitted recycling the catalysts. For the best four catalytic systems, the products have been isolated.
Enhanced Diels-Alder reactions: on the role of mineral catalysts and microwave irradiation in ionic liquids as recyclable media
López, Ignacio,Silvero, Guadalupe,Arévalo, María José,Babiano, Reyes,Palacios, Juan?Carlos,Bravo, José Luis
, p. 2901 - 2906 (2007/10/03)
This manuscript explores in detail the combined effect of solid supports or microwave irradiation in ionic liquids on a series of Diels-Alder reactions involving 1,3-cyclopentadiene and numerous dienophiles.
Reversal of chemoselectivity in diels-alder reaction with α,β-unsaturated aldehydes and ketones catalyzed by bronsted acid or Lewis Acid
Nakashima, Daisuke,Yamamoto, Hisashi
, p. 1251 - 1253 (2007/10/03)
(Chemical Equation Presented) High chemoselectivity was observed in the Diels-Alder reaction of α,β-unsaturated aldehyde and α,β-unsaturated ketone with cyclopentadiene. Using Tf2NH as catalyst, the reaction gave Diels-Alder adduct derived from α,β-unsaturated ketone as a major product. On the other hand, bulky Lewis acid, B(C6F5)3, gave mainly the cycloadduct of α,β-unsaturated aldehyde and cyclopentadiene.
An in-depth look at the effect of Lewis acid catalysts on Diels-Alder cycloadditions in ionic liquids
Silvero, Guadalupe,Arévalo, María José,Bravo, José Luis,ávalos, Martín,Jiménez, José Luis,López, Ignacio
, p. 7105 - 7111 (2007/10/03)
The present work explores in detail the Diels-Alder reaction between cyclopentadiene and a series of dienophiles, performed in an innovative medium such as an ionic liquid. The potential activation of different Lewis acid catalysts and their load effect when used in combination with this solvent have been explored, in order to settle the improvement on rates and selectivities.
I2 as an efficient catalyst in ionic Diels-Alder reactions of α,β-unsaturated acetals
Chavan, Subhash P.,Sharma, Pallavi,Rama Krishna,Thakkar, Mahesh
, p. 3001 - 3003 (2007/10/03)
A variety of protected and unprotected α,β-unsaturated aldehydes react with 1,3-dienes in the presence of I2 to give the corresponding cycloadducts.
