Bimolecular Homolytic Substitutions at Nitrogen: An Experimental and Theoretical Study on the Gas‐Phase Reactions of Alkyl Radicals with NF3

The X‐ray irradiation of binary mixtures of alkyl iodides R?I (R=CH₃, C₂H₅, or i‐C₃H₇ radicals) and NF₃ produces R?NF₂ and R?F. Based on calculations performed at the CCSD(T), MRCI(SD+Q), G3B3, and G3 levels of theory, the former product arises from a bimolecular homolytic substitution reaction (S_H2) by the alkyl radicals R, which attack the N atom of NF₃. This mechanism is consistent with the suppression of R?NF₂ by addition of O₂ (an efficient alkyl radical scavenger) to the reaction mixture. The R?F product arises from the attack of R to the F atom of NF₃, but additional contributing channels are conceivably involved. The F‐atom abstraction is, indeed, considerably more exothermic than the S_H2 reaction, but the involved energy barriers are comparable, and the two processes are comparably fast.     

(o-Phenylenediamino)borylstannanes: Efficient Reagents for Borylation of Various Alkyl Radical Precursors

(o-Phenylenediamino)borylstannanes were newly synthesized to achieve radical boryl substitutions of a variety of alkyl radical precursors. Dehalogenative, deaminative, decharcogenative, and decarboxylative borylations proceeded in the presence of a radical initiator to give the corresponding organic boron compounds. Radical clock experiments and computational studies have provided insights into the mechanism of the homolytic substitution (S_H2) of the borylstannanes with alkyl radical intermediates. DFT calculation disclosed that the phenylenediamino structure lowered the LUMO level including the vacant p-orbital on the boron atom to enhance the reactivity to alkyl radicals in S_H2. Moreover, C(sp³)-H borylation of THF was accomplished using the triplet state of xanthone.     

A study of radicals arising in the low-temperature radiolysis of thiophene and some of its derivatives

EPR was used to investigate the radicals formed by radiolysis of furan, thiophene, and some of their substitution products having the general formula C₄H₃RS, where R = Cl, Br, COOH, C(CH₃)₃, and of di-tert-butylthiophene. By analyzing the EPR spectra it is shown that radicals formed by radiolysis of furan, thiophene, their alkyl substitution products, and 2-thiophene carboxylic acid arise in primary radiation-chemical events with splitting of the C-H bond in both ring and side chain. Characteristic of the radiolysis of these compounds is formation of secondary radicals by addition of hydrogen atoms at the double bond of the heteroaromatic ring. The values of the hyperfine splittings in the spectra of the secondary radicals are, for protons of methylene group 32 e [positions 2(5)] or 40 e [positions 3(4)], and 13 e for protons of the thiophene ring. In radiolysis of 2-chlorothiophene and 3-bromothiophene the main products are radicals with the unpaired electron localized on the sulfur atom.     

Synthesis and properties of new macrocyclic compounds: Utilization of bond character of hypervalent sulfur in tetraazathiapentalene derivatives

2,3‐Bis[(p‐isothiocyanatomethylphenyl)methyl]‐6,7‐dihydro‐5H‐2a‐thia(2a‐S_IV)‐2,3,4a,7a‐tetraaza‐cyclopent[cd]indene‐1,4(2H,3H)‐dithione ( 3 ), prepared by the reaction of 2,3‐dimethyl‐6,7‐dihydro‐5H‐2a‐thia(2a‐S^IV)‐2,3,4a,7a‐tetraazacyclopent‐[cd]indene‐1,4(2H,3H)‐dithione ( 1 ) with p‐xylylene diisothio‐cyanate, reacted with N,N′‐dialkyl substituted diamines to give macrocyclic compounds bearing hypervalent sulfur by a ring closure reaction in good yields. These macrocyclic compounds were converted into ring‐expanded macrocyclic compounds with release of the hypervalent sulfur by treating with NaBH₄ and CF₃COOH.     

Effects of polysulfides on the polymerization of methyl methacrylate

The effect of organic sulfur compounds on the radical polymerization of methyl methacrylate initiated by azobisisobutyronitrile at 50°C. has been studied. The sulfur compounds used were benzene-type polysulfides (C₆H₅CH₂? S_n? CH₂C₆H₅; n = 0–4), benzyl mercaptan, and sulfur (S₈). All sulfur compounds studied, except dibenzyl, dibenzyl monosulfide, and dibenzyl disulfide, were found to behave as retarders under these experimental conditions. Chain-transfer constants of these compounds were determined from rate measurements and from the conventional method based on numberaverage degree of polymerization. Chain-transfer constants of benzyl-type polysulfides were less than those of mercaptan and sulfur and increased with increasing sulfur. The correlation of the reactivities of sulfur compounds as transfer agents and their molecular structures is discussed.     

Novel pseudopolymorph of the active metabolite of perindopril

The dimethyl sulfoxide hemisolvate of perindoprilat [systematic name: (1S)‐2‐((S)‐{1‐[(2S,3aS,7aS)‐2‐carboxyoctahydro‐1H‐indol‐1‐yl]‐1‐oxopropan‐2‐yl}azaniumyl)pentanoate dimethyl sulfoxide hemisolvate], C₁₇H₂₈N₂O₅·0.5C₂H₆OS, an active metabolite of perindopril, has been synthesized, structurally characterized by single‐crystal X‐ray diffraction and compared with its ethanol disolvate analogue [Pascard et al. (1991). J. Med. Chem. 34 , 663–669]. Both compounds crystallize in the orthorhombic P2₁2₁2₁ space group in the same zwitterionic form, with a protonated alanine N atom and an anionic carboxylate group at the n‐alkyl chain. The three structural units present in the unit cell (two zwitterions and the solvent molecule) are held together by a rich system of O—H...O, N—H...O and C—H...O hydrogen‐bond contacts.     

(Benzoxazole‐2‐thiol­ato‐S)(benzoxazole‐2‐thione‐S)­bis­(tri­phenylphosphine)copper(I)

The Cu atom in [Cu(C₇H₄NOS)(C₇H₅NOS)(C₁₈H₁₅P)₂] is tetrahedrally coordinated by a P₂S₂ donor set. One S atom is derived from neutral benzoxazole‐2‐thione and the other from the deprotonated form of the ligand. The two sulfur ligands are connected via an N—H?N interaction, leading to the formation of an eight‐membered ring.     

Microwave‐assisted synthesis of 1,3′‐diaza‐flavanone/flavone and their alkyl derivatives with antimicrobial activity

A simple environmentally friendly solid‐phase microwave‐assisted method was used to synthesis of the 1,3′‐diazaflavanone ( 2 ) and 1,3′‐diazaflavone ( 3 ) from the cyclization of 2′‐amino (E)‐3″‐azachalcone ( 1 ). Ten new N‐alkyl (C_5–12,14,15)‐substituted 1,3′‐diazaflavanonium bromides ( 2a–j ) were prepared from compound 2 with corresponding alkyl halides in acetonitrile under reflux. In addition, nine new N,N′‐dialkyl (C_5–12,14)‐substituted 1,3′‐diazaflavonium bromides ( 3a–i ) were also synthesized from compound 3 with corresponding alkyl halides using basic silica in acetonitrile. The antimicrobial activities of compounds 1–3 , 2a–j , and 3a–i were tested against Gram‐positive (G+) (Bacillus subtilis, Staphylococcus epidermidis, Staphylococcus aureus, and Enterococcus faecalis) and Gram‐negative (G?) (Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa, Proteus vulgaris, Salmonella typhimirium, Yersinia pseudotuberculosis, and Enterobacter cloaceae) microorganisms. They showed good antimicrobial activity against the Gram‐positive bacteria tested with the minimal inhibitory concentration values less than 7.8 μg/mL in most cases. The optimum length of the alkyl chain for better and broader activity is situated in the range of 9–12 carbon atoms in the series of compounds 2a–j and five to six carbon atoms in the series of compounds 3a–i . The nonalkylated compounds 1–3 were not effective, as were the ones alkylated with five or six C alkyl groups ( 2a and 2b ) and 8–13 C alkyl groups for N,N′‐dialkyl compounds ( 3c–3i ). The antimicrobial activity increased as the length of the alkyl substitution increased from 8 to 12 carbons in compounds 2a–j . However, antimicrobial activity decreased as the length of the alkyl substitution increased from 7 to 13 carbons in compounds 3c–i . J. Heterocyclic Chem., (2012)     

A Stable Dimer of SiS2 Arranged between Two Carbene Molecules

The Me‐cAAC:‐stabilized dimer of silicon disulfide (SiS₂) has been isolated in the molecular form as (Me‐cAAC:)₂Si₂S₄ ( 2 ) at room temperature [Me‐cAAC:=cyclic alkyl(amino) carbene]. Compound 2 has been synthesized from the reaction of (Me‐cAAC:)₂Si₂ with elemental sulfur in a 1:4 molar ratio under oxidative addition. This is the smallest molecular unit of silicon disulfide characterized by X‐ray crystallography, electron ionization mass spectrometry, and NMR spectroscopy. Structures with three sulfur atoms arranged around a silicon atom are known; however, 2 is the first structurally characterized silicon–sulfur compound containing one terminal and two bridging sulfur atoms at each silicon atom. Compound 2 shows no decomposition after storing for three months in an inert atmosphere at ambient temperature. The bonding of 2 has been further studied by theoretical calculations.     

Reaction mechanism and modeling study for the oxidation by SO2 of o‐xylene and p‐xylene in Claus process

Claus process, comprising of a furnace and a catalytic unit, is used to produce sulfur from H₂S. The aromatic contaminants (benzene, toluene, and xylenes) in H₂S feed form soot, and clog and deactivate the catalysts. Xylenes are known to be the most damaging ones. Therefore, there is a need to oxidize them in the furnace to enhance catalyst life. This article presents a kinetics study on the oxidation of o‐ and p‐xylene radicals by SO₂ (an oxidant that is already present in the furnace) using density functional theory and a composite method. The mechanism begins with H‐abstraction from xylenes to form xylyl radicals, followed by exothermic addition of SO₂ to them. The breakage of O S bond in the xylyl‐SO₂ adducts leads to the loss of SO molecule, while the remaining O atom on them helps in their oxidation. The isomerization study shows that less‐stable dimethylphenyl radicals have a high tendency to isomerize to resonantly stabilized methylbenzyl radicals. However, methylbenzyl radicals have lower reactivity toward SO₂ than dimethylphenyl radicals. The reaction rate constants were found using transition state theory. The reactor simulations reveal that p‐xylene has lower reactivity toward SO₂ than o‐xylene, and CO, SO, and CHO are the main by‐products of oxidation.     

[1,2‐P2S8]2− – a New Member of the Thiophosphate Family: Synthesis,Crystal Structure and Vibrational Spectrum of [NH4(2.2.2‐cryptand)]2[1,2‐P2S8] and [NH4(18‐crown‐6)]2[1,2‐P2S8]·H2O

Colourless block‐shaped crystals of [(NH₄)₂(2.2.2‐cryptand)₂][P₂S₈] ( 1 ) and [(NH₄)₂(18‐crown‐6)₂][P₂S₈]·H₂O ( 2 ) could be obtained by the reaction of an aqueous solution of ammonium hexathiohypodiphosphate, (NH₄)₄P₂S₆·2 H₂O, with sulfur and 2.2.2‐cryptand or 18‐crown‐6. The crystal structures of both compounds have been determined by single‐crystal X‐Ray diffraction analysis. Compound 1 crystallizes in the monoclinic space group C2/c with a = 2032.7(2), b = 1243.6(2), c = 2244.6(2) pm, β = 98.64(1)°, and Z = 8, whereas compound 2 crystallizes also monoclinic in the space group P2₁/c with a = 2121.3(2), b = 865.5(1), c = 2345.4(2) pm, β = 91.96(1)°, and Z = 4. It could be established that the title compounds contain a new type of six‐membered [1,2‐P₂S₄] ring with P – P bond and three S – S linkages. The tetrahedral environment of each phosphorus is completed by a (formally) single and double bonded sulfur atom attached externally to the [1,2‐P₂S₄] ring. These terminal PS₂ units are mesomerically stabilized according to their P – S distances. FT‐IR and FT‐Raman spectra of the title compounds are recorded and interpreted.     

Preference for the Diels–Alder addition of dienes syn to the O atom in cross‐conjugated spiro­cyclic cyclo­hexadienones

In the Diels–Alder reaction, the preferred addition of dienes syn to the O atom in cross‐conjugated cyclo­hexadienones containing an oxa‐­spiro ring system is observed. The two structures reported here, namely rel‐(1R,4aR,9S,9aS,10R)‐4a,9,9a,10‐tetra­hydro‐9,10‐di­phenyl­spiro­[9,10‐epoxy­anthra­cene‐1(4H),2′‐oxiran]‐4‐one, C₂₇H₂₀O₃, and rel‐(1R,4aS,9R,9aS,10S)‐4a,9,9a,10‐tetra­hydro‐9,10‐di­phenyl­spiro­[9,10‐epoxy­anthracene‐1(4H),2′‐oxetane]‐4‐one, C₂₈H₂₂O₃, are the minor and sole products, respectively, of the reactions of di­phenyl­isobenzo­furan with two slightly different cyclo­hexadienones. These structures differ in the size of the oxa‐­spiro ring, by one C atom, and in the relative configuration at the spiro­cyclic ring C atom, leading to some minor conformational differences between the two compounds.     

Isomeric 3‐ and 4‐chloro‐N‐[1‐(1H‐pyrrol‐2‐yl)ethylidene]aniline

The title isomers, namely 3‐chloro‐N‐[1‐(1H‐pyrrol‐2‐yl)ethylidene]aniline, (I), and 4‐chloro‐N‐[1‐(1H‐pyrrol‐2‐yl)ethylidene]aniline, (II), both C₁₂H₁₁ClN₂, differ in the position of the chlorine substitution. Both compounds have the basic iminopyrrole structure, which shows a planar backbone with similar features. The dihedral angle formed by the planes of the pyrrole and benzene rings is 75.65 (7)° for (I) and 86.56 (8)° for (II). The H atom bound to the pyrrole N atom is positionally disordered and partial protonation occurs at the imino N atom in (I), while this phenomenon is absent from the structure of (II). Packing interactions for both compounds include intermolecular N—H...N hydrogen bonds and C—H...π interactions, forming centrosymmetric dimers for both (I) and (II).     

Structure,Stereochemistry and Dynamics of Tetranuclear Polyhydride Clusters Containing Chiral Heterobidentate Phosphanes

A novel chiral phosphane (S)‐2‐(4‐isopropyl‐2‐oxazoline‐2‐yl)phenyl‐di‐N‐pyrrolylphosphane (S‐PyrPOx) based on asymmetric oxazoline ring has been prepared and characterised. Reaction of this ligand and its phenyl‐substituted analogue (S‐PhPOx) with H₄Ru₄(CO)₁₂ and H₃RhOs₃(CO)₁₂ gave substituted derivatives H₄Ru₄(CO)₁₀(1,1‐PhPOx) ( 2 ), H₄Ru₄(CO)₁₀(1,1‐PyrPOx) ( 3 ), and H₃RhOs₃(CO)₁₀(1,1‐PyrPOx) ( 4 ), which were structurally characterised by X‐ray crystallography in solid state and by a variety of multinuclear NMR spectroscopic measurements in solution. In all studied clusters the coordinated ligands form five‐membered chelate rings through phosphorus and nitrogen atoms of oxazoline moiety to afford a novel chiral center associated with the substituted metal atom. The substitution reactions demonstrate extremely high stereoselectivity, which results in formation of only one diastereomer in all three cases to give S,S isomer in 2 and S,R isomer in 3 and 4 .     

Efficient Synthesis of 1‐Arylquinoxalin‐2(1H)‐ones via Cyclocondensation of N‐Aryl‐Substituted 2‐Nitrosoanilines with Functionalized Alkyl Acetates

N‐Aryl‐substituted 2‐nitrosoanilines (=2‐nitrosobenzenamines) 1 , readily available by nucleophilic substitution of the ortho‐H‐atom in nitroarenes with arenamines, react with 2‐substituted acetic acid esters in the presence of a weak base giving 1‐arylquinoxalin‐2(1H)‐ones (Scheme 2). This cyclocondensation allows for the synthesis of compounds 2 – 4 , unsubstituted at C(3) or substituted by alkyl, aryl, ester, amide, and keto groups, in good to excellent yields (Tables 1–4).     

Reactivity of 4‐thiothymidine with Fenton reagent investigated by UV‐visible spectroscopy and electrospray ionization mass spectrometry

The reactivity of the sulfur‐containing nucleoside 4‐thio‐(2′‐deoxy)‐thymidine usually abbreviated as 4‐thio‐thymidine, (S⁴‐TdR) under Fenton conditions, ie, in the presence of H₂O₂ and catalytic amounts of Fe(II), was investigated by UV‐vis spectroscopy and electrospray ionization single and tandem mass spectrometry (ESI‐MS and MS/MS). S⁴‐TdR hydroxylated on the S atom was found to be a key reaction intermediate, ultimately leading to (2′‐deoxy)‐thymidine usually abbreviated as thymidine, (TdR) as the main reaction product. This finding was in accordance with the outcome of the reaction between S⁴‐TdR and H₂O₂, previously investigated in our laboratory. On the other hand, the additional presence of ?OH radicals, induced by the Fe(II)/H₂O₂ combination, led to the increased generation of another interesting S⁴‐TdR product, already observed after its reaction with H₂O₂ alone, ie, the covalent dimer including a S? S bridge between two S⁴‐TdR molecules. More importantly, multihydroxylated derivatives of S⁴‐TdR and TdR were detected as peculiar products obtained under Fenton conditions. Among them, a product bearing an OH group both on the methyl group linked to the thymine ring and on the C5 atom of the ring was found to prevail. The results obtained during this study, integrated by those found previously in our laboratory, indicate 4‐thiothymidine as a promising molecular probe for the recognition, through a careful characterization of its reaction products, of the prevailing species among reactive oxygen species (ROS) corresponding to singlet‐state oxygen, hydrogen peroxide, and hydroxylic radical.     

Stereochemistry of two new polyfunctionalized gem‐dihalo­cyclo­propanes

The two new gem‐dihalogeno­cyclo­propanes (1′S,3R)‐3‐(2′,2′‐di­chloro‐1′‐methyl­cyclo­propyl)‐6‐oxoheptanoic acid, C₁₁H₁₆­Cl₂O₃, (2), and (1′S,3R)‐3‐(2′,2′‐di­bromo‐1′‐methyl­cyclo­propyl)‐6‐oxoheptanoic acid, C₁₁H₁₆Br₂O₃, (3), are isostructural. Both present two stereogenic centers at C1′ and C3. The absolute configuration was determined by X‐ray methods. The cyclo­propyl rings are unsymmetrical, the shortest bond being distal with respect to the alkyl‐substituted C atom.     

Syntheses and Characterization of Half—Sandwich Zirconium Complexes with Dichalcogenolate o—Carborane Ligands

Metallocene complex Cp2^ttZrCl2(Cp^tt=η^5-1,3-^tBu2C5H3)(1)has been prepared from the reaction of LiCp^tt with ZrCl4 in good yield.Reactions of 1 with dilithium dichalcogenolate o-carboranes afforded new type of half-sandwich compounds with dichalcogenolate o-carboranyl ligands,[Li(THF)4][Cp^ttZr(E2C2B10H10)2](E=S,2a;E=Se,2b)in which only one cyclopentadienyl ring ligand existed.Complexes 1 and 2a were structurally characterized by X-ray analyses.In complex 2a,the Zr(IV)ion is η^5-bound to one 1,3-ditert-cyclopentadienyl ring and σ-bound to four μ2-sulfur atoms of two dithio-carboranes.the zirconium atom and four sulfur atoms form a distorted pyramid.The coordination sphere around the zirconium atom resembles in a piano stool structure with four legs of sulfur stoms and the fulcrum at the zirconium stom.     

Crystallographic report: Di(p‐fluorobenzyl)tin bis(N,N‐dimethyldithiocarbamate)

The tin atom in (p–FC₆H₄CH₂)₂(S₂CNMe)₂ is in a skewed‐trapezoidal bipyramidal geometry defined by two sets of sulfur donors derived from the dithiocarbamate ligands and two carbon atoms from the tin‐bound p‐fluorobenzyl substituents; C? Sn? C is 129.2(2)°. Copyright © 2004 John Wiley & Sons, Ltd.     

A non‐oxo methanolate‐bridged divanadium(IV) complex with tris(2‐sulfanidylphenyl)phosphane ligands: synthesis,structural characterization and magnetic investigation

Vanadium chemistry is of interest due its biological relevance and medical applications. In particular, the interactions of high‐valent vanadium ions with sulfur‐containing biologically important molecules, such as cysteine and glutathione, might be related to the redox conversion of vanadium in ascidians, the function of amavadin (a vanadium‐containing anion) and the antidiabetic behaviour of vanadium compounds. A mechanistic understanding of these aspects is important. In an effort to investigate high‐valent vanadium–sulfur chemistry, we have synthesized and characterized the non‐oxo divanadium(IV) complex salt tetraphenylphosphonium tri‐μ‐<!?tlsb=‐0.11pt>methanolato‐κ⁶O:O‐bis({tris[2‐sulfanidyl‐3‐(trimethylsilyl)phenyl]phosphane‐κ⁴P,S,S′,S′′}vanadium(IV)) methanol disolvate, (C₂₄H₂₀P)[V^IV₂(μ‐OCH₃)₃(C₂₇H₃₆PS₃)₂]·2CH₃OH. Two V^IV metal centres are bridged by three methanolate ligands, giving a C2‐symmetric V₂(μ‐OMe)₃ core structure. Each V^IV centre adopts a monocapped trigonal antiprismatic geometry, with the P atom situated in the capping position and the three S atoms and three O atoms forming two triangular faces of the trigonal antiprism. The magnetic data indicate a paramagnetic nature of the salt, with an S = 1 spin state.