Presence Of Dienes Research Articles

Use of Formic Acid as a CO Surrogate for the Reduction of Nitroarenes in the Presence of Dienes: A Two‐Step Synthesis of N‐Arylpyrroles via 1,2‐Oxazines

AbstractFormic acid, activated by acetic anhydride and a base, was employed as a CO surrogate to deoxygenate nitroarenes to nitrosoarenes, a reaction catalyzed by a palladium/phenanthroline complex in the homogeneous phase. Nitrosoarenes were trapped by conjugated dienes to give 3,6‐dihydro‐2H‐[1,2]‐oxazines. The latter were then transformed into N‐arylpyrroles employing CuCl as the catalyst. The reaction was designed to give the best results for pyrroles lacking any substituent in the 2 and 5 positions, which are difficult to produce employing most pyrrole syntheses.

Derivatization and biological activity studies of 3-chloro-3-chlorosulfenyl spiro tetrahydropyran/tetrahydrothiopyran-4,2'-chroman-4'-one

The adducts 4a,b-7a , b have been obtained either by reducing α-chloro-β-oxosulfenyl chlorides 2a,b with iodide ion in the presence of dienes namely, 2-methyl-1,3-butadiene (isoperene), 2,3-dimethyl-1,3-butadiene, 1,2,3,4-tetrachlorocyclopentadiene, or 1,3-cyclohexadiene, respectively; or by thermolysis of oxadithiin derivatives 3a,b in the presence of the same aforementioned dienes presumably via the formation of the same intermediate A in both cases of compounds 2a,b and 3a,b . It is observed that α-chloro-β-oxosulfenyl chlorides 2a,b undergo straight forward substitution with potassium cyanide to give 8a,b . Direct oxidation of 2a,b with H 2 O 2 /AcOH affords 3,3-dichloropyran-4-ones 9a,b , while conversion of 2a,b to the sulfonamides 10a,b followed by oxidation provides 3-chloropyranones 11a,b . Antioxidant and antimicrobial evaluation of compounds 4a,b-6a,b shows moderate activiy. MIC of the derivative 6b reveals a remarkable inhibition of the pathogenic gram positive bacteria ( Staphylococcus aureus ) as well as gram negative E coli .

Photoactivation of Organotellurium Compounds in Precision Polymer Synthesis: Controlled Radical Polymerization and Radical Coupling Reactions

Abstract Organotellurium chain transfer agents (CTAs) used for organotellurium-mediated radical polymerization (TERP) are highly photosensitive and generate radicals by carbon-tellurium bond homolysis upon absorbing UV-vis light at approximately 350–500 nm. The controlled radical polymerization of various vinyl monomers takes place in the presence of organotellurium CTAs under photoirradiation. The use of low-intensity light is important to attain structural control because of the need to maintain a low radical concentration. Photo-TERP not only preserves the synthetic advantages of TERP under thermal conditions, as exemplified by its high versatility in polymerizable monomer families, but also attains new benefits, including decreasing the amount of dead polymers, increasing the control of the macromolecular structure, lowering the polymerization temperature, and providing temporal control. In contrast, irradiation of a polymer prepared by TERP in the presence of dienes and styrenes with high-intensity light selectively gives the dimer via a polymer-end radical coupling reaction. Various symmetrical telechelic and mid-chain-functionalized polymers and ABA-triblock copolymers can be synthesized. Due to the mild conditions for both photo-TERP and the coupling reaction, unique macromolecular structures, and high structural control, these methods provide a new method in macromolecular engineering for fabricating functional polymer materials with improved and/or new functions.

Syntheses and Catalytic Hydrogenation Performance of Cationic Bis(phosphine) Cobalt(I) Diene and Arene Compounds

AbstractChloride abstraction from [(R,R)‐(iPrDuPhos)Co(μ‐Cl)]2 with NaBArF4 (BArF4=B[(3,5‐(CF3)2)C6H3]4) in the presence of dienes, such as 1,5‐cyclooctadiene (COD) or norbornadiene (NBD), yielded long sought‐after cationic bis(phosphine) cobalt complexes, [(R,R)‐(iPrDuPhos)Co(η2,η2‐diene)][BArF4]. The COD complex proved substitutionally labile undergoing diene substitution with tetrahydrofuran, NBD, or arenes. The resulting 18‐electron, cationic cobalt(I) arene complexes, as well as the [(R,R)‐(iPrDuPhos)Co(diene)][BArF4] derivatives, proved to be highly active and enantioselective precatalysts for asymmetric alkene hydrogenation. A cobalt–substrate complex, [(R,R)‐(iPrDuPhos)Co(MAA)][BArF4] (MAA=methyl 2‐acetamidoacrylate) was crystallographically characterized as the opposite diastereomer to that expected for productive hydrogenation demonstrating a Curtin–Hammett kinetic regime similar to rhodium catalysis.

Syntheses and Catalytic Hydrogenation Performance of Cationic Bis(phosphine) Cobalt(I) Diene and Arene Compounds.

Chloride abstraction from [(R,R)-(iPr DuPhos)Co(μ-Cl)]2 with NaBArF 4 (BArF 4 =B[(3,5-(CF3 )2 )C6 H3 ]4 ) in the presence of dienes, such as 1,5-cyclooctadiene (COD) or norbornadiene (NBD), yielded long sought-after cationic bis(phosphine) cobalt complexes, [(R,R)-(iPr DuPhos)Co(η2 ,η2 -diene)][BArF 4 ]. The COD complex proved substitutionally labile undergoing diene substitution with tetrahydrofuran, NBD, or arenes. The resulting 18-electron, cationic cobalt(I) arene complexes, as well as the [(R,R)-(iPr DuPhos)Co(diene)][BArF 4 ] derivatives, proved to be highly active and enantioselective precatalysts for asymmetric alkene hydrogenation. A cobalt-substrate complex, [(R,R)-(iPr DuPhos)Co(MAA)][BArF 4 ] (MAA=methyl 2-acetamidoacrylate) was crystallographically characterized as the opposite diastereomer to that expected for productive hydrogenation demonstrating a Curtin-Hammett kinetic regime similar to rhodium catalysis.

Modular Synthesis of Mid-Chain-Functionalized Polymers by Photoinduced Diene- and Styrene-Assisted Radical Coupling Reaction of Polymer-End Radicals

Photoirradiation of structurally well-defined “living” polymers prepared by organotellurium-mediated living radical polymerization in the presence of dienes or styrenes induced selective polymer-end coupling reaction with the concomitant insertion of the dienes or styrenes with >90% coupling efficiency. The number of inserted dienes or styrenes could be highly controlled to two molecules when acrylic polymers were used. Therefore, various mid-chain-functionalized polymers with well-controlled molecular and macromolecular structure in terms of their molecular weight, molecular weight distribution, functionality, and position were successfully synthesized by employing functionalized dienes or styrenes. The method was applied to the facile synthesis of mid-chain-functionalized telechelic polymers and a 4-miktoarm star polymer with a well-controlled structure.

The Oxidative Acylnitroso Hetero-Diels-Alder Reaction Catalyzed by Dirhodium Caprolactamate

An effective protocol is described for the generation and in situ Diels–Alder trapping of acylnitroso derivatives. In this procedure, the oxidation of hydroxamic acid is efficiently catalyzed by dirhodium(II) caprolactamate with <i>tert</i>-butyl hydroperoxide (TBHP) in the presence of dienes at room temperature. Using this approach we obtained a variety of hetero-Diels–Alder cycloadducts in yields of up to 96% at 0.1 mol% catalyst loading.

ChemInform Abstract: Addition of Aromatic Amines to Conjugated Dienes in Presence of Thallium(III) Acetate.

ChemInform Abstract: Addition of Aromatic Amines to Conjugated Dienes in Presence of Thallium(III) Acetate.

ChemInform Abstract: The Mild Oxidation of Nitrile Oxides Affords a Convenient Entry to Nitrosocarbonyl Intermediates, Versatile Tools in Organic Syntheses.

Abstract Nitrile oxides are oxidized by tertiary amine N-oxides in different solvents at room temperature to afford in the presence of dienes nitrosocarbonyl adducts in fair yields. The mild conditions used in oxidizing a variety of nitrile oxides promise a wide application of this method in synthetic processes.

Triplet Energy Transfer Insight in Coordination of Unsaturated Hydrocarbons by d0Bent Metallocenes (Zr, Hf)

For a class of pi-complexes as energy donors, with the use of highly emissive d(0) metallocenes Cp(2)MCl(2) where M = Zr and Hf, it is shown that radiationless triplet energy transfer to unsaturated hydrocarbons in a rigid nonpolar methylcyclohexane (MCH) matrix (where molecular diffusion is absent) obeys the Perrin equation, occurs at radii R(0), being close to the diameter of interacting molecules, and is well described by an electron-exchange resonant (Dexter) mechanism of interaction. Principle correlation between values of the critical radius and a number of C atoms in a linear alpha-olefin is for the first time reported, viz. R(0) (Angstrom) = -2.47 + 1.35n (obtained for systems [Cp(2)HfCl(2) + CnH(2)n + MCH] at 77 K). Pronounced blue shifts (up to 1000 cm(-1)) of low-temperature emission spectra of Cp(2)ZrCl(2) in MCH in the presence of dienes, possessing nonconjugated C=C bonds, are observed, thus suggesting inner-sphere diene coordination. In view of the experimental data, inner- and outer-sphere coordinative interaction between the components of catalytic systems for polymerization (d(0) metallocene precatalysts and alkenes and dienes) is rationalized.

Alternative syntheses of the D2d symmetric 1,3,5,7-tetraiodotricyclo[3.3.0.03,7]octane

Three alternative syntheses of 1,3,5,7-tetraiodotricyclo[3.3.0.03,7]octane are described. Reaction of this tetraiodide with sodium amalgam in the presence of dienes or with molten sodium in boiling 1,4-dioxane in the absence of trapping agents led to very complex mixtures of products, presumably due to competitive 1,2- and 1,3-deiodination reactions.

Diastereo- and regioselectivity in Diels–Alder reaction of [1,4,2]diazaphospholo[4,5- a]pyridines

[1,4,2]Diazaphospholo[4,5- a]pyridines undergo diastereoselective Diels–Alder reaction at the >C P– functionality with 2,3-dimethylbutadiene and isoprene in the presence of sulfur or selenium. The reaction with isoprene occurs regioselectively. On carrying out the reaction with diene in presence of methyl iodide, the initially formed [2+4] cycloadduct is methylated regioselectively at the σ 2, λ 3-nitrogen. The results of the DFT calculations of the Diels–Alder reaction with isoprene are in accord with the observed regioselectivity. The relative stabilities of the two transition structures have been explained on the basis of NBO analysis.

Dehalogenation of o‐Dihalogen Substituted Arenes and α,α′‐Dihalogen Substituted o‐Xylenes with Lanthanum Metal.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Dehalogenation of o-dihalogen substituted arenes and α,α′-dihalogen substituted o-xylenes with lanthanum metal

It was found that lanthanum metal caused the dehalogenation of o-dihalogen substituted arenes and α,α′-dihalogen substituted o-xylenes to generate the corresponding benzynes and o-quinodimethanes. When o-dihalogen substituted arenes were allowed to react with lanthanum metal in the presence of dienes, the Diels–Alder products between benzyne and dienes were formed in moderate to good yields. Similarly, the Diels–Alder adducts of o-quinodimethane with dienophiles were obtained, in the reaction of α,α′-dibromo- o-xylenes with lanthanum metal in the presence of dienophiles.

Reaction of 1,2‐Dihalogen‐Substituted Arenes with Lanthanum Metal: A New Generation Method of Benzyne.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Diastereoselective formation of cage-type adducts via a novel photoreaction of nicotinic acid esters with furan

Irradiation of a benzene solution containing 2-alkoxynicotinic acid esters (0.02 M) and furan (0.2 M) resulted in the formation of cage-type adducts in 73–84% yield. The structure of the adducts was established by X-ray crystallographic analysis. The mechanism involving 4π+4π photocycloaddition between the pyridine ring and furan was postulated. Two diastereomeric 4π+4π adducts were detected as intermediates in the 1H NMR spectroscopy, when the solution was irradiated in the presence of diene as a triplet quencher.

Reaction of 1,2-dihalogen substituted arenes with lanthanum metal: a new generation method of benzyne

A new generation method of benzyne has been developed. When 1,2-dihalogen substituted arenes were allowed to react with lanthanum metal in the presence of dienes, Diels–Alder products between benzyne and dienes were formed in moderate to good yields.

Effect of Hydrocarbonaceous Deposits on Competitive Hydrogenation of 1,3-Butadiene and Propene over Pd Catalyst

Gas phase hydrogenation of 1,3-butadiene, propene, and mixtures of 1,3-butadiene and propene has been investigated over 0.05 wt% Pd/Al2O3catalyst. The catalyst was deliberately poisoned by methane (513 K) or diene (473 K) and the effect of the hydrocarbonaceous materials was tested on the product selectivity and the rate of hydrogenation of diene–propene mixtures. It has been concluded that a large quantity of hydrocarbonaceous deposit decreases the surface fugacity of diene due to transport hinderance and in consequence enhances the over-hydrogenation of diene and permits the hydrogenation of propene in the presence of diene.

Electrochemical Oxyphenylselenation of Dienes

. The electrochemical oxidation of diphenyl diselenide in the presence of dienes affords the corresponding cyclic β-phenylselenoethers via an oxyphenylselenation process. The yields of ethers depend on the nature of the diene and on the reaction temperature..

Synthesis and structure of ruthenium(II)-diene complexes

The reaction of Ru(acac) 3 in ethanol in the presence of dienes (diene = 2,5-dimethyl-2,4-hexadiene, isoprene, 1,2,4,5-tetramethyl-1,4-cyclohexadiene) with zinc as reducing agent affords Ru(acac) 2(diene) complexes. For the acyclic diene ligands, the Ru(acac) 2 unit exhibits a preference for the trans-diene coordination. The structures for the 2,5-dimethyl-1,3-hexadiene and 1,2,4,5-tetramethyl-1,4-cyclohexadiene derivatives have been determined crystallographically. The Ru(acac) 2(hexadiene) complex crystallizes in the monoclinic space group P2 1/ n with a = 10.658(2) A ̊ , b = 12.075(3) A ̊ , c = 15.332(3) A ̊ and β = 108.07(5)° for Z = 4 . The cyclohexadiene complex crystallizes in a triclinic space group P I , with a = 8.495(4) A ̊ , b = 8.456(4) A ̊ , c = 14.364(6) A ̊ , and α = 78.88(2)°, β = 82.60(2)°, γ = 78.04(2)° for Z = 2 . The solid-state structure for the dimethylhexadiene complex revealed an η 4- trans-diene coordination, while for the cyclic diene it revealed isolated olefin interactions.