Extrusion Of Sulfur Dioxide Research Articles

Tandem Diels-Alder and retro-ene reactions of 1-sulfenyl- and 1-sulfonyl-1,3-dienes as a traceless route to cyclohexenes.

A pericyclic approach for the synthesis of six-membered ring structures is described. The method employs 1,3-dienes with a 1-sulfur substituent in a tandem sequence of Diels-Alder and retro-ene reactions. In this pairing of [4 + 2] cycloaddition and 1,5-sigmatropic rearrangement, 1-sulfenyl-1,3-dienes engage in Diels-Alder reactions with electron-deficient dienophiles. Subsequently, the sulfenyl group of the cycloadducts is oxidized and unmasked to form allylic sulfinic acids, which undergo sterospecific reductive transposition via sulfur dioxide extrusion. The sequence can also include an inverse electron demand Diels-Alder reaction by using a 1-sulfonyl-1,3-diene. This combination of two pericyclic events offers novel stereocontrolled access to cyclohexenes that are inaccessible via a direct [4 + 2] cycloaddition route.

Palladium and TEMPO as Co‐Catalysts in a Desulfinative Homocoupling Reaction

AbstractA range of aryl sulfinates can be oxidatively dimerized to generate substituted biphenyls with concomitant extrusion of sulfur dioxide with a palladium catalyst. Catalytic amounts of TEMPO and excess oxygen are utilized as oxidants to regenerate the palladium catalyst.

ChemInform Abstract: A Synthesis of (1E,3E)‐TMS Dienes from Keto‐Xanthates via Chugaev‐Type Elimination.

An efficient route leading to exclusively (1E,3E)-TMS dienes is described. Radical xanthate addition of keto-xanthates to vinyltrimethylsilane followed by one-pot Chugaev elimination/cyclization and in situ oxidation with m-CPBA afforded the corresponding TMS 2-sulfolenes. Isomerization to 3-sulfolenes by the action of DBU with the extrusion of sulfur dioxide in refluxing toluene gave the titled (1E,3E)-TMS dienes.

A Synthesis of (1E,3E)-TMS Dienes from Keto-Xanthates via Chugaev-Type Elimination

An efficient route leading to exclusively (1E,3E)-TMS dienes is described. Radical xanthate addition of keto-xanthates to vinyltrimethylsilane followed by one-pot Chugaev elimination/cyclization and in situ oxidation with m-CPBA afforded the corresponding TMS 2-sulfolenes. Isomerization to 3-sulfolenes by the action of DBU with the extrusion of sulfur dioxide in refluxing toluene gave the titled (1E,3E)-TMS dienes.

Aqueous Oxidation of Sulfonamide Antibiotics: Aromatic Nucleophilic Substitution of an Aniline Radical Cation

Sulfonamide antibiotics are an important class of organic micropollutants in the aquatic environment. For several, sulfur dioxide extrusion products have been previously reported upon photochemical or dark oxidation. Using quantum chemical modeling calculations and transient absorption spectroscopy, it is shown that single-electron oxidation from sulfadiazine produces the corresponding aniline radical cation. Density functional theory calculations indicate that this intermediate can exist in four protonation states. One species exhibits a low barrier for an intramolecular nucleophilic attack at the para position of the oxidized aniline ring, in which a pyrimidine nitrogen acts as a nucleophile. This attack can lead to a rearranged structure, which exhibits the same connectivity as the SO2 -extruded oxidation product that was previously observed in the aquatic environment and characterized by NMR spectroscopy. We report a detailed reaction mechanism for this intramolecular aromatic nucleophilic substitution, and we discuss the possibility of this reaction pathway for other sulfonamide drugs.

Conformational Landscape, Photochemistry, and Infrared Spectra of Sulfanilamide

A combined matrix isolation FTIR and theoretical DFT(B3LYP)/6-311++G(3df,3pd) study of sulfanilamide (SA) was performed. The full conformational search on the potential energy surface of the compound allowed the identification of four different minima, all of them bearing the sulfamide nitrogen atom placed in the perpendicular orientation relatively to the aromatic ring and differing from each other in the orientation of the hydrogen atoms connected to the two nitrogen atoms of the molecule. All conformers were predicted to be significantly populated in the gas phase (at 100 °C, their relative populations were estimated as being 1:0.9:0.3:0.2). However, in agreement with the theoretically calculated low-energy barriers for conformational isomerization, in the low-temperature matrices, only the most stable conformer could be observed, with the remaining forms being converted into this form during matrix deposition (conformational cooling). The unimolecular photochemistry of matrix-isolated SA (in both argon and xenon) was also investigated. Upon broadband UV irradiation (λ > 215 nm), two photofragmentation pathways were observed: the prevalent pathway (A), leading to extrusion of sulfur dioxide and simultaneous formation of benzene-1,4-diamine, which then converts to 2,5-cyclohexadiene-1,4-diimine, and the minor pathway (B), conducting an γ-cleavage plus [1,3] H-atom migration from the sulfamide group to the aromatic ring, which leads to formation of iminosulfane dioxide and aniline, the latter undergoing subsequent phototransformation into cyclohexa-2,5-dien-1-imine. Finally, the crystalline polymorph of SA resulting from warming (265 K) the amorphous solid obtained from fast cooling of the vapor of the compound onto the cold (13 K) substrate of the cryostat was identified spectroscopically, and found to be the γ-crystalline phase, the one exhibiting in average longer H-bonds and an infrared spectrum resembling more that of the low temperature SA glass. Full assignment of the infrared spectra of this crystalline variety as well as of those of the β-polymorph room temperature crystalline sample and low temperature amorphous state was undertaken with help of theoretical results obtained for the crystallographically relevant dimer of SA.

ChemInform Abstract: Preparation and Reduction of Hexahydro(2.2)paracyclophane.

Hexahydro[2.2]paracyclophane (6) and related compounds were prepared from the extrusion of sulfur dioxide from 2,11-dithia-4,5,6,7,8,9-hexahydro[3.3]paracyclophane 2,2,11,11-tetraoxide (9) by either the Ramberg−Backlund reaction or a flash pyrolysis. Compound 6 is the first cyclophane to contain both a benzene ring and a cyclohexane ring. Birch reduction of compound 6 gave a diene containing two double bonds in the same ring, which is different from the dienes obtained from the catalytic hydrogenation of [2.2]paracyclophane.

Kinetics and Mechanisms of N-Nitrosodimethylamine Formation upon Ozonation of N,N-Dimethylsulfamide-Containing Waters: Bromide Catalysis

N,N-Dimethylsulfamide (DMS), a newly identified, ubiquitous degradation product of the fungicide tolylfluanide, has been shown to be a N-nitrosodimethylamine (NDMA) precursor during ozonation. In this study, batch ozonation experiments in ultrapure buffered water, surface water, and tap water were performed to determine the kinetics and elucidate the mechanism of NDMA formation from DMS. It was found that at circumneutral pH, DMS reacts slowly with ozone (k approximately 20 M(-1) s(-1)) and moderately with hydroxyl radicals (k=1.5x10(9) M(-1)s(-1)). The reaction of DMS with these oxidants does not lead to NDMA. NDMA was only formed if bromide was present during ozonation of DMS-containing waters. Bromide is oxidized to hypobromous acid (HOBr) by ozone which then reacts with the primary amine of DMS to form a Br-DMS species. The rate limiting step of the formation of Br-DMS is the formation of HOBr. The reaction to form Br-DMS has an apparent second order rate constant at pH 8 of >3x10(4) M(-1)s(-1). The Br-DMS is transformed by ozone to NDMA and nitrate (k>or=5000 M(-1) s(-1)), with yields of 54% and 39%, respectively, based on the primary amine nitrogen of DMS. These reactions release bromide, making bromide a catalyst. NDMA is also formed during ozonation of DMS in the presence of hypochlorous acid (20-30% yield). The last step of NDMA formation is an intramolecular rearrangement with sulfur dioxide extrusion. On the basis of the mechanistic and kinetic information, it was possible to model NDMA formation in DMS-containing Lake Zurich water.

Atropisomerism of the 1,3-cyclohexadiene Derivatives Induced by Steric Congestion

3,4-Di-tert-butyl-2,5-dimethylthiophene 1-oxide (2) reacted with maleic anhydride to give the Diels–Alder adduct quantitatively. Oxidation of the sulfinyl group of the adduct and the thermal extrusion of sulfur dioxide from the resulting sulfone furnished 4,5-di-tert-butyl-3,6-dimethyl-3,5-cyclohexadiene-1,2-dicarboxylic acid anhydride (8) quantitatively. 8 showed atropisomerism that originates from the inhibited ring inversion of the cyclohexadiene ring by steric congestion. Mixtures of atropisomers were also obtained from the adducts of 2 and 1,4-benzoquinones.

Generation of Arylcyclopenta-1,3-dienes from Cyclopenteno-spiro-benzosultams: Synthesis of 2-Arylnorbornenes

Aza-ortho-xylylenes generated by thermal extrusion of sulfur dioxide from cyclopenteno-spiro-benzisothiazoline 2,2-dioxides undergo [1,5]-sigmatropic hydrogen shift leading to unstable arylcyclopentadienes that can be trapped with dienophiles to form arylnorbornenes.

SO2-Extrusion Reactions of Sulfonylated Nucleosides: A Novel Strategy for the Synthesis of Exocyclic Olefinic Thymidines

Analogues of 3′-C-methylidene-2′,3′-dideoxy-5-meth­yluridine have been synthesized from the 3′-deoxy-3′-sulfonylated derivatives of thymidine using sulfur dioxide extrusion reaction.

Synthesis of 5‐Hydroxy‐2‐(naphth‐2‐yl)chromone derivatives

Abstractmagnified imageThe Diels‐Alder reaction of 5‐hydroxy‐2‐styrylchromones with ortho‐benzoquinodimethane, generated “in situ” by thermal extrusion of sulfur dioxide from 1,3‐dihydrobenzo[c]thiophene 2,2‐dioxide, leads to 2‐(3‐aryl‐1,2,3,4‐tetrahydronaphth‐2‐yl)‐5‐hydroxychromones. These cycloadducts were dehydrogenated with DDQ, using classical thermal reflux conditions and microwave irradiation, affording the corresponding 2‐(3‐arylnaphth‐2‐yl)‐5‐hydroxychromones in high yields (48‐96%).

Chemistry of Diazafulvenium Methides in the Synthesis of Functionalized Pyrazoles

The chemistry of diazafulvenium methides generated by the thermal extrusion of sulfur dioxide from 2,2-dioxo-1H,3H-pyrazolo[1,5-c] [1,3]thiazoles is described. The diazafulvenium methides unsubstituted at C-7 participate in [8 pi + 2 pi] cycloadditions giving pyrazolo-annulated heterocycles resulting from the addition across the 1,7-position. 1-Methyl-diazafulvenium methides and 7,7-dimethyl-diazafulvenium methides undergo intramolecular sigmatropic [1,8]H shifts giving vinyl-1H-pyrazoles.

Synthesis of Substituted 1,3‐Diene Synthetic Equivalents by a Ru‐Catalyzed Diyne Hydrative Cyclization

Catalyzed by [CpRu(CH3CN)3]PF6, the hydrative cyclization of dipropargylic sulfone substrates provides an effective way to synthesize highly functionalized substituted 3-sulfolenes. The amount of water is crucial for the reactivity of this cycloisomerization reaction. The scope and limitations of the Ru-catalyzed cycloisomerization are discussed. A marked ketone-directing effect was observed for the first time in ruthenium-catalyzed cyclizations. A plausible mechanism for the ketone-directed cycloisomerization is also rationalized. The utility of this method was demonstrated by both sulfur dioxide extrusion of the 3-sulfolenes to afford 1,3-dienes and subsequent inter- or intramolecular Diels-Alder reactions.

Heterocycloaddition of thermally generated 1,2-diaza-1,3-butadienes to [60]fullerene

Stable C 60-fused tetrahydropyridazine derivatives were synthesized through the hetero-Diels–Alder cycloaddition of C 60 with 1,2-diaza-1,3-butadienes, which were generated in situ by the thermal extrusion of sulfur dioxide from 2,5-dihydro-1,2,3-thiadiazole-1,1-dioxides.

Brominative Indolization of an Unsaturated Bridgehead Sultam with Extrusion of Sulfur Dioxide

The dissolution of an unsaturated bridgehead sultam in liquid bromine at room temperature results in the formation of a pentabromo indole derivative in an unusual desulfonylative process.

N‐Vinyl‐ and C‐Vinylpyrroles from Azafulvenium Methides. Flash Vacuum Pyrolysis Route to 5‐Oxo‐5H‐pyrrolizines and 1‐Azabenzo[f]azulenes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Generation of ortho‐Quinone Methides upon Thermal Extrusion of Sulfur Dioxide from Benzosultones.

AbstractFor Abstract see ChemInform Abstract in Full Text.

N-Vinyl- and C-Vinylpyrroles from Azafulvenium Methides. Flash Vacuum Pyrolysis Route to 5-Oxo-5H-pyrrolizines and 1-Azabenzo[f]azulenes

1-Azafulvenium methides, generated from pyrrolo[1,2-c]thiazole-2,2-dioxides' thermal extrusion of sulfur dioxide, led to the synthesis of functionalized pyrroles. The intramolecular trapping of these transient 8pi 1,7-dipoles in pericyclic reactions, namely sigmatropic [1,8]H shifts and 1,7-electrocyclization, allowed the synthesis of N-vinylpyrroles and C-vinylpyrroles which, under flash vacuum pyrolysis conditions, are converted into 5-oxo-5H-pyrrolizines or 4-oxo-1,4-dihydro-1-aza-benzo[f]azulenes, respectively. These heterocycles can also be obtained directly from FVP of pyrrolo[1,2-c]thiazole 2,2-dioxides. The synthesis and X-ray structure of a new 6-oxocyclopenta[b]pyrrole derivative is also reported.

Generation of ortho-quinone methides upon thermal extrusion of sulfur dioxide from benzosultones

3 H-1,2-Benzoxathiole 2,2-dioxides (benzosultones) undergo thermal extrusion of sulfur dioxide to form ortho-quinone methides that enter Diels–Alder reaction with maleimides to form chroman 2,3-dicarboxylic acid derivatives.