Catalyzed Diels-Alder Reaction Research Articles

The First Broad Application of Alkynyl Sulfides as Dienophiles in Cobalt(I)‐Catalyzed Diels—Alder Reactions.

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Photochemically Catalysed Diels–Alder Reaction of N-arylimines by 2,4, 6-triphenylpyrylium Salt: Synthesis of Furo- and Pyranoquinoline Derivatives

Photochemically promoted Diels–Alder reactions of N-arylimines with 2,3-dihydrofuran and 3,4-dihydro-2 H-pyran were achieved by using 2,4,6-triphenylpyrylium tetrafluoroborate as a catalyst to produce the corresponding furo- and pyranoquinolines in high yield.

Glyoxal Bis‐hydrazones: A New Family of Nitrogen Ligands for Asymmetric Catalysis.

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Asymmetric Lewis Acid Catalyzed Diels—Alder Reactions of α,β‐Unsaturated Ketones and α,β‐Unsaturated Acid Chlorides.

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The first broad application of alkynyl sulfides as dienophiles in cobalt(I)-catalyzed Diels-Alder reactions.

The cobalt(I)-catalyzed Diels-Alder reaction of nonactivated aryl alkynyl sulfides with acyclic 1,3-dienes generates dihydroaromatic vinyl sulfides under very mild reaction conditions, and these products can be oxidized with mild oxidants to the corresponding diaryl sulfides in good overall yields. The steric and electronic effects of substituents on the aryl, as well as on the alkynyl, moieties of the aryl alkynyl sulfide are discussed. While the cobalt catalyst system is quite efficient in converting alkynyl sulfides to the Diels-Alder adducts, the transformation of the corresponding aryl alkynyl sulfoxides and sulfones under similar mild reaction conditions gave only moderate yields of the desired adducts.

Glyoxal bis-hydrazones: a new family of nitrogen ligands for asymmetric catalysis.

The introduction of C2-symmetric dialkylamino substructures in chiral non-racemic glyoxal bis-hydrazones such as 9 appears as the key design element for this novel ligand class, as shown in the highly enantioselective copper(II)-catalyzed Diels–Alder reaction.

Stereoselective synthesis using immobilized Diels-Alderase ribozymes.

Development of artificial ribozymes by in vitro selection has so far, mostly been addressed from the viewpoint of fundamental research. However, such ribozymes also have high potential as selective catalysts in practical syntheses. Immobilization of an active and selective ribozyme is an important step towards this end. A 49-nucleotide RNA molecule that was previously found to stereoselectively catalyze Diels-Alder reactions between various anthracene dienes and maleimide dienophiles was quantitatively immobilized on an agarose matrix by periodate oxidation of the 3'-terminal ribose and coupling to a hydrazide moiety. Typical loadings were 45 pmol microL(-1) gel. The specific activity was comparable to that of soluble ribozyme, and high enantioselectivities were obtained in catalyzed cycloadditions. The catalytic matrix was found to be stable and could be regenerated about 40 times with only minimal reduction of catalytic activity. Like the soluble ribozyme, the immobilized catalyst stereoselectively converts various diene and dienophile substrates. By using either natural D-RNA or enantiomeric L-RNA, both product enantiomers were made synthetically accessible with similar selectivities.

Planar Chiral PHANOLs as Organocatalysts for the Diels—Alder Reaction via Double Hydrogen‐Bonding to a Carbonyl Group.

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Molecular Signal Transduction by Conformational Transmission

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The Preparation and Utility of Bis(sulfinyl)imidoamidine Ligands for the Copper‐Catalyzed Diels—Alder Reaction.

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The Influence of Ligand Side Chain on the Enantioselectivity of Lewis Acid Catalyzed Diels—Alder Reactions.

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The effect of solvent on a Lewis acid catalyzed Diels-Alder reaction, using computed and experimental kinetic isotope effects.

A new transition structure for the Diels-Alder reaction between isoprene and acrolein catalyzed by Et(2)AlCl is found to reconcile reported discrepancies between computed and observed secondary kinetic isotope effects (KIEs). Including the effect of solvent realigns the computed results with experiment demonstrating the importance of nonbond interactions at transition structures. Comparison of experimental and newly predicted KIE data reaffirms the ability of theory and experiment to probe the mechanism and transition structure geometry of organic reactions.

Stereocontrolled photo-reaction pathways of endo/exo-2-benzoyl-substituted bicyclo[2.2.2]oct-5-en-2-ol: Paternò–Büchi reaction versusα-cleavage

Two stereoisomeric ketones, endo- and exo-(2-hydroxy-[2.2.2]bicyclo-5-en-1-yl)-phenyl methanone (endo-2 and exo-2) were synthesized via a Lewis acid catalyzed Diels–Alder reaction. Both compounds were tested in terms of their efficiency as photoinitiators for radical polymerization. Whereas the exo isomer serves as a good photoinitiator, the curing efficiency is poor in the case of the endo derivative. CIDNP investigations and product analysis by NMR and GC-MS together with density functional calculations reveal the distinctly different reaction pathways of the two isomers. On one hand, exo-2 undergoes α-cleavage from the triplet excited state forming a radical pair that is able to induce polymerizations. On the other hand, endo-2 cyclizes in a Paternò–Büchi reaction yielding a tetracyclic product 11 and no formation of radicals is observed.

10 Reaction mechanisms : Part (iii) Pericyclic reactions

Computational studies of pericyclic reaction mechanisms have greatly enhanced our understanding of, and predictions regarding, reaction mechanisms. In recent years, the importance of non-statistical effects in pericyclic reactions, as studied using dynamics trajectory calculations, has been recognized. Some examples are the electrocyclic ring opening of the cyclopropyl radical, the Cope rearrangement of hepta-1,2,6-triene, and the rearrangement of bicyclo[n.1.0]polyenes. High quality mechanistic studies, though becoming less common, were also carried out. For example, two studies were published on vinylcyclobutane derivatives, one focusing on the thermal stereomutations and cycloreversions, and the other on the [1,3] sigmatropic reactions. The strength of the interplay between experiment and theory is demonstrated in studies of the intramolecular [4+2] cycloaddition of cyclobutadiene with tethered alkenes, in the use of isotope effects to determine the mechanism of an electron-transfer catalyzed Diels–Alder reaction, and in the degenerate interconversions of bicyclo[3.1.0]hex-2-ene.

Planar Chiral PHANOLs as Organocatalystsfor the Diels-Alder Reaction via Double Hydrogen-Bondingto a Carbonyl Group

Planar chiral PHANOLs have been shown to catalyze Diels-Alder reactions of a,b-unsaturated aldehydes and ketones with various dienes. Rate accelerations of up to ca. 30-fold were obtained using the electron deficient 4,12-dihydroxy-7,15-dinitro[2.2]paracyclophane as a catalyst. It is proposed that the carbonyl group of the dienophile is activated via a double hydrogen-bonding mode. Although the PHANOLs are inherently chiral, little or no asymmetric induction was observed when using enantiopure (R)-PHANOL.

Molecular Signal Transductionby Conformational Transmission

2,3,6,7-Tetrasubstituted cis-anti-cis perhydroanthracenes and cis-decalines are suitable transducers for molecular signals via conformational transmission. Repeated use of a Lewis-acid catalyzed Diels-Alder reaction led to the stereoselective construction of the perhydroanthracene and decalin target molecules. A covalently induced triple ring flip of the perhydroanthacene system was achieved by the formation of a bisacetal. A chelation induced conformational switch was possible with bipyridine receptor groups in positions 6 and 7 and Zn(II) as the incoming signal. By attaching pyrene effectors in positions 2 and 3 the ability of the device to transduce a molecular signal from the receptor via the biconformational transducer to the effector leading to an outcoming photosignal was proven.

Efficient synthesis of a tricyclic BCD analogue of ouabain: Lewis acid catalyzed Diels-Alder reactions of sterically hindered systems.

Efficient synthesis of a tricyclic BCD analogue of ouabain: Lewis acid catalyzed Diels-Alder reactions of sterically hindered systems.

The preparation and utility of bis(sulfinyl)imidoamidine ligands for the copper-catalyzed Diels-Alder reaction.

The design and preparation of a novel class of ligands based on the sulfinyl imine functionality is described. In particular, an efficient and modular synthesis of bis(sulfinyl)imidoamidine (siam) ligands is reported. The versatility of the synthetic sequence is demonstrated by the preparation of various analogues to explore the effect of substitution about the ligand framework on catalytic activity. The utility of the siam ligands in asymmetric catalysis is demonstrated in the Cu(II)-catalyzed Diels-Alder reaction where highly enantio- and diastereoselective reactions are reported for a range of N-acyloxazolidinone dienophile and diene substrate combinations. Of particular note is the efficiency of these asymmetric catalysts for reactions involving challenging and relatively unreactive acyclic diene substrates. Finally, structural data are provided for several ligands as well as metal-ligand complexes.

ChemInform Abstract: The First General Enantioselective Catalytic Diels—Alder Reaction with Simple α,β‐Unsaturated Ketones.

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Studies on the synthesis of the quartromicins: partial stereochemical assignment of quartromicins A 3 and D 3 and diastereoselective synthesis of the endo- and exo-spirotetronate subunits

A partial stereochemical assignment of quartromicins A 3 and D 3 is presented, along with diastereoselective syntheses of the endo- and exo-spirotetronates 1 and 2 , corresponding to the galacto and agalacto fragments of the proposed quartromicin stereostructure. The key steps of these syntheses are highly enantio- and diastereoselective Lewis acid catalyzed Diels–Alder reactions of 1,1,3,4-tetrasubstituted diene 24 .