Magnesium Halide‐promoted Ring‐opening Reaction of Cyclic Ether in the Presence of Phosphine Halide

A new route to the direct preparation of H‐phosphinate esters has been explored. The ring‐opening reaction of cyclic ether (tetrahydrofuran or tetrahydropyrane) was carried out with magnesium halide in the presence of phosphine halide (PRCl₂ or PCl₃). The process is straightforward and all the reagents are relatively cheap and readily available. Magnesium halide‐mediated THF ring‐opening (S_N2@C) and the subsequent S_N2@P elementary reactions that giving rise to the intermediate of haloalkyl phosphinates have been discussed based on our experimental findings ( Path I : S_N2@C−+S_N2@P). Another possible route, the direct S_N2 between THF (nucleophile) and phosphine halide (electrophile) that followed by THF ring opening by halide dissociated from phosphine halide ( Path II: S_N2@P−+S_N2@C), was also proposed. However, path II is the least likely reaction path because neutral THF is not a good nucleophile. H‐phosphinate esters could be readily available in the subsequent hydrolysis process. Considering the ionic bond strength in magnesium halides and the nucleophilicity of halides dissociated from MgX₂ in protic solvents like water, MgBr₂ is recommended for ring‐opening reactions of cyclic ethers.     

Kinetics of reactions of derivatives of bischloromethylphosphinic acid with amines

Conclusions The authors have made a kinetic study of nucleophilic replacement of chlorine by an amino group in derivatives of bischloromethylphosphinic acid. The process takes place by an S_N1-mechanism in the case of weak nucleophilic reagents (the aniline type) and by an S_n2-mechanism in the case of strong nucleophilic reagents (benzylamine type).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 175–177, January, 1969.     

Nucleophilic substitution inO-phenyldibenzofuranium and 10-phenylxanthonium cations

Reactions ofO-phenyldibenzofuranium tetrafluoroborate with nucleophiles (OH^?, NO₂ ^?, AcO^?) in aqueous media follow the S_NAr-mechanism and involve dehydroarenes. In DMSO, this salt smoothly reacts with NO₂ ^? and I^? with predominant opening of the furan ring. 10-Phenylxanthonium tetrafluoroborate readily arylates the NO₂ ^? ion in water (at the N and O atoms), mainly with predominant opening of the central ring, and is completely decomposed even with weak bases (NH₂OH, 2,4-dinitrophenylhydrazine). The Bayer—Villiger oxidation of this salt affords xanthone and 2-phenoxybenzoic acid.     

Ring opening in the amination of 3-X-1,2,4-triazines [1,2]. A 15N study

Evidence, based on ¹⁵N-labelling studies, has been obtained that the amino-dechlorination of 3-chloro-1,2,4-benzotriazine by potassium amide in liquid ammonia occurs according to an S_N(AE)^ipso process, while the amino-dechlorination of 3-chlorophenanthro[9,10-e]-1,2,4-triazine reacts for more than 90% according to a process involving a ring opening reaction [S_N(ANRORC)^ipos substitution].     

Organoaluminium assisted rearrangements of five-membered ring enol ethers with vinyl substituents

Such organoaluminium reagents as ⁱBu₃A1, PhC=CA1Et₂, and Et₂A1SPh mediate the title reactions in three different directions. (1) [3,3]sigmatropic rearrangement producing 7-membered rings. (2) isomerization to form vinylcyclopropane derivatives and (3) S_N2 type reaction with phenylthio anion via oxolane ring opening.     

SN(ANRORC) mechanism XX. Degenerate ring transformations in reactions of 1,2,4,5-tetrazines with hydrazine

Evidence is presented that the hydrazinolysis of 3-amino- (5) and 3-bromo-6-methyl-1,2,4,5-tetrazine ( 7 ) into the 3-hydrazino-6-methyl-1,2,4,5-tetrazine ( 6* ) with ¹⁵N-labelled hydrazine leads to incorporation of ¹⁵N in the 1,2,4,5-tetrazine ring. Thus in the hydrazino-deamination and hydrazino-debromination a S_N(ANRORC) mechanism is operative. Based on quantitative mass spectrometry it was found that 20-25% of both 5 and 7 reacts according to this S_N-(ANRORC) mechanism. The mechanism of these degenerate ring transformations is discussed.     

Lewis acid mediated nucleophilic ring opening followed by cycloaddition of 2-aryl-N-tosylaziridines with carbonyl compounds: further support towards an SN2-type mechanism

A highly regioselective S_N2-type ring opening of 2-aryl-N-tosylaziridines with carbonyl compounds in the presence of a Lewis acid to afford various 1,3-oxazolidines and 1,2-amino alcohols in excellent yields and moderate to high enantioselectivity is described. The formation of non-racemic products provides convincing evidence for the S_N2-type ring opening mechanism.     

The Reaction of Cyclopropyl Ketones with Acetyl Methanesulfonate. An efficient ring opening under neutral conditions with regiospecific enol acetate formation and stereo-controlled nucleophilic addition. Preliminary communication

Cyclopropyl ketones are readily cleaved under neutral conditions at room temperature by the combined action of acetyl methanesulfonate and nucleophiles such as Br^?, I^?, and MsO^?. The high-yield reaction involves regiospecific enol acetate formation with a stereoselectivity of nucleophile addition which is compatible with an S_N2-type opening of the cyclopropyl ring.     

Coordination compounds of disulphur dinitride

Summary Coordination compounds of the S₂N₂ molecule including methods for their preparation, reactivities, i.r. data, structures, and aspects of chemical bonding are reviewed. Methods of synthesis include reactions of S₂N₂, S₄N₄ or (NSCl)₃ with metal halides, metal complexes such as carbonyls, or even metals themselves. In all cases, the planar S₂N₂ ring is coordinated, usuallyvia both, of its nitrogen atoms so that S₂N₂ acts as a bridging ligand between two metal centres; short contact distances imply that halogen atoms linked to the metal atoms show some interaction with the sulphur atoms. The stability of S₂N₂ is greatly enhanced by coordination. In the i.r. spectra, two characteristic S₂N₂ vibrations assist identification of the S₂N₂ species, a ring stretching mode being observable atca. 850 cm^–1 and the out-of-plane deformation at 450–490 cm^–1.     

Lewis acid mediated SN2-type nucleophilic ring opening followed by [4+2] cycloaddition of N-tosylazetidines with aldehydes and ketones: synthesis of chiral 1,3-oxazinanes and 1,3-amino alcohols

A highly efficient strategy for Cu(OTf)₂ mediated S_N2-type nucleophilic ring opening followed by [4+2] cycloaddition reactions of enantiopure 2-phenyl-N-tosylazetidines with various aldehydes and ketones afforded a variety of substituted 1,3-oxazinanes and 1,3-amino alcohols in excellent yields, excellent de and good to excellent ee. The proposed S_N2-type mechanism of the cycloaddition reaction is supported by experimental evidence.     

Metal‐to‐Ligand Alkyl Migration Inducing Carbon–Sulfur Bond Cleavage in Dialkyl Yttrium Complexes Supported by Thiazole‐Containing Amidopyridinate Ligands: Synthesis,Characterization, and Catalytic Activity in the Intramolecular Hydroamination Reaction

Neutral Y^III dialkyl complexes supported by tridentate N^?,N,N monoanionic methylthiazole– or benzothiazole–amidopyridinate ligands have been prepared and completely characterized. Studies on their stability in solution revealed progressive rearrangement of the coordination sphere in the benzothiazole‐containing system through an unprecedented metal‐to‐ligand alkyl migration and subsequent thiazole ring opening. Attempts to synthesize hydrido species from the dialkyl precursor led to the generation of a dimeric yttrium species stabilized by a trianionic N^?,N,N^?,S^? ligand as the result of metal‐to‐ligand hydride migration with chemoselective thiazole ring opening and subsequent dimerization through intermolecular addition of the residual Y?H group to the imino fragment of a second equivalent of the ring‐opened intermediate. DFT calculations were used to elucidate the thermodynamics and kinetics of the process, in support of the experimental evidence. Finally, all isolated yttrium complexes, especially their cationic forms prepared by activation with the Lewis acid Ph₃C⁺[B(C₆F₅)₄]^?, were found to be good candidate catalysts for intramolecular hydroamination/cyclization reactions. Their catalytic performance with a number of primary and secondary amino alkenes was assessed.     

Dediazoniations of Arene Diazonium Ions in Homogeneous Solution. Part III: Heterolytic arylations in 2,2,2-trifluoroethanol - an SN1-or an SN2-reaction?

Benzenediazonium tetrafluoroborate in 2,2,2-trifluoroethanol decomposes to give fluorobenzene and phenyl 2,2,2-trifluoroethyl ether. In the presence of benzene, toluene, trifluoromethyl-benzene or anisole, the respective biphenyl derivatives are formed in addition to fluorobenzene and the ether. The distribution of the isomeric substituted biphenyls is consistent with an electrophilic substitution. No homolytic products (diazo tars, benzene) are formed. The reaction kinetics clearly show that ether formation and aryl-dediazoniations are of second-order type, i.e. that trifluoroethanol and the benzene derivatives mentioned above are rate-determining factors. It is shown that these results exclude the S_N1-mechanism which is usually assumed for heterolytic dediazoniations; free aryl cations are therefore not involved in these reactions. An S_N2-like mechanism seems to be the most likely, but one involving an encounter complex containing the dissociated benzenediazonium ion is also consistent with the experimental data.     

Acid-catalysed hydrolysis of N-sulphonyl sulphilimines—II

The basicity and the acid-catalysed hydrolysis of ph(R)SNTs and o-HC₆H₄(Me)SNTs sulphilimines have been studied by UV spectrophotometric and kinetic methods, respectively, in aqueous HClO₄ (1–10 M) and 1:1 (v/v) EtOH/H₂O-HClO₄ (0.5–6 M). Depending on the constitution of the substrates, sulphilimine hydrolysis can follow three different courses, according to rate-acidity profiles, Bunnett-Olsen's treatment, activation parameters and product analysis. Most typical for sulphilimines is S_N2 hydrolysis with S^IV-N bond cleavage. In this case the reaction starts with the nucleophilic addition of water and is promoted by acid-base catalysis. If a relatively stable carbenium ion can be formed from R group, an S_N1 reaction with S^IVC bond cleavage takes place. Sulphilimine with X = o-CO₂H due to neighbouring-group participation hydrolyses very rapidly via acyloxy-sulphurane and acyloxy-sulphonium ion intermediates with five-memembered ring (S_Ni reaction involving S^IVN bond cleavage).     

ELECTRON-RICH THIAZENES: SOME PRINCIPLES OF SYNTHESIS AND STRUCTURE

Abstract

General methods of preparation and typical bond distances and bond angles (at sulfur and nitrogen) are reviewed for cyclic sulfur–nitrogen compounds. Correlations between sulfur-nitrogen bond distance and unstrained bond angles in SNS and NSN groups can be used to assess angular strain in 4 and 5 atom thiazene rings and the optimum ring geometries of larger thiazene cations such as S₅N⁺ ₅ and S₄N_{2+ 4}. The geometry of S₃N^? ₃ is also discussed.     

A new synthetic route to cyclophosphadithiatriazenes: synthesis and X‐ray structural characterization of the first spirocycle containing thiadiazaphosphetidine and phosphadithiatriazene heterocycles

The phosphetidine 2,4‐Di‐tert‐butyl‐3‐chloro‐1λ⁶‐thia‐2,4‐diaza‐3‐phosphetidine‐1,1‐dioxide, O₂S (^tBuN)₂PCl, reacts with tetrasulfur tetranitride, S₄N₄, in benzene under reflux to afford the novel 4,6‐spirocycle in moderate yield. The deep‐blue crystals of the spirocycle are airstable and high melting in nature. The spiro phosphorus atom subtends a four‐membered P^VS^VIN₂ ring which is saturated, and a six‐membered P^VS N₃ ring which is unsaturated. The single‐crystal X‐ray structure of this first example of the spirocycle reveals a planar PSN₂ ring and a puckered PS₂N₃ ring and the molecule is symmetric in nature. Copyright © 2006 John Wiley & Sons, Ltd.     

A Synthetic Route to Chiral Dihydrobenzothiazines through Ring Opening of Activated Aziridines with 2‐Halothiophenols/Copper‐Powder‐Mediated C−N Cyclization

A simple protocol for the synthesis of dihydrobenzothiazines through regio‐ and stereoselective S_N2‐type ring opening of N‐tosylaziridines with sulfur nucleophiles followed by copper‐powder‐mediated intramolecular C?N cyclization in excellent yields (up to 95 %) with high diastereo‐ and enantioselectivity (up to >99 %) is reported.     

Cyclothiazenokomplexe von Molybdän(V) und (VI), sowie von Wolfram(VI) Die Kristallstruktur von (PPh4)2[MoCl3(N3S2)]2 · 2 CH2Cl2

Cyclothiazeno Complexes of Molybdenum(V), Molybdenum(VI), and Tungsten(VI). Crystal Structure of (PPh₄)₂[MoCl₃(N₃S₂)]₂ · 2 CH₂Cl₂ . From excess trithiazylchloride and molybdenum or tungsten hexacarbonyl, respectively, the cyclothiazeno complexes [MCl₃(N₃S₂)]₂(S₂N₂) are obtained. They possess metal atoms linked via a planar S₂N₂ ring. The corresponding bromo compounds [MBr₃(N₃S₂)]₂(S₂N₂) can be obtained in liquid bromine from S₄N₄ and MoBr₄ or WBr₆, respectively, or from S₄N₄ with the corresponding metal hexacarbonyls in the presence of bromine. Thermolysis of [WBr₃(N₃S₂)]₂(S₂N₂) yields [WBr₃(N₃S₂)]₂ which is dimerized via nitrogen bridges. When [MoCl₃(N₃S₂)]₂(S₂N₂) reacts with tetraphenylphosphonium chloride in dichloromethane, the S₂N₂ acts as reducing agent, and the paramagnetic molybdenum(V) complex (PPh₄)₂[MoCl₃(N₃S₂)]₂ · 2 CH₂Cl₂ is obtained (μ_eff = 1.2 B.M.). The i.r. spectra are reported. The crystal structure of (PPh₄)₂[MoCl₃(N₃S₂)]₂ · 2 CH₂Cl₂ was determined by X-ray diffraction (2524 independent reflexions, R = 0.052). It crystallizes in the space group P1 with the lattice con- stants a = 943.9, b = 1209.6, c = 1469.2 pm, α = 69.27, β = 72.20 and γ = 82.08°, Z = 1. There are tetraphenylphosphonium cations and centrosymmetric, dimeric anions [MoCl₃(N₃S₂)]₂^2?. The molybdenum atoms are part of six-membered cyclothiazeno rings MoN₃S₂ with MoN bond lengths of 177 and 197 pm; the N atom with the longer MoN bond is linked to the second Mo atom, so that a planar Mo₂N₂ ring results; this ring is nearly coplanar with the two MoN₃S₂ rings. Furthermore, each molybdenum atom is linked with three chlorine atoms with MoCl bond lengths of 240–242 pm, so that the Mo atoms possms a distorted octahedral coordination.     

Die Reaktionen von Eisen(III)-chlorid mit Trithiazylchlorid. Die Kristallstruktur von [S4N4Cl]+[FeCl4]⊖

Reactions of Iron Trichloride with Trithyazyl Chloride. Crystal Structure of [S₄N₄Cl]⁺[FeCl₄]^? Iron trichloride reacts with (NSCl)₃ yielding S₄N₄[FeCl₄]₂, S₃N₃Cl₂[FeCl₄] or S₄N₄Cl[FeCl₄], depending on the reaction conditions. The i.r. spectra prove the presence of [FeCl₄]^? ions for all three compounds. The ⁵⁷Fe-Mössbauer spectra show a slight quadrupole splitting at 80 K for S₃N₃Cl₂[FeCl₄] (ΔE^Q = 0.42 mm · s^?1) and S₄N₄Cl[FeCl₄] (ΔE^Q = 0.23 mm · s^?1), which indicates a slight deformation of the FeCl₄^? tetrahedra. The crystal structure of S₄N₄Cl[FeCl₄] was determined and refined with X-ray diffraction data (2549 independent reflexions, R = 0.026). S₄N₄Cl[FeCl₄] crystallizes in the triclinic space group P1 with two formula units per unit cell. The lattice constants are a = 712, b = 911, c = 1006 pm, α = 76.5°, β = 83.8° and γ = 80.5°. The structure consists of the so far unknown [S₄N₄Cl]^⊕ cations and slightly deformed FeCl₄^? ions. The [S₄N₄Cl]^⊕ ion consists of a S₄N₄ ring built up of two nearly planar S₃N₂ fragments having a dihedral angle of 136°. The average SN bond length is 157 pm, the SCI bond length 214 pm.     

Nucleophilic Reactivity of Ethers Against Terminal Epoxides in the Presence of BF3: A Mechanistic Study

In the presence of BF₃, a series of symmetrical and unsymmetrical ethers reacted with epichlorohydrin and 2‐[(benzyloxy)methyl]oxirane, two terminal epoxides, to afford 1‐alkoxy‐3‐chloropropan‐2‐ol and 1‐alkoxy‐3‐(benzyloxy)propan‐2‐ol. The cleavage of unsymmetrical ethers occurred via an S_N2 or S_N1 mechanism. Secondary epoxides did not give similar ring‐opening products.     

Die Reaktion von Trithiazylchlorid mit Titantetrachlorid Die Kristallstruktur von (S4N5)2[Ti2Cl10]

Reaction of Trithiazyl Chloride with Titanium Tetrachloride. Crystal Structure of (S₄N₅)₂[Ti₂Cl₁₀] In the reaction of trithiazyl chloride with titanium tetrachloride, chlorine is abstracted and the brown-yellow adduct TiCl₄(N₂S₂) is obtained. In this compound — according to its i.r. spectrum — a N₂S₂ ring is bonded to the titanium via the N atoms, thus forming a polymer. As a by-product, brown crystalline (S₄N₅)₂[Ti₂Cl₁₀] forms. Its crystal structure was determined and refined with X-ray diffraction data (R = 0.042 for 812 reflexions). It crystallizes in the monoclinic space group P2₁/c with two formula units per unit cell. The lattice constants are a = 670, b = 1 633, c = 1108 pm, β = 97.24°. The structure consists of S₄N₅^⊕ cations, which are nearly equal to those in [S₄N₅]Cl, and [Ti₂Cl₁₀]^2? anions, which are nearly identical with those in (PCl₄)₂[Ti₂Cl₁₀].