Thianthrene Cation Radical Research Articles

Thianthrene Radical Cation as a TransientSETMediator: Photoinduced Thiocyanation and Selenocyanation of Arylthianthrenium Salts†

Comprehensive SummaryA novel transient SET mediator approach has been developed for the photoinduced radical‐radical cross coupling reaction. Using thein‐situgenerated thianthrene radical cation as the transient SET mediator, the thiocyanation and selenocyanation of aryl thianthrenium salts have been realized under the mild conditions without the need for photocatalyst or single electron donor. In comparison with the photocatalyst enabled process, the protocol features mild conditions, simple manipulation, a broad substrate scope, excellent functional group and heterocycle tolerance. Due to the feasible accessibility of aryl thianthrenium salts, this method has also been applied in the efficient synthesis of a bioactive molecule, and the late‐stage functionalization of complex arenes.

Hydrogen Atom Transfer for C(sp3)−H Functionalization Enabled by Photoredox/Thianthrene/Methanol Synergistic Catalysis

AbstractA synergetic catalytic system of organophotocatalyst 4CzIPN, thianthrene, and methanol was developed for visible‐light‐induced Giese reactions of various alkanes and alkenes, upon using alkoxy radicals as hydrogen atom transfer reagents. The reaction can be performed under mild conditions to provide the alkylated products in moderate to excellent yields, avoiding the use of any strong oxidants and transition metal reagents. Different from the known LMCT and PCET processes, the key to success of this approach is the in situ thianthrenation of methanol by thianthrene radical cation to trigger the generation of methoxy radical.

One Electron Changes Everything: Synthesis, Characterization, and Reactivity Studies of [Re(NCCH3)6]3.

Oxidation of [Re(NCCH3)6]2+ with the thianthrene radical cation results in the formation of [Re(NCCH3)6]3+, one of the very rare cases of a fully solvated +3 complex. It was fully characterized by spectroscopy and X-ray structure analysis. In contrast to its reduced analogue, [Re(NCCH3)6]3+ exhibits a much faster CH3CN exchange. Hence, substitution reactions proceed at 20 °C within minutes. Its potential as a versatile precursor for ReIII chemistry was examined with a series of substitution reactions. The more lipophilic analogue [Re(NCPh)6]3+ was synthesized by nitrile exchange in benzonitrile (NCPh). The Re(II) analogue of [Re(NCPh)6]3+, [Re(NCPh)6]2+, forms by AgI-mediated oxidation of in situ formed [Re(η6-C6H6)(NCPh3)3]+ in NCPh. The same synthetic strategy is feasible for the synthesis of [Re(NCCH3)6]2+ as well. [Re(NCCH3)6]3+ reacts with 1,4,7-trithiacyclononane (C6H12S3) to yield sevenfold-coordinated [Re(κ3-C6H12S3)2(NCCH3)]3+. The reaction of [Re(NCCH3)6]3+ with 1 equiv of (NBu4)X produces the ReIII monohalide complexes [ReX(NCCH3)5]2+ (X = Cl, Br, I). Mixed ReIII dihalides (trans-[ReXY(NCCH3)4]+) were obtained by treating [ReX(NCCH3)5]2+ with a second equivalent of (NBu4)Y (if X = Cl, Y = Br, I; if X = Br, Y = I). Because of this fast CH3CN exchange, [Re(NCCH3)6]3+ is a very suitable precursor for new ReIII complexes.

Photochemical (Hetero-)Arylation of Aryl Sulfonium Salts.

The construction of (hetero)biaryls, which are ubiquitous scaffolds among medical substances, functional materials, and agrochemicals, constitutes a key application of cross-coupling methods. However, these usually require multiple synthetic steps. Herein, we report a simple photoinduced and catalyst-free C–H/C–H (hetero)arylation cross-coupling through aryl thianthrenium salts, which are formed site-selectively by direct C–H functionalization. The key to this approach is the UV-light, which can disrupt the C–S bond to form thianthrene radical cations and aryl radicals.

Redox Switchable Thianthrene Cavitands

A redox activated vase-to-kite conformational change is reported for a new resorcinarene-based cavitand appended with four quinoxaline-fused thianthrene units. In its neutral state, the thianthrene-containing cavitand was shown by 1H NMR to adopt a closed vase conformation. Upon oxidation the electrostatic repulsion among the thianthrene radical cations promotes a kite conformation in the thianthrene-containing cavitand. The addition of acid produced a shoulder feature below 300 nm in the cavitand’s UV-Vis spectrum that we have assigned to the vase-to-kite conformation change. UV-Vis spectroelectrochemical studies of the cavitand revealed a development of a similar shoulder peak consistent with the oxidation-induced vase-to-kite conformation change. To support that the shoulder peak is diagnostic for a vase-to-kite conformation change, a model molecule constituting a single quinoxaline wall of the cavitand was synthesized and studied. As expected UV-Vis spectroelectrochemical studies of the cavitand arm did not display a shoulder peak below 300 nm. The oxidation-induced vase-to-kite conformation is further confirmed by the distinctive upfield shift in 1H chemical shift of the methine signal.

ChemInform Abstract: Synthesis of 2‐Styrylbenzoxazole Derivatives by the Reaction of Styrylphenolic Schiff Bases with Thianthrene Cation Radical.

AbstractThe products are obtained in much lower yields in the absence of 2,6‐di‐tert‐butyl‐4‐methylpyridine.

Radical Polymerization of Vinyl Monomers to Poly(vinyl)s havingnBu3Sn end Groups with Biological Activity

<TEX>$Bu_3Sn$</TEX>-endded poly(vinyl)s with biological activity were obtained by the radical polymerization of vinyl monomers using thianthrene cation radical/<TEX>$^nBu_3H$</TEX>. Thianthrene cation and stannyl radicals promoted the homopolymerization and copolymerization of styrene and ethyl vinyl ether having number average molecular weights of 2000-3100. Tributyltin hydride functions as a chain transfer agent. Such polymereization by cationic thianthrene and stannyl radicals could provide some clues for the biological reaction in living animals. Plausible polymerization mechanisms were suggested.

Synthesis of 2-Styrylbenzoxazole Derivatives by the Reaction of Styrylphenolic Schiff Bases with Thianthrene Cation Radical

A simple and fast preparative method of 2-styrylbenzoxazoles by oxidative intramolecular cyclization of styrylphenolic Schiff bases with thianthrene cation (Th+.ClO4−) is described. The oxidative cyclization of Schiff bases in the presence of 2,6-di-tert-butyl-4-methylpyridine (DTBMP) gives 2-styrylbenzoxazole derivatives in better yields than those in the absence of DTBMP.

Polymerization of Vinyl Monomers Initiated by Thianthrene Cation Radical with Potential Biological Activity

Polymerization of vinyl monomers is promoted by thianthrene cation radical as a part of our research concerning the reactions of various agents with readily isolable, yet highly reactive species and elucidate the biological activity. Thianthrene cation radical initiated the homopolymerization and copolymerization of styrene and ethyl vinyl ether. The polymerization yields decreased as the concentration of phenylacetylene or diphenylethylene increased. Such polymereization by cationic thianthrene radical could provide some clues for the reaction in living animals. Comments on possible polymerization mechanisms were suggested.

ChemInform Abstract: Reactions of Phenols with Thianthrene Cation Radical.

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Electron Transfer−Oxygen Transfer Oxygenation of Sulfides Catalyzed by the H5PV2Mo10O40 Polyoxometalate

The oxygenation of sulfides to the corresponding sulfoxides catalyzed by H(5)PV(2)Mo(10)O(40) and other acidic vanadomolybdates has been shown to proceed by a low-temperature electron transfer-oxygen transfer (ET-OT) mechanism. First, a sulfide reacts with H(5)PV(2)Mo(10)O(40) to yield a cation radical-reduced polyoxometalate ion pair, R(2)(+*),H(5)PV(IV)V(V)Mo(10)O(40), that was identified by UV-vis spectroscopy (absorptions at 650 and 887 nm for PhSMe(+*) and H(5)PV(IV)V(V)Mo(10)O(40)) and EPR spectroscopy (quintet at g = 2.0079, A = 1.34 G for the thianthrene cation radical and the typical eight-line spectrum for V(IV)). Next, a precipitate is formed that shows by IR the incipient formation of the sulfoxide and by EPR a VO(2+) moiety supported on the polyoxometalate. Dissolution of this precipitate releases the sulfoxide product. ET-OT oxidation of diethylsulfide yielded crystals containing [V(O)(OSEt(2))(x)(solv)(5-x)](2+) cations and polyoxometalate anions. Under aerobic conditions, catalytic cycles can be realized with formation of mostly sulfoxide (90%) but also some disulfide (10%) via carbon-sulfide bond cleavage.

The First Example of Cation Radical Induced Ether Cleavage of Benzyl Phenyl Ether

In a continuation of our work with benzyl phenyl ether (1), in acetonitrile at room temperature, it was found to undergo oxidative C-O bond cleavage by the thianthrene cation radical (Th+•ClO4‒). As far as the authors are aware, reactions of ether with cation radicals have not been reported, and as such, they offer the first examples of cation radical-induced ether cleavage. Generally, ethers react only reluctantly with bases, reducing agents and oxidizing agents. The C-O cleavage of benzyl phenyl ether typically occurs by heating with one equivalent of acid, through a SN1 pathway given the relative stability of the benzyl cation being formed; this is followed by C-O cleavage. It has been found that 1 reacts quantitatively with Th at a 1:2 (1:Th) stoichiometry to give quinonoids (3), N-benzylacetamide (4), and thianthrene (Th). The simplest representation of the reaction is given in Scheme 1. The products yielded were determined by quantitative GC and GC/MS analyses. NBenzylacetamide (4) was isolated in a yield of 87.4%, 3 (100%), Th (96.4%), phenol (1.01%), and trace amounts of ThO. A mechanism that fits the formation of such products involves the initial complexation of Th with 1 (eq 5) to produce a species more easily oxidized than Th, where electron transfer (eq 6) produces a thianthrene dication-benzyl phenyl ether complex (Th-1) that undergoes a rate-determining bond formation with expulsion of a proton (eq 7) to product 2. Benzyl cations are subsequently formed by SN1 loss of 3 from 2. Benzyl cations then react with the acetonitrile solvent, to give a Ritter-type intermediate (C6H5CH2N=CMe), which then reacts with water during work-up to give 4.

Benzyl Cation Formation from the Reaction of Benzyl Alcohol with Thianthrene Cation Radical

) from the benzyl cation, isolated in a yield of 90%, Th (100%) and ThO (90%) were formed quantitatively, according to the results of the formation of an alkoxysulfonium ion in eq 2 (R = benzyl). Contrary to Yueh and Shine's re port, in our reaction, no trace amounts of dibenzyl ether was obtained. 2 Th

Thianthrene Radical Cation Hexafluorophosphate

In the presence of [NBu4][PF6] as the electrolyte, thianthrene (TA) is transformed by electrochemical oxidation to thianthrenium hexafluorophosphate containing the TA•+ radical cation. The reactions were performed in CH2Cl2, H3CCN, and liquid SO2 as solvents. In CH2Cl2, TA[PF6] is sparingly soluble and is deposited directly in crystalline form on the platinum electrode. In H3CCN and liquid SO2, TA[PF6] is highly soluble and gives dark blue solutions from which it can be crystallized upon concentration of the solutions. The air sensitive crystals are black with bronze metallic luster. They belong to the monoclinic system (C2/m, a = 12.4345(8), b = 10.5318(6), c = 11.1303(7) Å , β = 112.565(3)◦) and are built up of almost planar TA•+ cations and octahedral [PF6]− anions. The F atoms of the anions are disordered over two positions. The radical cations are associated to form dimeric units (TA•+)2 with the planar molecules stacked with two weak S· · ·S bonds (3.06 Å ). In the crystal these dimers are separated by the [PF6]− anions. Electrical conductivity measurements show TA[PF6] to be a small-gap semiconductor. Conductivity is low at r. t. but reaches 2.5 · 10−5 S m−1 at 110 °C, the activation energy in the high-temperature region amounts to 1.2 eV. Periodic quantum-chemical calculations at hybrid density-functional level predict a strong coupling between neighboring (TA•+) spin centers, resulting in a singlet ground state. The calculated band gaps of both singlet (1.5 eV) and triplet (0.9 eV) states are small, consistent with the measured conductivity

Reactions of thianthrene cation radical tetrafluoroborate with aldehydes: formation of α-(5-thianthreniumyl)aldehyde tetrafluoroborates – a facile synthesis of α-ketols through Lobry de Bruyn–van Ekenstein rearrangement

Reactions of thianthrene cation radical tetrafluoroborate with aldehydes, namely, butanal, pentanal, hexanal, heptanal, octanal, nononal, decanal, undecanal, dodecanal, tridecanal, and 3-phenylpropanal, led to the formation of α -(5-thianthreniumyl)aldehyde tetrafluoroborates (13a–k). Adducts (13a–k) are unstable and are converted to the corresponding hydrates (14a–k) when exposed to moisture or by deliberate addition of water to their solutions. Adducts (13a–k) and their hydrates (14a–k) were characterized with 1H, 13C, and DEPT NMR spectroscopy. Interestingly, when solutions of adducts (13a–k) in acetonitrile were stirred with activated alumina, facile conversion to α -ketols (15a–k) occurred. It is proposed that the formation of α -ketols (15a–k) occurred through the Lobry de Bruyn–van Ekenstein rearrangement from the initially formed α -hydroxyaldehydes. α -Ketols 15a–j were isolated in good yield and their identities were confirmed with NMR spectroscopy.

Reaction of Azodioxide with Thianthrene Cation Radical

We recently reported on the thianthrene cation radical perchlorate (Th·ClO4) induced oxidative decomposition of carbonates (eq 1), carbamates (eq 2), azodicarboxylate (eq 3), dicarbonate (eq 4), peroxides (eq 5), and disulfide (eq 6) where R in equations is tert-butyl. In each of these reactions, electron-transfer-mediated C,N, C,O or C,S bond cleavage was found. Substantial bond weakening was shown to accompany the tert-butyl cation due to the electron loss from these substrates. In a continuation of our work on N,N'-dioxoazobis(2methyl-2-propane) (1) in acetonitrile solution at room temperature, C,N and N,O cleavages, followed by addition of Th·ClO4 to azodioxide, 1, was found to give thianthrene oxide (ThO) and N-t-butylacetamide (3), with evolution of nitrogen gas. Reactions of Th·ClO4 with anions, such as nitrite and nitrate ions, have been reported, but its reactions with molecules with an abnormal number of bonds have not been documented. This work affords the first example of the addition of a cation radical to formal negatively charged oxygen within a neutral molecule. Reactions of nitrite and nitrate ions with Th·ClO4 were found to give thianthrene 5-oxide (ThO) quantitatively (Scheme 1). Reactions with O-labeled nitrite and nitrate ions showed that the oxygen in ThO came from the nitrite and nitrate ions respectively. In the present study, as with the other oxidative decomposition, the major products from the reaction of 1 with Th·ClO4 are also characteristic of tert-butyl cations, which imply carbocationic chemistry is predominantly observed from a nitrosoalkane dimer. The products obtained were N-tbutylacetamide (3), ThO and N2 as determined by quantitative GC and GC/MS analyses. N-t-butylacetamide (3) from the tert-butyl cation, which was isolated in a yield of 91%, and ThO (76%) was obtained by oxygen transfer from 1. Without doubt, 3 arose from hydration, during workup, of a Ritter-type intermediate (Me3CN=CMe) from the reaction of Me3C with the MeCN solvent. Accordingly, all reactions were carried out with a 2:1 stoichiometry of the cation radical and 1. Generally, in the reaction of thianthrene cation radical perchlorate, ThO is obtained as a side product from the hydrolysis of Th·ClO4 by water, either adventitiously in the solvent or added during workup. However, in this

Some Reactions of the Thianthrene Cation Radical: Products and Mechanism of Their Formation

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

An overview of some reactions of thianthrene cation radical. Products and mechanisms of their formation

A comprehensive review of recent chemistry of thianthrene cation radical is presented. Particularly, products and mechanisms of their formation from reactions with azo compounds, hydrazones, oximes, sulfonamides, alcohols, phenols, alkenes, alkynes and organometallics are discussed. Also, reactions of 5-(substituted)thianthrenium salts are reviewed.

Reactions of thianthrene cation radical with acyclic α, ω-diols: Formation of monoadducts and bisadducts. Intramolecular cyclization of monoadducts to cyclic ethers

Reactions of thianthrene cation radical tetrafluoroborate () with α, ω-diols, HO(CH2) n OH (4b–g, n=5, 6, 8–10, 12), at the molar ratio Th•+:4 2/1 in MeCN containing 2,6-di-tert-butyl-4-methylpyridine (DTBMP) led to formation of bisadducts, α, ω-di(5-thianthreniumoxy)alkane ditetrafluoroborates (7b–g). Reactions with 4b,c gave also the cyclic ethers 6b,c by intramolecular cyclization. Preparation of the bisadduct (7a) from 1,4-butanediol (4a) was achieved only in the absence of DTBMP, in low yield. The major product was tetrahydrofuran (THF, 6a). Reactions of with 4b–g in the molar ratio 1/6, carried out in MeCN without DTBMP, led to the formation of monoadducts, α-hydroxy-ω-(5-thianthreniumoxy)alkane tetrafluoroborates (5b–g). Reactions with 4b,c led again also to cyclic ethers 6b,c. Cyclization of adducts to ethers (6b,c) was confirmed with the isolated monoadducts (5b,c). Attempts to prepare a monoadduct (5a) from 4a were unsuccessful; only THF (6a) was obtained. 5b–g and 7a–g were characterized with 1H and 13C NMR spectroscopy. Reactions of 7b,c with basic alumina resulted in formation of 4b,c rather than in elimination of thianthrene oxide and formation of linear dienes.

Reaction of Thianthrene and Phenoxathiin Cation Radicals with 2,3-Dimethyl-2-butene. Chemical and Electrochemical Studies

Thianthrene cation radical tetrafluoroborate (Th*+ BF4-) has been found to add to 2,3-dimethyl-2-butene (DMB) at 0 degrees C and -15 degrees C. The adduct, 2,3-dimethyl-2,3-(5,10-thianthreniumdiyl)butane ditetrafluoroborate (12), was isolated at -15 degrees C, and its 1H NMR spectrum was recorded at that temperature. The adduct was stable in CD3CN solution at -15 degrees C but decomposed slowly at 0 degrees C and quickly at 23 degrees C, forming the salt of 2,4,4,5,5-pentamethyl-2-oxazoline (8) with loss of thianthrene (Th). These results explain why earlier attempts to prepare 12 and detect its formation at room temperature with NMR spectroscopy were not successful. Reaction of Th*+ with DMB was followed with cyclic voltammetry and was found to exhibit redox catalysis in which Th was regenerated. With the faster scanning techniques of cyclic voltammetry, the formation of 12 was detectable, with a reduction potential of about -1.0 V at 25 degrees C and 3 degrees C. The observed reduction potential was in harmony with reduction potentials of a number of other, stable monoadducts. Thus, the redox catalysis involved the rapid formation of 12 and its rapid decomposition into 8 and Th, the newly formed Th being responsible for the observed enhanced oxidation currents. In contrast, 8 appears to be formed directly by oxidation of DMB by PO*+PF6-.