Catalyzed Diels-Alder Reaction Research Articles

Asymmetric Organocatalytic Transfer Hydrogenation of Cyclic Enones

The authors describe a highly enantioselective organocatalytic transfer hydro­genation of cyclic α,β-unsaturated ketones 1. The reaction is mediated by imidazolidinone catalyst 3, which has previously been used in iminium catalytic Diels-Alder reactions of α,β-unsaturated ketones with dienes. Valuable chiral cyclic ketones 4 are obtained in moderate to good yields and good to excellent enantioselectivities in the presence of tert-butyl Hantzsch ester 2 as hydrogen source. This process was successfully applied to five-, six-, and seven-membered ring systems.

An examination of VANOL, VAPOL, and VAPOL derivatives as ligands for asymmetric catalytic Diels–Alder reactions

Several derivatives of the vaulted biaryl ligand VAPOL were prepared and evaluated as chiral ligands for aluminum Lewis acids in the catalytic asymmetric Diels–Alder reactions of methyl acrylate and methacrolein with cyclopentadiene. The substituents on VAPOL were introduced into the 6- and 6′-positions in an effort to further extend the chiral pocket of the major groove, which contains the phenol functions at the 4- and 4′-positions. The set of four new ligands that have been prepared have the following groups introduced into the 6- and 6′-positions of VAPOL: bromide, methyl, phenyl and 3,5-di-t-butylphenyl. All of these ligands give lower asymmetric inductions than the unsubstituted VAPOL for the Diels–Alder reactions of both methyl acrylate and methacrolein. The positive cooperativity of added carbonyl compounds on the autoinduction in the Diels–Alder reaction of methyl acrylate and cyclopentadiene were also investigated with the VANOL and VAPOL ligands as well as the 6,6′-dibromo and 6,6′-diphenyl derivatives of VAPOL. Only the reaction with VAPOL showed any significant positive cooperativity. The reaction with VANOL was sluggish at –78 °C, but at higher temperatures, the reaction did exhibit positive cooperativity that was similar to that of VAPOL. Finally, no positive cooperativity was observed with the VAPOL ligand for the reaction of methacrolein and cyclopentadiene.Key words: Diels–Alder, asymmetric catalysis, vaulted biaryl ligands, VANOL, VAPOL.

Asymmetric Cobalt-Catalyzed Diels−Alder Reactions of a Boron-Functionalized 1,3-Diene with Alkynes and Allylboration with Aldehydes

[Structure: see text] A cobalt(I)-catalyzed Diels-Alder reaction of a 1-boron-functionalized 1,3-diene is the key step in a one-pot reaction interconnecting three simple starting materials to obtain a multifunctionalized product. This product incorporates a stereogenic quaternary center next to a stereogenic secondary alcohol functionality generated with a very high degree of regio- and diastereoselectivity and good enantioselectivity in the presence of a chiral ligand such as (S,S)-Norphos.

Highly Enantioselective DNA‐Based Catalysis.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Highly enantioselective DNA-based catalysis

A new approach to DNA-based asymmetric catalysis is presented, which gives rise to very high enantioselectivities (up to 99% ee) in the copper catalyzed Diels-Alder reaction in water.

Enantioselective Diels-Alder Route to Isoquinuclidines

An enantioselective catalytic Diels-Alder reaction to isoquinuclidines using a chiral palladium catalyst is reported. Thus, the reaction of a N-protected 1,2-dihydropyridine with acryloyl-1,3-oxazolidine-3-one proceeds under 10 mol% Pd-POZ catalysis in up to 98% yield and with 88% ee. Using 1-benzyl-2-aroylpyrazolidin-3-ones as dienophiles, 87% yield and 97% ee were achieved. Of the several counterions for the Pd-POZ catalyst which were tested, SbF6 - gave the highest ee’s. Other investigated catalysts, such as Cu-bis(oxazoline), Pd-BINAP or other Pd-POZs gave poorer results.

Silica Gel‐Supported Cation Radical Catalyzed Diels—Alder Reaction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Dihydroaromatic Boronic Esters as Building Blocks for the Synthesis of Phenanthrenes and Phenanthridines.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Silica Gel-Supported Cation Radical Catalyzed Diels-Alder Reaction

The discovery of the cation-radical catalyzed Diels-Alder reaction opened a field of cation radical chemistry. The inefficiency of reactions involving neutral or electron-rich dienophiles imposes a major constraint on the Diels-Alder reaction. This reactivity constraint might be relieved by using cation radical which converts these dienophiles to their corresponding electron-deficient species. Bauld has reported that tris(p-bromophenyl) aminium hexachloroantimonate 1 was efficient for certain Diels-Alder reactions. The successful development of homogeneous catalysts has been often followed by attempts to attach them onto an insoluble polymeric support. The attachment of homogeneous catalysts to an insoluble support gives advantages over traditional solution phase chemistry. The immobilized catalysts can be separated from reaction mixture by simple filtration and then is easily regenerated for reuse. The method would be attractive from an economical viewpoint as well as a simplified work-up. Our interest in the area led us to prepare a silica gel-supported aminium cation radical. Herein, we describe the synthesis of silica gel-supported triphenylamine cation radical 2 and its application in DielsAlder reaction. As shown in Scheme 1, we prepared triphenylamine monomer 6 containing a reactive vinyl group which can be immobilized on a modified silica gel. The Friedel-Crafts reaction of triphenylamine with acetyl chloride provided 3 in 70% yield. Treatment of 3 with NBS gave 4 in 81% yield. Reduction of 4 with lithium aluminum hydride afforded 5 in 91% yield. Attempts to drive the next step to 6 by treatment of 5 with conventional dehydrating reagents such as H2SO4, KHSO4, Al2O3 and POCl3/pyridine failed due to too low yield. In the case of TsCl/t-BuOK, the formation of the

Dihydroaromatic Boronic Esters as Building Blocks for the Synthesis of Phenanthrenes and Phenanthridines

AbstractAlkenyl‐substituted dihydroaromatic boronic esters, generated by neutral cobalt(I)‐catalysed Diels–Alder reactions, reacted under palladium catalysis conditions with diiodobenzene, bromoiodobenzene and iodoaniline derivatives for the synthesis of regioselectively substituted phenanthrene and phenanthridine derivatives. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The synthesis and catalytic application of spacer-modified diol-functionalised Merrifield resins

A range of alkyl spacer-tethered 1,2- and 1,3-diols have been prepared from commercially available Merrifield resin ( 1 ) and (4-chloromethyl)phenylpentyl-polystyrene-co-divinylbenzene ( 2 ). The utility of these resin-bound diols as supports for the Ti(IV)-catalysed Diels–Alder reaction has been exemplified and it has been demonstrated that the length of the tether has a direct effect upon the catalytic activity.

Small-Molecule Diversity Using a Skeletal Transformation Strategy

[reaction: see text] We describe a short synthetic sequence resulting in >4000 skeletally diverse small molecules that have three distinct skeletal frameworks among other unique structural features. The sequence entails skeletal transformations pioneered by Winterfeldt and co-workers. We use epoxide ring openings and subsequent functionalizations that provide, e.g., spirocyclic oxazolidines, Lewis acid catalyzed Diels-Alder reactions of a steroid-derived diene that afford stable and isolable ring B adducts, and subsequent retro-Diels-Alder fragmentations that yield 14-membered paracyclophanes.

Photochemically Catalyzed Diels—Alder Reaction of Arylimines with N‐Vinylpyrrolidinone and N‐Vinylcarbazole by 2,4,6‐Triphenylpyrylium Salt: Synthesis of 4‐Heterocycle‐Substituted Tetrahydroquinoline Derivatives.

Abstract Photochemically promoted Diels–Alder reactions of N-arylimines with N-vinylpyrrolidinone and N-vinylcarbazole were achieved by using 2,4,6-triphenylpyrylium tetrafluoroborate as a catalyst to produce corresponding 2-oxopyrrolidin-1-yl and carbazol-9-yltetrahydroquinolines in high yields.

Recyclable Organotungsten Lewis Acid and Microwave‐Assisted Diels—Alder Reactions in Water and in Ionic Liquids.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The modulation of face–face π–π interactions in Lewis acid catalysis

The enantiomeric excess observed for the exo-adduct from the Lewis acid catalysed Diels–Alder reaction between cyclopentadiene and methacrolein can be increased up to 21% by simple modification of the electronics of the aromatic ring in a series of stilbene-derived diol ligands, suggesting that the proposed face–face π–π interaction between the catalyst and the dienophile can be modulated by altering the electron density on the aromatic ring.

Cobalt(I)-Catalysed Neutral Diels-Alder Reactions of Nitrogen-Functionalised Alkynes

Imide, sulfimide and amide type protection of nitrogen-functionalised alkynes proofed to be effective protective groups tolerated in cobalt(I)-catalysed Diels-Alder reactions of 1,3-dienes.

A Two-Step Reaction Sequence for the Syntheses of Tetrahydronaphthalenes

[Reaction: see text] A cobalt(I)-catalyzed Diels-Alder reaction of a boron-functionalized enyne is the key step in a two-step reaction cascade interconnecting four simple starting materials to obtain polycyclic multifunctionalized products in good yields and with a very high degree of diastereoselectivity.

Photochemically catalyzed Diels–Alder reaction of arylimines with N-vinylpyrrolidinone and N-vinylcarbazole by 2,4,6-triphenylpyrylium salt: synthesis of 4-heterocycle-substituted tetrahydroquinoline derivatives

Photochemically promoted Diels–Alder reactions of N-arylimines with N-vinylpyrrolidinone and N-vinylcarbazole were achieved by using 2,4,6-triphenylpyrylium tetrafluoroborate as a catalyst to produce corresponding 2-oxopyrrolidin-1-yl and carbazol-9-yltetrahydroquinolines in high yields.

Photochemically Catalyzed Diels—Alder Reaction of N‐Arylimines by 2,4,6‐Triphenylpyrylium Salt: Synthesis of Furo‐ and Pyranoquinoline Derivatives.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Recyclable organotungsten Lewis acid and microwave assisted Diels–Alder reactions in water and in ionic liquids

The water-soluble, organotungsten Lewis acid, [O P(2-py) 3W(CO)(NO) 2](BF 4) 2 ( 1 ), was synthesized and characterized. A series of 1 -catalyzed Diels–Alder reactions were investigated under conventional heating or microwave heating conditions. The cycloaddition reactions were efficiently conducted in either water or in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate. The ionic liquid acts as a powerful medium not only for rate- and selectivity enhancements but also for facilitating catalyst recycling. Dramatic rate acceleration via microwave flash heating as compared to thermal heating was observed.