Mechanisms and Kinetics of Radical Reaction of O（^1D,^3P） ＋ HCN System

The reaction of HCN with O（^1D, ^3p） radical has been investigated by density functional theory （DFT） and ab initio methods. The stationary points on the reaction paths （reactants, intermediates and products） were optimized at the （U）B3LYP/aug-cc-pVTZ level. Single-point calculations were performed at the （U）QCISD（T）/aug-cc-pVTZ level for the optimized structures and all the total energies were corrected by zero-point energy. It is shown that there exist three competing mechanisms of oxygen attacking nitrogen O→N, oxygen attacking carbon O→C and oxygen attacking hydrogen O→H. The rate constants were obtained via Eyring transition-state theory in the temperature range of 600～2000 K. The linear relationship between lnk and 1/T was presented. The results show that path 1 is the main reaction channel and the product of NCO ＋ H is predominant.

Recent Advances in Transition Metal-Catalyzed Asymmetric Radical Reactions

Control of enantioselectivity in radical reactions was a formidable challenge for organic chemists for decades. Thanks to the key role of transition metal complexes both in promoting and highly enantioselectively controlling sophisticated synthetic routes, great improvements in this filed have been achieved by merging transition-metal asymmetric catalysis with radical chemistry. Herein we provide a perspective of some of the most significant contributions in the field during the past decades. Accordingly, the major advances are classified based on different strategies for controlling stereoselectivity including： （1） chiral metal complex chelation, （2） chiral metal complex combined with radical species and reductive elimination, （3） chiral metal complex outer-sphere substitution by radical intermediate. Brief discussion of mechanism is presented whenever relevant.

Construction of axially chiral compounds via catalytic asymmetric radical reaction

The chemistry of axially chiral compounds has emerged as a subject of increasing interest due to their widespread presence in natural products,bioactive molecules,advanced materials,and chiral ligands/catalysts.On the other hand,catalytic asymmetric radical-based transformations provide a complementary platform for the construction of enantiomerically enriched molecules that are in growing demand in the chemical and pharmaceutical in-dustries.In recent years,considerable research efforts have been devoted to the development of catalytic asymmetric radical reactions for the construction of axially chiral compounds based on the unique reactivity modes of diverse radicals.In this review,we critically illustrate these recent achievements according to different radical precursors and catalytic activation modes.Wherever possible,special emphasis is also placed on the discussion of mechanistic features underlying these works and substrate scopes.This review should be of great interest to the experts in this area,but also serve as a helpful starting point for new researchers in this field.

Mn(Ⅲ)-mediated radical reaction of 2-isocyano-6-alkenyl(alkynyl)benzonitriles with arylboronic acids:Synthesis of pyrroloisoquinoline derivatives

A Mn(Ⅲ) mediated radical reaction of new designed multi-functionalized 2-isocyano-6-alkenyl(alkynyl)benzonitriles with arylboronic acids has been developed.This reaction provides a method for the synthesis of pyrroloisoquinoline derivatives through the formation of two C-C bonds and one C-N bond via radical cascade cyclization in one step.

Liver Nuclear Activation of Carbon Tetrachloride or Bromotrichloromethane to Trichloromethyl and Trichloromethylperoxyl Free Radicals.Their Reactions With Lipids and Proteins

The formation of·CCl3 radicals in liver nuclei was suggested by spin trapping of them with N-t-butyl-α-phenylnitrone followed by GC/MS detection of the resulting adduct. Comparison of its formation in microsomal biotransformation of CCl4 was made. In aerobic nuclear activation mixtures containing NADPH and CCl4, significant decrease in the arachidonic acid content of nuclear lipids was observed (27. 8%, compared to control), the intensity of this decrease was lower than that occurring in the corresponding microsomal incubation mixtures (29.1%). Significant decreases in arachidonic acid content of nuclear and endoplasmic reticulum lipids were also observed in animals at 6 hours of poisoning with the haloalkane. During aerobic nuclear metabolism of CCl4 or CBrCl3, cholesterol oxidation products were detected: a ketocholesterol, an epoxide like structure and 7-ketocholesterol. Nuclear protein carbonyl formation was not promoted during nuclear CCl4 biotransformation. NADPH by itself may lead to protein carbonyl formation during prolonged periods of incubation. CBrCl3 in contrast, led to decreased protein carbonyl formation. No increase in nuclear protein carbonyl formation was observed in CCl4 intoxicated animals during periods of time between 1 to 6 hours after treatment. The results indicate that during nuclear biotransformation of CCl4 or CBrCl3 reactive free radicals, PUFA degradation, reactive aldehydes and cholesterol oxidation products are formed, nearby DNA and regulatory proteins.

Asymmetric Total Synthesis of (+)-21-epi-Eburnamonine Via a Photocatalytic Radical Cascade Reaction

An asymmetric total synthesis of(+)-21-epi-eburnamonine has been achieved.Key features of the synthesis include a visible-light photocatalytic intra-/intramolecular radical cascade reaction to assemble the tetracyclic ABCD ring system,and a highly diastereoselective Johnson-Claisen rearrangement to establish the C20 all-carbon quaternary stereocenter.

THE RADICAL NUCLEOPHILIC SUBSTITUTION REACTION OF HETEROCYCLIC KETENE AMINALS WITH 2,4-DINITROHALOBENZENES

The anion of heterocyclic ketene aminals reacted with 2,4-dini- tro-halobenzenes to give an arylated product through the radical nucleo- philic substitution confirmed by ESR spectroscopy,ESR-spin trapping techni- que,and depression of the reaction rate by the addition of inhibitor.

Kinetics for the reaction of hydroxyl radicals with CH_3Br and its implications in the atmosphere

ＫｉｎｅｔｉｃｓｆｏｒｔｈｅｒｅａｃｔｉｏｎｏｆｈｙｄｒｏｘｙｌｒａｄｉｃａｌｓｗｉｔｈＣＨ３ＢｒａｎｄｉｔｓｉｍｐｌｉｃａｔｉｏｎｓｉｎｔｈｅａｔｍｏｓｐｈｅｒｅＺｈａｎｇＤｅｑｉａｎｇ，ＺｈｏｎｇＪｉｎｘｉａｎＲｅｓｅａｒｃｈＣｅｎｔｅｒｆｏ...

MCSCF STUDIES ON THE IRC AND REACTION RATE CONSTANTS FOR THE DEHYDROGENATION REACTION OF VINYL RADICAL

The transition state(TS) and Intrinsic Reaction Coordinate (IRC) for the titled reaction were traced by means of MCSCF/6-31G (210 configurations). The reaction activation energy of this reaction is 140.2KJ/mol. The reaction rate constants of five temperetures were calculated by CVT involving the tunneling effects.

Revelation of bimolecular tautomerization induced by the concerted and radical interactions in lignin pyrolysis

Bimolecular interactions play crucial roles in lignin pyrolysis.The tautomerization of key intermediates has a significant impact on the formation of stable products,whereas bimolecular tautomerization has been rarely clarified.In the present work,the bimolecular tautomerization mechanism induced by both concerted and radical interactions was proposed and carefully confirmed.A characteristicβ-O-4 lignin dimer,2-phenoxy-1-phenylethanol(α-OH-PPE),was used as the model compound to reveal two representative keto-phenol and enol-keto tautomerism mechanisms,based on theoretical calculations combined with pyrolysis experiments.The results indicate that the unimolecular tautomerism as the rate-determining step limits product generation,due to fairly high energy barriers.While the free hydroxy compounds and radicals derived from initial pyrolysis can further initiate bimolecular tautomerism reactions through the one-step concerted hydroxyl-assisted hydrogen transfer(hydroxylAHT)and two-step radical hydrogen abstraction interactions,respectively.By alleviating and even avoiding the large ring tension of tautomerism,the unstable tautomers(2,4-cyclohexadienone and1-hydroxy styrene)can be rapidly tautomerized into stable phenol and acetophenone with the help of intermolecular interaction.Benefitting from the significant advantage of retro-ene fragmentation in breaking theβ-O-4 bond to form tautomers,a large amount of stable phenolic and ketone products can be generated following bimolecular tautomerization in the pyrolysis ofβ-O-4 linked lignin.

Theoretical Study on the Reaction Mechanism of F_2+2HBr = 2HF+Br_2

The gas phase reaction mechanism of F2 ＋ 2HBr = 2HF ＋ Br2 has been investigated by （U）MP2 at 6-311G＊＊ level, and a series of four-center and three-center transition states have been obtained. The reaction mechanism was achieved by comparing the activation energy of seven reaction paths, i.e. the dissociation energy of F2 is less than the activation energy of the bimolecular elementary reaction F2 ＋ HBr → HF ＋ BrF. Thus it is theoretically proved that the title reaction occurs more easily in the free radical reaction with three medium steps.

Recent Developments in Copper(Ⅰ)-Catalyzed Enantioselective Alkynylation Reactions via a Radical Process

Alkynes are one of the most significant functional groups in organic chemistry and great efforts have been made to explore efficient approach for the construction of chiral alkynes.The asymmetric C(sp^(3))–C(sp)cross-coupling provides a significant complementary strategy through radical-initiated process.However,the stereocontrol of highly reactive and unstable radical intermediate has been a challenge for decades.To address this problem,a variety of chiral ligands are developed for initiating the reaction and achieving enantiocontrol of alkyl radicals.This review summarizes recent developments in copper-catalyzed enantioselective alkynylation of prochiral alkyl radicals and their brief mechanistic studies.

Visible Light-Induced[3+2]Annulation Reaction of Alkenes with Vinyl Azides:Direct Synthesis of Functionalized Pyrroles

A photocatalytic[3+2]annulation of alkenes with vinyl azides was developed under irradiation by visible light in the presence of organic dye photocatalysts.Broad substrate scope and high functional group tolerance were demonstrated by more than 50 examples.The reaction provides a novel and efficient method for the synthesis of polyfunctionalized pyrroles under very mild metal-free conditions without other additives.

Photocatalytic Site-Selective Cascade Radical Addition of Biaryl Ynones for the Construction of Spiro-and Fused Carbon Rings

Functionalized free radical addition/cyclization reactions represent an efficient way for introducing new functionality or coupling fragments to molecules.Ynones are good regional selectivity radical acceptors in organic synthesis,and many of bio-relevant cyclic compounds could be easily obtained by direct radical cyclization reaction.Here,we report a photocatalytic cascade radical addition of biaryl ynones,for the divergent synthesis of privileged carbon cycles.Additionally,further transformation of the multi-functional group product into a variety of other derivatives demonstrates the synthetic value of this developed method.

Theoretical insights of the pharmaceutical compound fluoxetine in water:Role in direct photolysis and indirect photolysis by free radicals

The frequent detection of pharmaceutical compounds in the environment has led to a growing awareness,which may pose a major threat to the aquatic environment.In this study,photodegradation(direct and indirect photolysis)of two different dissociation states of fluoxetine(FLU)was investigated in water,mainly including the determination of photolytic transition states and products,and the mechanisms of indirect photodegradation with·OH,CO_(3)^(*-)and NO_(3)^(*).The main direct photolysis pathways are defluorination and C–C bond cleavage.In addition,the indirect photodegradation of FLU in water is mainly through the reactions with·OH and NO_(3)^(*),and the photodegradation reaction with CO_(3)^(*-)is relatively difficult to occur in the water environment.Our results provide a theoretical basis for understanding the phototransformation process of FLU in the water environment and assessing its potential risk.

An Isolable Phosphinogermylyne as a Synthon of One-Coordinate GeⅠRadical

Reduction of chlorogermylene MsFluindtBu-GeCl 1 with potassium graphite(KC8)afforded putative germylyne radical MsFluindtBu-Ge 2 as confirmed by electron paramagnetic resonance(EPR)spectroscopy.However,it slowly decayed via C—H bond activation at the fluorenyl moiety to yield a bis(germylene)3 at room temperature.By using a Lewis base to stabilize the unoccupied p orbital at the GeⅠradical center,acyclic two-coordinate GeⅠradicals MsFluindtBu-Ge(IMe4)4(IMe4=1,3,4,5-tetramethyl-imidazolin-2-ylidene),MsFluindtBu-Ge(IiPr)5(IiPr=1,3-diisopropyl-4,5-dimethyl-imidazolin-2-ylidene),MsFluindtBu-Ge(PMe3)6 were isolated in crystalline forms.The unpaired electron in 4-6 mainly resides at the Ge 4p orbital as revealed by EPR spectroscopic studies and theoretical calculations.Interestingly,facile ligand exchange of PMe3 in 6 with IMe4 and IiPr was observed to afford 4 and 5,respectively.Moreover,phosphinogermylyne 6 reacted with PhEEPh(E=S,Se),4-tetrabutylphenylacetylene(Ar'CCH),[CpMo(CO)3]2 and nBu3SnH to furnish germylenes MsFluindtBu-GeEPh(E=S 7,Se 8),MsFluindtBu-GeCH=CHAr'9,a germylyne complex MsFluindtBu-Ge≡Mo(CO)2Cp 10 and a Ge(Ⅳ)compound MsFluindtBu-GeH2SnnBu311,respectively.The reactivity studies demonstrate that 6 can act as a synthon of one-coordinate germylyne radical attributing to labile coordination of trimethylphosphine.

Recent Advances in C-F Bond Formation from Carbon-Centered Radicals

Construction of C-F bonds is a direct and efficient method for introducing fluorine into pharmaceuticals,agrochemicals,and materials.Strategies such as nucleophilic,electrophilic,radical,and transition-metal catalyzed fluorination have been developed to meet the demand of diverse C-F bond formation.Among them,radical fluorination has been witnessed with substantial advancement in a recent decade.Herein,we reviewed methods for formation of C-F bonds with carbon-centered radicals as key intermediates,especially in recent five years.We introduce in the paper with different fluorinating reagents,strategies for radical generation,and application in late-stage functionalization and synthesis of PET tracers.We also indicate the current limitations and propose the direction of the field for the future development.

An Olefinic 1,2-α-Boryl Migration Enables 1,2-Bis(boronic esters)via Radical-Polar Crossover Reaction

A radical-induced 1,2-α-boryl migration through radical polar crossover reactions has been described.In this work,in situ formed vinyldiboron“ate”complexes from alkenyl Grignard reagent and diborylalkanes react with commercial radical precursors under light initiation.This three-component process enables diborylation of alkene.This protocol features high atom economy,a broad substrate scope as well as good functional group toleration with mild conditions.

Polyaniline-supported tungsten-catalyzed oxidative deoximation reaction with high catalyst turnover number

Polyaniline-supported tungsten(W@PANI)was easily prepared by immersing polyaniline(PANI)in the aqueous solution of Na2WO4.It was found to be an efficient catalyst for oxidative deoximation reaction,the very important transformation for pharmaceutical industry.Besides the green features,the method employed very few of catalytic tungsten(0.048 mol%vs.oxime substrates),resulting in the high turnover numbers(TONs)of the catalyst(ca.103 mol/mol)and the low metal residues in product(<0.1 ppm).The reaction is applicable for a variety of substrates,including those containing heterocycles,which are key intermediates in medicine synthesis.It has also been successfully magnified to kilogram scale production to afford the desired carbonyl products smoothly.