Reactive Diene Research Articles

On the role of s-cis conformers in the reaction of dienes with OH radicals

The reactions of OH radicals with s-cis and s-trans-butadiene and s-cis-isoprene have been modeled by ab initio Molecular Orbital Theory. Density Functional Theory (BHandHLYP) calculations have been performed for both butadiene and isoprene, and Moller–Plesset Perturbation Theory to the second-order (MP2) has also been used for s-cis-isoprene in order to compare with previous work. Pre-reactive complexes are identified in all cases, with the OH radical placed over either one of the double bonds at a distance of about 2 A and the H atom pointing towards the C–C bond. The geometries of the transition states corresponding to OH addition at all positions have been fully optimized. The calculated apparent activation energies are negative for addition at the terminal carbon atoms and in excellent agreement with the experimental measurements. The possible role of direct additions at the internal carbon atoms in the formation of furan-like compounds is discussed. Energy barriers for the s-cis conformers are found to be smaller than those for the s-trans conformers, especially for addition at the internal carbons, suggesting that the s-cis conformers could play a role in the tropospheric oxidation of dienes. Calculated overall rate constants are in good agreement with experimental values. Partial rate coefficients corresponding to the different channels are reported. The temperature dependence is studied in the 290–500 K range and two-parameter equations are reported for each rate coefficient. The calculated partial rate coefficients of addition to internal carbon atoms are not large enough to account for the observed yield of 3-methylfuran.

Synthesis of new chiral auxiliaries for 6π-azaelectrocyclization: 4- and 7-alkyl substituted cis-1-amino-2-indanols

The synthesis of new chiral auxiliaries, 7-alkyl substituted cis-1-amino-2-indanol derivatives, was established by the Diels–Alder reaction of 1-substituted dienes with cyclopentenone followed by the asymmetric epoxidation of the resulting indene derivatives and then the Ritter reaction. These bulky cis-aminoindanol derivatives are very effective as chiral auxiliaries and nitrogen sources in the asymmetric 6π-azaelectrocyclization. The corresponding 4-alkyl derivative was also prepared using a similar method.

Assembled dendritic titanium catalysts for enantioselective hetero-Diels-Alder reaction of aldehydes with Danishefsky's diene.

A new type of dendritic 2-amino-2'-hydroxy-1,1'-binaphthyl (NOBIN)-derived Schiff-base ligands have been synthesized and applied to the titanium-catalyzed hetero-Diels-Alder reaction of Danishefsky's diene with aldehydes. These reactions afforded the corresponding 2-substituted 2,3-dihydro-4H-pyran-4-ones in quantitative yields and with excellent enantioselectivities (up to 97.2 % ee). The disposition of the dendritic wedges and the dendron size in the ligands were found to have significant impact on the enantioselectivity of the reaction. The recovered dendritic catalyst could be reused without further addition of the Ti source or a carboxylic acid additive for at least three cycles, retaining similar activity and enantioselectivity. The high stability of this type of assembled dendritic titanium catalyst may be attributed to the stabilization effect of large-sized dendron units in the catalyst molecule. The other important phenomenon observed with this catalyst system is that a higher degree of asymmetric amplification has been achieved by attachment of the dendron unit to the chiral ligand, which represents a new advantage of dendrimer catalysts for asymmetric reactions using chiral ligands of lower optical purity.

Total syntheses of amphidinolide T1, T3, T4, and T5.

A concise, flexible, and high yielding entry into the family of amphidinolide T macrolides, a series of cytotoxic natural products of marine origin, has been developed. All individual members, except amphidinolide T3 (3), derive from compound 39 as a common synthetic intermediate which is formed from three building blocks of similar size and complexity. The fragment coupling steps involve a highly diastereoselective SnCl(4) mediated reaction of the furanosyl sulfone derivative 11 with the silyl enol ether 18 and a palladium-catalyzed Negishi type coupling reaction between the polyfunctional organozinc reagent derived from iodide 32a and the enantiopure acid chloride 24b. The 19-membered macrocyclic ring is then formed by a high yielding ring closing metathesis (RCM) reaction of diene 33 catalyzed by the "second generation" ruthenium carbene complex 34. The efficiency of the RCM transformation stems, to a large extent, from the conformational bias introduced by the syn-syn-configured stereotriad at C12-C14 of the substrate which constitutes a key design element of the synthesis plan. The use of Nysted's reagent 38 in combination with TiCl(4) was required for the olefination of the sterically hindered ketone group in 36, whereas more conventional alkene formations were unsuccessful for this elaboration. Finally, it is shown that the inversion of a single and seemingly remote stereocenter (C12) in one of the building blocks not only affects the efficiency and stereochemical outcome of the RCM step but also exerts a significant influence on the course of the acyl-Negishi reaction, allowing a radical manifold to compete with productive cross coupling.

Asymmetric Diels–Alder reactions in supercritical carbon dioxide catalyzed by rare earth complexes

The rare earth(III) salt catalysed asymmetric Diels–Alder reaction of cyclopentadiene with a chiral dienophile in supercritical carbon dioxide (scCO2) proceeded rapidly to give the adduct with a higher diastereoselectivity than that in dichloromethane; Yb(ClO4)3 gave the endo adduct with value up to 77% de at 40°C, 8 MPa. The chiral rare earth diketonate catalyzed hetero Diels–Alder reaction of the Danishefsky's diene with benzaldehyde gave a higher yield and an enantioselectivity in scCO2 than that in dichloromethane. Scandium/pybox 8a complex catalysed asymmetric Diels–Alder reaction of 3-crotonoyl-2-oxazolidinone with cyclopentadiene in the presence of MS4A proceeded smoothly in scCO2 to give the endo adduct 10 in a good yield with up to 88% ee.

Addition of Carboxyalkyl Radicals to Alkenes Through a Catalytic Process, Using a Mn(II)/Co(II)/O2 Redox System.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthetic studies on macrolactin A by using a (diene)Fe(CO) 3 complex

The stereoselective synthesis of the two segments 3 and 4 of macrolactin A 1 is described. Macrolactin A is a 24-membered polyene macrolide antibiotic, which is of interest due to a strong activity against B16–F10 murine tumor cell and HIV-1 virus. The key step of the synthesis is the 1,2-migration reaction of a (diene)Fe(CO) 3 complex with a introduction of the thiol group to construct the unstable ( E, Z)-conjugated dienic moiety (C8–C11).

An Ionic Liquid Supported Ruthenium Carbene Complex: A Robust and Recyclable Catalyst for Ring‐Closing Olefin Metathesis in Ionic Liquids.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Naphtho[1,2-c:5,6-c]difuran: a reactive linker and cyclophane precursor.

Naphtho[1,2-c:5,6-c]difuran has been isolated in a 9-step synthesis from 2,6-dimethylnaphthalene. It is a highly reactive diene similar in nature to the related isobenzofuran. In Diels-Alder reactions, its intermediate monoadducts are actually less reactive that the parent difuran making possible sequential Diels-Alder reactions with different dienophiles. Reaction with a tethered bis(dienophile) leads to the production of a naphthalenic cyclophane.

Knoevenagel Adducts from Reactions Between Glutaconate Moieties and Aldehydes and Their Adducts with Primary Amines and Enamines.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Liquid-phase synthesis of 2,3-dihydro-4-pyridones: one-pot three-component aza Diels–Alder reaction of Danishefsky's diene with aldehydes and PEG-supported amine

An efficient liquid-phase synthesis technique for the construction of 2,3-dihydro-4-pyridones on soluble polymer support has been developed, which utilized one-pot reaction of Danishefsky's diene with aldehydes and polymer-supported amine.

Diels—Alder Reaction. Effect of Internal and External Factors on the Reactivity of Diene—Dienophile Systems

AbstractFor Abstract see ChemInform Abstract in Full Text.

Chiral Transition Metal Lewis Acids Bearing Bis(oxazolinyl)phenyl (Phebox) as a Pincer Ligand: Synthesis and Application for the Asymmetric Reactions

AbstractFor Abstract see ChemInform Abstract in Full Text.

Reactions of ( S)-(+)-4-ethenyl[2.2]paracyclophane with heterocyclic quinones

The reactions of ( S)-(+)-4-ethenyl[2.2]paracyclophane 1 and 1-vinylnaphthalene 11 with quinoline-5,8-dione 2 and isoquinoline-5,8-dione 3 have been studied under high pressure and Lewis acid-catalyzed conditions. In contrast to the reactivity of diene 11, diene 1 was found to add to quinones 2 and 3 in an abnormal fashion. A structural analysis of the reaction products by 1H and 13C NMR spectroscopy is presented.

Calix[ n]arene/Ti(IV) complexes as active catalysts in aldol reaction of Chan's diene

The aldol condensation of Chan's diene with benzaldehyde is catalyzed by only 8% mol of the calix[ n]arene/Ti(O- i-Pr) 4 complexes. Studies have revealed that the size of calixarene molecule and the number of hydroxyl groups affected the efficiency of the reaction. The reaction conditions (solvent and temperature) have been examined.

An ionic liquid-supported ruthenium carbene complex: a robust and recyclable catalyst for ring-closing olefin metathesis in ionic liquids.

The synthesis of an ionic liquid-supported olefin metathesis catalyst derived from Grubb's ruthenium carbene complex is described. This new supported catalyst has been used in BMI.PF6 solvent, and this allowed success in solving the challenging problem of catalyst recycling. The IL catalyst in BMI.PF6 can be recovered and reused up to 10 consecutive cycles in RCM reactions of several dienes with excellent conversions. Moreover, the IL catalyst shows a remarkable stability in BMI.PF6 and can be stored several months without loss of activity. These results clearly demonstrate the importance of anchoring an imidazolium ionic liquid pattern to the catalyst to avoid its leaching from the BMI.PF6 phase.

Highly Stereoselective Hydroxy‐Directed Diels—Alder Reaction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

AgOTf‐Catalyzed Aza‐Diels—Alder Reactions of Danishefsky′s Diene with Imines in Water.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of Dendritic Schiff Base Ligands for Titanium Catalyzed Enantioselective HDA Reaction of Danishelfsky's Diene with Aldehydes

AbstractA new type of dendritic NOBIN derived Schiff base ligands has been synthesized and applied to titanium catalyzed hetero‐Diels‐Alder reaction of Danishelfsky's diene and aldehydes, affording the corresponding 2‐substituted 2,3‐dihydro‐4H‐pyran‐4‐one in good yields and moderate enantioselectivities (up to 59.2% ee). It was found that the size of dendron attached to the tri‐dentated ligands has slight impact on the enantioselectivity of the reaction and the second generation of dendritic ligand exhibited the best enantioselectivity.

Pi-Facial stereoselectivity in Diels-Alder cycloadditions to 1-oxaspiro[4.5]deca-6,9-dien-8-one. The strong directive effect of ether oxygen in a cross-conjugated ketone setting.

[reaction: see text] The title compound 1, prepared from 1,4-cyclohexanedione monoethylene ketal, was treated with several reactive dienes, including diphenylisobenzofuran and 9,10-dihydro-11,12-dimethylene-9,10-ethanoanthracene. These [4 + 2] cycloadditions proceed with a strong kinetic bias for bonding to the dienophile from the direction syn to the tetrahydrofuranyl oxygen and consequently hold value in stereoselective synthesis.