Radical Addition Cyclization Research Articles

Understanding of the effect of oxygen on soot formation during non-catalytic partial oxidation process

Non-catalytic partial oxidation (NC-POX) process is a promising technology for hydrogen and syngas production, but the generation of soot hinders its development. In this study, the yields of soot and its precursors under different working conditions are quantified by experiments. When the O2/CH4 ratio is more than 0.6, the soot yield can be controlled below 1.07% from 2.53%. The soot precursor evolution mechanism in NC-POX is analyzed through the quantification of polycyclic aromatic hydrocarbon (PAH) compounds. It is found that hydrogen abstraction vinyl radical addition (HAVA*) and methyl addition cyclization (MAC) are the main growth pathways of PAHs. The concentrations of H2O, CO2, and oxygenated hydrocarbons increase with O2/CH4, which further inhibit the soot generation reactions and reduce the degree of graphitization of soot particles through surface reactions. A soot formation mechanism is proposed. This study provides a quantified reference for soot modeling and the elimination of soot in industry.

Chiral Acyl Radicals Generated by Visible Light Enable Stereoselective Access to 3,3-Disubstituted Oxindoles: Application toward the Synthesis of (–)- and (+)-Physovenine

AbstractExploration of the repurposing of N-acyl chiral auxiliaries for use as novel chiral C1 radical synthons is reported. The acyl radicals are generated under visible-light-mediated single-electron transfer of N-hydroxyphthalimido ester, and their use toward the stereoselective synthesis of 3,3-disubstituted oxindoles via a radical addition–cyclisation sequence is demonstrated. The downstream synthetic utility of this method is showcased in the formal synthesis of the natural product (–)-physovenine. TEMPO trapping experiments support the proposed reaction mechanism.

Visible‐light‐promoted Cascade Reaction of Acryloylbenzamides with Carboxylic Acids: Metal‐free Synthesis of Isoquinolinediones

AbstractA metal‐free and mild cascade reaction of acryloylbenzamides with carboxylic acids and α‐imino oxy acid is developed. It undergoes decarboxylation, radical addition, and intramolecular cyclization in the presence of visible light, providing 4‐substituted‐isoquinoline‐1,3(2H,4H)‐diones in moderate to good yields.

Strategy Analysis of Ynones’ Radical Reactions

: This review highlights the multifaceted synthetic applications of ynones in radical reactions. Substantial progress has been made over the last decade (2010-2020) in the utilization of ynones. Herein, the chemistry of ynones is divided into three sections based on the classes of critical mechanistic insights: (1) radical addition and intramolecular cyclization; (2) radical addition and intermolecular annulation; (3) radical addition and coupling. We hope that this review will promote future research in this area.

Formation behavior of PAHs during pyrolysis of waste tires

Polycyclic aromatic hydrocarbons (PAHs) formation from the pyrolysis of waste tires is inevitable because of the complexity of tire formulations and the addition of certain chemicals. In this study, the formation behavior and distribution of PAHs in three-phases were investigated from waste tires under pyrolysis conditions. The influencing factors including the temperature, heating rate, holding time, particle size, catalyzer, and atmosphere, were systematically evaluated. The results showed that PAHs were mainly concentrated in pyrolysis oil (94.59–99.03%), followed by the gas phase (0.96–5.34%), and their content was very low in the solid phase (0.01–0.99%). A higher temperature and slower heating rate lead to partial PAHs decomposition, thus reducing their emissions. The overall formation of PAHs can be inhibited when pyrolyzing coarse-grained tire powder. Furthermore, the PAHs formation mechanisms in waste tires were determined through reaction molecular dynamics, electron paramagnetic resonance, and intermediate products. Tires were mainly decomposed into benzene series, *C2H3, and *CH3; therefore, it was determined that PAHs were formed by the joint action of the hydrogen abstraction, and vinyl radical addition and methyl addition cyclization mechanisms. Among them, low and middle-ring PAHs were formed more easily, particularly naphthalene. The generation of PAHs can be inhibited by reducing the concentration of hydrocarbons and monocyclic benzene series. Regarding the distribution law and generation pathways of PAHs, our results provide guidance for reducing PAHs formation and emissions.

Visible light-induced radical cascade reaction of acryloylbenzamides with N-hydroxyphthalimide esters

An efficient and mild cascade reaction of acryloylbenzamides with N-hydroxyphthalimide (NHPI) esters is disclosed. It goes through radical addition and subsequent cyclization to give 4-alkylated isoquinolinediones in the presence of visible light and photocatalyst Ir[dF(CF3)ppy2](dtbbpy)PF6.

A radical addition and cyclization relay promoted by Mn(OAc)3⋅2H2O: Synthesis of 1,2-oxaphospholoindoles and mechanistic study

Novel and efficient Mn(OAc)3⋅2H2O promoted radical addition-[4 + 1] cyclization relay of 3-indolymethanols and phosphites was disclosed, which afforded 1,2-oxaphospholoindole derivatives in moderate to good yields. Based on the experimental and computational studies, a mechanism involving radical addition and intramolecular cyclization cascade was proposed.

Oxidant- and Catalyst-Free Synthesis of Sulfonated Benzothiophenes via Electrooxidative Tandem Cyclization.

A green and practical electrochemical method for the synthesis of C-3-sulfonated benzothiophenes from 2-alkynylthioanisoles and sodium sulfinates was developed under oxidant- and catalyst-free conditions. Moderate to good yields of sulfonated benzothiophenes bearing important and useful functional groups have been achieved at a constant current. Preliminary mechanistic studies indicated a tandem radical addition-cyclization pathway. Moreover, the protocol is easy to scale up and exhibits good reaction efficiency.

One‐Step Synthesis of Trifluoroethylated Chromones via Radical Cascade Cyclization–Coupling of 2‐(Allyloxy)arylaldehydes

A transition‐metal‐free synthetic protocol involved with trifluoromethyl radical addition–cyclization of 2‐(allyloxy)arylaldehydes for a series of CF3‐containing 3‐substituted chromenones formation has been developed. The radical cascade cyclization–coupling reaction can be run in a one‐step manner with Langlois′ reagent (CF3SO2Na) and K2S2O8. Broad scopes of substrates with various functional groups are evaluated in moderate to good efficacy under operational simplicity and mild reaction conditions. A plausible mechanism for the construction of trifluoroethylated chromones is proposed based on mechanistic studies.

Iron(III) Chloride/Phenylsilane‐Mediated Cascade Reaction of Allyl Alcohols with Maleimides: Synthesis of Poly‐Substituted γ‐Butyrolactones

AbstractA iron‐catalyzed free radical cascade reaction of allyl alcohols with N‐substituted maleimides for accessing poly‐substituted γ‐butyrolactones has been developed. In this protocol, various allyl alcohols can open N‐substituted maleimide rings to form allyl ester intermediates, and the allyl ester intermediates can be converted into an allyl ester alkyl radicals and undergo intramolecular free radical addition cyclization to form a polysubstituted γ‐butyrolactones. In this protocol, spiro γ‐butyrolactone compounds can be also synthesized. Meanwhile, the strategy could be applied to further construct a fully substituted tetrahydrofuran. The reaction is not sensitive to oxygen or moisture and has been performed on gram‐scale.magnified image

Sequential Intermolecular Radical Addition and Reductive Radical Cyclization of Tyrosine and Phenylalanine Derivatives with Alkenes via Photoinduced Decarboxylation: Access to Ring-Constrained γ-Amino Acids.

Sequential radical addition to alkenes and reductive radical cyclization of phenylalanine and tyrosine derivatives via photoinduced decarboxylation furnished ring-constrained γ-amino acids under mild conditions. A variety of alkenes such as acrylamides and acrylic esters could be employed in the photoinduced radical cascade cyclization. The yields of the ring-constrained γ-amino acids are dependent on the electron-accepting ability and steric hindrance of the alkene used. The proposed sequential reaction can also be applied for direct tethering of dipeptides to yield unique ring-constrained tetrapeptides.

Ag-Mediated Radical Cyclization of 2-Alkynylthio(seleno)anisoles: Direct Synthesis of 3-Phosphinoylbenzothio(seleno)phenes

A new method for the direct synthesis of 3-phosphinoylbenzothio(seleno)phenes has been achieved through an Ag-mediated radical addition-cyclization of 2-alkynylthio(seleno)anisoles with secondary phosphine oxides in good yields under mild conditions. In this single reaction, benzenethiophene or benzeneselenophene skeleton, C(sp2)-P and C(sp2)-S bonds can be constructed with the cleavage of the C(sp3)-S bond, highlighting the efficiency and step-economics of this protocol.

Visible-light-induced tandem radical addition–cyclization of 2-aryl phenyl isocyanides catalysed by recyclable covalent organic frameworks

A heterogeneous visible-light-induced tandem radical addition–cyclization of isocyanides by photoactive covalent organic frameworks was developed, delivering diverse phenanthridines with high reaction efficiency and easy catalyst recyclability.

Glabralides A – C, three novel meroterpenoids from Sarcandra glabra

Glabralides A–C (1–3), three novel meroterpenoids including two unprecedented skeletons were isolated from the whole plants of Sarcandra glabra. Glabralide A (1) represented a unique skeleton of the chalcone-coupled monoterpenoid, bearing a bicyclo [2.2.2] octene core unit with five chiral centers. The structures were established by spectroscopic methods, including 2D NMR experiments, and the absolute configurations were determined using circular dichroic (CD) spectra. The plausible biogenetic pathway for 1 suggested that α-phellandrene was conjugated with chalcone by Diels-Alder cyclization, and for 3 implied that α-phellandrene and o-hydroxy phenylacetate cyclized by an uncommon radical addition and cationic cyclization.

Synthesis of ferrocene substituted dihydrofuran derivatives via manganese(III) acetate mediated radical addition-cyclization reactions

In this study, the manganese(III) acetate mediated radical addition-cyclization reactions of ferrocene substituted alkenes and active methylene compounds were carried out. The regio- and stereoselective radical cyclization reactions of (E)-styrylferrocene (1a) and active methylene compounds (2a-g) gave trans-5-ferrocenyl-4-phenyl-4,5-dihydrofuran compounds as the sole products. The reactions of 1-ferrocenyl-1-aryl(heteroaryl)ethenes (1b-e) and active methylene compounds (2a-f) via Mn(OAc)3 led to furan and benzofuran derivatives (10–33) in mid-good yields (up to 75%). Surprisingly, ferrocene substituted allylidene derivatives were obtained from the Mn(OAc)3 mediated reactions of 1-aryl-1-ferrocenylethene (1b-d) and 1,3-dimethylbarbituric acid (2g). The uses of ferrocene substituted alkenes in manganese(III) acetate mediated radical reactions is the first example in this field as far as we know.

Synthesis of Tribenzo[b,e,g]phosphindole Oxides via Radical Bicyclization Cascades of o-Arylalkynylanilines.

A new DTBP/Mg(NO3)2-mediated bicyclization cascade of o-arylalkynylanilines with secondary arylphosphine oxides has been developed, enabling dual C(sp2)-H functionalization along with the cleavage of the C-N bond. The combination between regioselective P-centered radical-triggered [3 + 2] cyclization and C-centered radical-induced cross-coupling in a one-pot manner delivered 27 examples of tribenzo[b,e,g]phosphindole oxides with generally high regioselectivity. A reasonable mechanism for forming such products involving radical addition-cyclization cascade is proposed.

Visible-Light-Induced Tandem Radical Addition-Cyclization of Alkenyl Aldehydes Leading to Indanones and Related Compounds.

Herein we describe a novel, visible light-induced tandem radical addition-cyclization of alkenyl aldehydes with α-bromocarbonyl compounds. A set of cyclic ketones, including indanones, cyclopentenones, 3,4-dihydronaphthalen-1(2H)-ones, and chroman-4-ones, are synthesized at room temperature with high efficiency and good functional group compatibility. It represents the first report on the catalytic 1,2-acylalkylation of unactivated alkenes.

Copper-Catalyzed Cascade Radical Addition–Cyclization Halogen Atom Transfer between Alkynes and Unsaturated α-Halogenocarbonyls

A Cu-catalyzed cascade radical addition/cyclization/halogen atom transfer between alkynes and α-halogeno-γ, δ-unsaturated carbonyl compounds for the synthesis of various substituted cyclopentenes is described. Since up to four Csp3–Csp2 bonds, two Csp3–Br bonds, and two carbocycles can be established in a single reaction, this 100% atom-efficient reaction exhibits the advantages of wide substrate scope, high functional group tolerance, and step-economics, and it offers an entry of the atom transfer radical addition/cyclization (tandem ATRA-ATRC) process to the synthesis of substituted cyclopentenes.

ChemInform Abstract: Oxidative Radical Addition—Cyclization of Sulfonyl Hydrazones with Simple Olefins by Binary Acid Catalysis.

AbstractThe scalable title reaction offers access to tetrahydropyridazines from N‐tosylhydrazones and styrenes, including 1,1‐disubstituted derivatives, as well as alkyl alkenes and cyclopentadiene.

Callviminols A-E, new terpenoid-conjugated phloroglucinols from the leaves of Callistemon viminalis

Callviminols A-E (1–5), five rare phloroglucinols bearing a framework embodying a hexahydrodibenzo[b,d]furan or 2-phenylcyclohexanol nucleus derived from a phloroglucinol-monoterpene adduct, were isolated from the leaves of Callistemon viminalis. Their structures were established via extensive spectroscopic measurements, with the absolute configuration of 5 determined by electronic circular dichroism (ECD) calculations. The plausible biogenetic pathway suggested that a unique oxidative radical addition and classic cationic cyclization were key biosynthetic steps.