Free Radical Cyclization Reactions Research Articles

Investigation on the Edge Doping Process of Nitrogen-Doped Carbon Materials by In Situ Pyrolysis Mass Spectrometry and Laser-Induced Acoustic Desorption Mass Spectrometry

Nitrogen-doped carbon materials demonstrate high performance as electrodes in fuel cells and higher oxygen reduction reactivity than traditional Pt-based electrodes. However, the formation process of nitrogen-doped carbon materials has long been a mystery. In this study, the formation mechanism of nitrogen-doped carbon materials from polyaniline (PANI) pyrolysis was studied by the combination of in situ pyrolysis vacuum ultraviolet photoionization time-of-flight mass spectrometry (Py-VUVPI-TOF MS) and substrate-enhanced, laser-induced acoustic desorption source time-of-flight mass spectrometry (SE-LIAD-TOF MS). The initial pyrolysis species, including free radicals and intermediates, were investigated via in situ Py-VUVPI-TOF MS during the temperature-programmed desorption process (within tens of microseconds). The pyrolysis residues were collected and further investigated via SE-LIAD-TOF MS, revealing the product information of the initial pyrolysis products. The results show that the edge doping of carbon materials depends on free radical reactions rather than the direct substitution of carbon atoms by nitrogen atoms. Meanwhile, pyrrole nitrogen and pyridine nitrogen are formed by the free radical cyclization reaction and the amino aromatization reaction at the initial stage of pyrolysis, while the formation of graphitic nitrogen depends on the further polymerization reaction of pyrrole nitrogen and pyridine nitrogen.

Directed Copper-Catalyzed Tandem Radical Cyclization Reaction of Alkyl Bromides and Unactivated Olefins.

The free radical cyclization reaction is a promising strategy for ring framework formation. Herein, we report a copper-catalyzed tandem radical cyclization strategy for preparing substituted lactam derivatives. This reaction proceeds through a radical coupling approach, which not only allows a wide range of alkenes but also is quite compatible with the primary, secondary, and tertiary radicals. In addition, density functional theory calculations were performed to gain insights into the reaction mechanism.

A Free Radical Cyclization Catalyzed by Ruthenium Hydride Species.

A photolytically generated ruthenium hydride species catalyzing a free radical cyclization reaction was developed. As the new methodology ensures reproducibility of the free radical reaction of trialkyltin hydrides and a fast hydrogen transfer to the radical intermediates, the methodology provides fast quenching of radical intermediates and thus suppresses rearrangement of radical intermediates before the hydride quench. By offering new reactivity and selectivity to the trialkyltin hydride mediated free radical cyclization reactions, the methodology will find wide range of applications in organic synthesis.

Total Synthesis of (±)-Crinane from 6,6-Dibromobicyclo[3.1.0]hexane Using a 5- exo- trig Radical Cyclization Reaction to Assemble the C3a-Arylated Perhydroindole Substructure.

Crinane embodies the tetracyclic framework associated with some of the most common Amaryllidaceae alkaloids. It has now been prepared in 10 steps from 6,6-dibromobicyclo[3.1.0]hexane (2). The initial step involves the thermally induced electrocyclic ring opening of cyclopropane 3 and capture of the resulting π-allyl cation with benzylamine to give an allylic amine that is readily elaborated to the 3°-amine 10. This last compound was engaged in a 5- exo- trig free radical cyclization reaction to give the C3a-arylated perhydroindole 11. Compound 11 was then converted, over two steps, into (±)-crinane, the hydrochloride salt of which has been subjected to single-crystal X-ray analysis.

Simultaneous DSC/TG analysis on the thermal behavior of PAN polymers prepared by aqueous free-radical polymerization

A series of polyacrylonitrile (PAN) polymers with different content of itaconic acid (IA) as comonomer were prepared by an efficient aqueous free-radical polymerization technique. The thermal behavior of the PAN polymers was investigated by simultaneous DSC/TG analysis. Effects of IA content, heating rate and atmosphere on the heat release and weight loss behaviors of the PAN polymers were studied for insight of the nature of the thermo-chemical reactions. A specific triple exothermic peak was observed in the DSC curves of P(AN-IA) copolymers in air atmosphere. Three individual exothermic peaks were obtained by peak fitting and assigned to the respective thermo-chemical reactions, namely, ionic cyclization reaction, free-radical cyclization reaction and oxidation reaction. The ionic cyclization reaction was significantly influenced by the IA content. The free-radical cyclization reaction was sensitive to heating rate and atmosphere. The cyclization reaction preceded the oxidation reaction and acted as a prerequisite for the oxidation reaction. The improvement of the thermal stability of PAN was mainly attributed to the oxidation reaction through dehydrogenation and formation of oxygen-bearing groups. Mechanisms of the thermo-chemical reactions were also proposed and discussed.

Construction of functionalized ABEF ring system of C20-diterpenoid alkaloid racemulosine

A continued effort to synthesis of functionalized ABEF tetracyclic ring system of structurally complex C20-diterpenoid alkaloid racemulosine from previously reported tetracyclic aziridine intermediate 3 was described. The synthesis features a regio- and stereoselective ring opening of aziridine and a challenging free radical cyclization reaction to construct functionalized ring B, which could provide a good basis for total synthesis of racemulosine.

Theoretical study on the mechanism and kinetics of atmospheric reactions C n H2n+2 + NH2 (n = 1–3)

Mechanism and kinetics of the gas phase reactions of C n H2n+2 (n = 1–3) with NH2 were studied using the B3LYP and MP2 methods. The considered reactions were both hydrogen abstraction and substitution reactions. The calculated values of activation energies for hydrogen abstraction reactions were less than 80 kJ/mol and those for substitution reactions were about 230 kJ/mol. Formation of six heterocyclic molecules (I–VI) through free-radical cyclization reaction was investigated. The calculated values of activation energies for the radical cyclization reactions were about 200 kJ/mol. The rate constants of the reactions were calculated using transition state theory at 298 K.

Initiated chemical vapor deposition and light-responsive cross-linking of poly(vinyl cinnamate) thin films.

The first vapor-phase deposition of poly(vinyl cinnamate) (PVCin) is reported. Initiated chemical vapor deposition (iCVD) is used to synthesize PVCin thin films with an average thickness of 100 nm. Free radical polymerization and cyclization reactions compete during the deposition process, with approximately 45% of the repeat units undergoing cyclization. Exposure to UV light (λ = 254 nm) induces dimerization (cross-linking) of the PVCin, which is quantified using spectroscopic techniques. Approximately 90% of the free cinnamate moieties are dimerized at a UV dose of 300 mJ cm(-2) . PVCin is also incorporated into a copolymer with N-isopropylacrylamide, which exhibits a characteristic change in hydrophilicity with temperature. The copolymer is selectively cross-linked through a mask, and reversible swelling of patterns with 30 μm resolution is demonstrated by submerging the film in water.

Total synthesis of zyzzyanones A–D

Zyzzyanones A–D is a group of biologically active marine alkaloids isolated from Australian marine sponge Zyzzya fuliginosa. They contain a unique bispyrroloquinone ring system as the core structure. The first total synthesis of all four zyzzyanones is described here. The synthesis of these alkaloids started from a previously known 6-benzylamino indole-4,7-quinone derivative and involves 6–7 steps. The key step in the synthesis involves the construction of a pyrrole ring in one step using a Mn(OAc)3 mediated oxidative free radical cyclization reaction of a 6-benzylamino indole-4,7-quinone derivative with 4-benzyloxyphenyl acetaldehyde diethyl acetal in CH3CN.

Free radical cyclization reactions of allylsulfonyl substituted N-aryl amide derivatives

p-Toluenesulfonyl radical can be generated by the manganese(III) acetate oxidation of sodium p-toluenesulfinate. The corresponding alkyl radicals could be produced effectively by the p-toluenesulfonyl radical induced radical reaction of allylsulfonyl substituted N-aryl amides. These alkyl radicals undergo 5-exo-trig, 6-endo-trig, or 6-exo-trig cyclization onto the aromatic ring effectively. The product distribution is highly dependent on the substituent of aromatic ring and the stability of radical intermediate. This p-toluenesulfonyl radical induced reaction provides a synthetically useful method for the synthesis of dihydroquinolinones, azaspirocyclic cyclohexadienes, and spirodihydroquinolinones.

Synthesis of Pyrroloquinones via a CAN Mediated Oxidative Free Radical Reaction of 1,3-Dicarbonyl Compounds with Aminoquinones.

Pyrroloquinone ring systems are important structural units present in many biologically active molecules including a number of marine alkaloids. For example, they are found in a series of marine metabolites, such as tsitsikammamines, zyzzyanones, wakayin, and terreusinone. Several of these alkaloids have exhibited antimicrobial, antimalarial, antifungal, antitumor, and photoprotecting activities. Synthesis of pyrroloquinone unit is the key step in the synthesis of many of these important organic molecules. Here, we present a ceric (IV) ammonium nitrate (CAN) mediated oxidative free radical cyclization reaction of 1,3-dicarbonyl compounds with aminoquinones as a facile methodology for making various substituted pyrroloquinones. 1,3-dicarbonyl compounds used in this study are ethyl acetoacetate, acetylacetone, benzoyl acetone, and N,N-dimethyl acetoacetamide. The aminoquinones used in this study are 2-(benzylamino)naphthalene-1,4-dione and 6-(benzylamino)-1-tosyl-1H-indole-4,7-dione. The yields of the synthesized pyrroloquinones ranged from 23–91%.

ChemInform Abstract: Intramolecular Free‐Radical Cyclization Reactions on Pentose Sugars for the Synthesis of Carba‐LNA and Carba‐ENA and the Application of Their Modified Oligonucleotides as Potential RNA Targeted Therapeutics

AbstractReview: 107 refs.

Steric Effects in the Tuning of the Diastereoselectivity of the Intramolecular Free-Radical Cyclization to an Olefin As Exemplified through the Synthesis of a Carba-Pentofuranose Scaffold

Two free-radical cyclization reactions with the radical at the chiral C4 of the pentose sugar and the intramolecularly C1-tethered olefin (on radical precursors 8 and 17) gave a new diastereospecific C4-C8 bond in dimethylbicyclo[2.2.1]heptane 9, whereas the new C4-C7 bond in 7-methyl-2-oxabicyclo[2.2.1]heptanes 18a/18b gave trans and cis diastereomers, in which the chirality of the C4 center is fully retained as that of the starting material. It has been shown how the chemical nature of the fused carba-pentofuranose scaffolds, dimethylbicyclo[2.2.1]heptane 9 vis-a-vis 7-methyl-2-oxabicyclo[2.2.1]heptanes 18a/18b (C7-Me in the former versus 2-O- in the latter), dictates the stereochemical outcome both at the Grignard reaction step as well as in the free-radical ring-closure reaction. The formation of pure 1,8-trans-bicyclo[2.2.1]heptane 9 from 8 suggests that the boat-like transition state is favored due to the absence of steric clash of the bulky 1(S)-O-p-methoxybenzyl (PMB) and 7(R)-Me substituents (both in the α-face) with that of the 8(R)-CH(2)(•) radical in the β-face. The conversion of 17 → 18a-7(S) and 18b-7(R) in 6:4 ratio shows that the participation of both the chair- and the boat-like transition states is likely.

Intramolecular Free-Radical Cyclization Reactions on Pentose Sugars for the Synthesis of Carba-LNA and Carba-ENA and the Application of Their Modified Oligonucleotides as Potential RNA Targeted Therapeutics

Intramolecular Free-Radical Cyclization Reactions on Pentose Sugars for the Synthesis of Carba-LNA and Carba-ENA and the Application of Their Modified Oligonucleotides as Potential RNA Targeted Therapeutics

ChemInform Abstract: Organosilane-Mediated Free Radical Cyclization Reactions Employing Carbonyl Traps.

ChemInform Abstract: Organosilane-Mediated Free Radical Cyclization Reactions Employing Carbonyl Traps.

ChemInform Abstract: Investigation of Mn(III)-Based Oxidative Free Radical Cyclization Reactions Toward the Synthesis of Triptolide: The Effects of Lanthanoid Triflates and Substituents on Stereoselectivity.

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First-Principles Prediction of Rate Coefficients for Free-Radical Cyclization Reactions at Selenium

High-level ab initio calculations of the barriers, enthalpies, and rate coefficients for the intramolecular cyclization reactions of *CH(2)CH(2)CH(2)CH(2)SeR (R = Me, n-Bu, s-Bu, t-Bu, Bn, Bz, Ph(2)CH) and *CH(2)CH(2)CH(2)CH(2)CHCH(2) have been performed at the G3(MP2)-RAD level. The calculated rate coefficients show excellent agreement with experiment (to within a factor of 5 or better), although this might be due, in part, to a systematic cancelation of order-of-magnitude errors in the corresponding Arrhenius parameters. The intramolecular cyclizations at selenium were found to be energetically favorable processes that occur with synthetically accessible rate coefficients on the order of 10(4)-10(6) s(-1) at 294 K. These values are largely governed by the stabilization energy of the leaving radical, though with contributions from steric and polar effects.

DSC study of stabilization reactions in poly(acrylonitrile-co-itaconic acid) with peak-resolving method

The effect of itaconic acid (IA) content and heating rate on the stabilization reactions in poly(acrylonitrile-co-itaconic acid) (P(AN-co-IA)) was investigated by differential scanning calorimetry (DSC) with peak-resolving method. Increasing IA content was effective in decreasing the initial temperature and the heat evolved, and found to enhance oxidative reactions to some extent. While, promoting heating rate resulted in a shift of the exotherm to a higher temperature and a more rapid liberation of heat. The percentage of area of the first exothermic peak increased with increasing heating rate, which would be attributed to the enhancement of the free radical cyclization reactions.

Free‐Radical Approaches to Stemoamide and Analogues.

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Free-Radical Approaches to Stemoamide and Analogues

Two approaches allowing access to the tricyclic stemona backbone are presented. Both approaches rely on a free-radical cyclization reaction as the key step. In the formal synthesis of (+/-)-stemoamide, the construction of the A ring of the natural product was achieved via a 5-exo-trig radical cyclization with atom transfer. The two diastereoisomers issuing from this cyclization showed different reactivity while forming the seven-membered ring of the final product. In the second part of this study, a 7-exo-trig free radical cyclization was realized allowing access to the (+/-)-9,10-bis-epi-stemoamide. This reaction was highly stereoselective and allowed the control of three of the four contiguous stereocenters present in the molecule.