Diacenaphtho[1,2-c:1,2-e]-1,2-dithiin: synthesis, structure and reactivity

Diacenaphtho[1,2-c:1^′,2^′-e]-1,2-dithiin 2 was synthesized in 23% yield by the reaction of acenaphthylene with elemental sulfur at 120 °C. This reaction also afforded either diacenaphtho[1,2-b:1^′,2^′-d]thiophene 1 or diacenaphtho[1,2-b:1^′,2^′-e]-dihydro[e]-1,4-dithiin 3 depending on the reaction time. Compound 2 was desulfurized and converted to 1 under UV-vis irradiation in a benzene solution. Reaction of 2 with Pt(COD)₂ yielded the complex Pt(COD)(C₂₄H₁₂S₂) 4 (COD=1,5-cyclooctadiene) by insertion of a Pt(COD) group into the S-S bond of 2. When heated, 4 was desulfurized and converted to 1 by elimination of a (COD)PtS grouping. Compounds 1-4 were characterized crystallographically.     

Three-component 1,2-carboamination of vinyl boronic esters via amidyl radical induced 1,2-migration

Three-component 1,2-carboamination of vinyl boronic esters with alkyl/aryl lithium reagents and N-chloro-carbamates/carboxamides is presented. Vinylboron ate complexes generated in situ from the boronic ester and an organo lithium reagent are shown to react with readily available N-chloro-carbamates/carboxamides to give valuable 1,2-aminoboronic esters. These cascades proceed in the absence of any catalyst upon simple visible light irradiation. Amidyl radicals add to the vinylboron ate complexes followed by oxidation and 1,2-alkyl/aryl migration from boron to carbon to give the corresponding carboamination products. These practical cascades show high functional group tolerance and accordingly exhibit broad substrate scope. Gram-scale reaction and diverse follow-up transformations convincingly demonstrate the synthetic potential of this method.

Three-component 1,2-carboamination of vinyl boronic esters with alkyl/aryl lithium reagents and N-chloro-carbamates/carboxamides is presented.

Alkenes are important and versatile building blocks in organic synthesis. 1,2-Difunctionalization of alkenes offers a highly valuable synthetic strategy to access 1,2-difunctionalized alkanes by sequentially forming two vicinal σ-bonds.^1a–h Among these vicinal difunctionalizations, the 1,2-carboamination of alkenes, in which a C–N and a C–C bond are formed, provides an attractive route for the straightforward preparation of structurally diverse amine derivatives (Scheme 1a).^2a–c Along these lines, transition-metal-catalyzed or radical 1,2-carboaminations of activated and unactivated alkenes have been reported.^3a–p However, the 1,2-carboamination of vinylboron reagents, a privileged class of olefins,^4a–h to form valuable 1,2-aminoboron compounds which can be readily used in diverse downstream functionalizations,^{5a–c,6a–d} has been rarely investigated. To the best of our knowledge, there are only two reported examples, as shown in Schemes 1b and c. In 2013, Molander disclosed a Rh-catalyzed 1,2-aminoarylation of potassium vinyltrifluoroborate with benzhydroxamates via C–H activation (Scheme 1b).⁷ Thus, the 1,2-carboamination of vinylboron reagents is still underexplored but highly desirable.Open in a separate windowScheme 1Intermolecular 1,2-carboamination of alkenes.1,2-Alkyl/aryl migrations induced by β-addition to vinylboron ate complexes have been shown to be highly reliable for 1,2-difunctionalization of vinylboron reagents (Scheme 1c).^4d–h In 1967, Zweifel''s group developed 1,2-alkyl/aryl migrations of vinylboron ate complexes induced by an electrophilic halogenation.⁸ In 2016, the Morken group reported the electrophilic palladation-induced 1,2-alkyl/aryl migration of vinylboron ate complexes.^9a–k Shortly thereafter, we,^10a–c Aggarwal,^11a–c and Renaud¹² developed alkyl radical induced 1,2-alkyl/aryl migrations of vinylboron ate complexes. In these recent examples, the migration is induced by a C-based radical/electrophile, halogen and chalcogen electrophiles.^13a,bIn contrast, N-reagent-induced migration of vinylboron ate complexes proceeding via β-amination is not well investigated. To our knowledge, as the only example the Aggarwal laboratory described the reaction of a vinylboron ate complex with an aryldiazonium salt as the electrophile, but the desired β-aminated rearrangement product was formed in only 9% NMR yield (Scheme 1c).^13a No doubt, β-amino alkylboronic esters would be valuable intermediates in organic synthesis. Encouraged by our continuous work on amidyl radicals^14a–i and 1,2-migrations of boron ate complexes,^{10a–c,15a–f} we therefore decided to study the amidyl radical-induced carboamination of vinyl boronic esters for the preparation of 1,2-aminoboronic esters. N-chloroamides were chosen as N-radical precursors,^16a–c as these N-chloro compounds can be easily prepared from the corresponding N–H analogues.¹⁷ Herein, we present a catalyst-free three-component 1,2-carboamination of vinyl boronic esters with N-chloroamides and readily available alkyl/aryl lithium reagents (Scheme 1d).We commenced our study by exploring the reaction of the vinylboron ate complex 2a with tert-butyl chloro(methyl)carbamate 3a applying photoredox catalysis. Complex 2a was generated in situ by addition of n-butyllithium to the boronic ester 1a in diethyl ether at 0 °C. After solvent removal, the photocatalyst fac-Ir(ppy)₃ (1 mol%) and THF were added followed by the addition of 3a. Upon blue LED light irradiation, the mixture was stirred at room temperature for 16 hours. To our delight, the desired 1,2-aminoboronic ester 4a was obtained, albeit with low yield (26%,

The vibrational analysis and torsional study of trans-1,2-dimethylcyclopropane and cis-1,2-dimethylcyclopropane

The infrared spectra of cis-1,2-dimethylcyclopropane and trans-1,2-dimethylcyclopropane have been recorded between 4000 and 200 cm^?1 in the polycrystalline solid phase, and 4000 to 80 cm^?1 in the gas phase. The Raman spectra of these two compounds in the gaseous and liquid phases were also recorded between 3100 and 10 cm^?1. An assignment of the thirty-nine fundamental vibrations for both cis- and trans-1,2-dimethylcyclopropane is proposed, and comparisons are made with the vibrations of other similar molecules. Additionally, ten torsional transitions were observed in the far infrared and Raman spectra of cis-1,2-dimethylcyclopropane, and four transitions were observed in the spectra of the trans compound. From these spectral data, torsional barriers were determined. The effective barriers to methyl torsion are 2.92 kcal mol^?1 (12.20 kJ mol^?1) for cis-1,2-dimethylcyclopropane and 2.61 kcal mol^?1 (11.14 kJ mol^?1) for trans-1,2-dimethylcyclopronane.     

Hydroborierung von 3-methyl-1,3-butadien mit 1,2:1,2-bis(tetramethylen)diboran(6)

The nature of the hydroboration product obtained from 3-methyl-1,3-butadiene and 1,2 : 1,2-bis(tetramethylene)diborane(6) (1) allows for the discussion of the reaction mechanism. The hydroboration proceedsby retention of the cyclic structure in the first step, followed by exchange of BH and BC bonds and final cyclic hydroboration to give 1-(boracyclopentyl)-4-(3-methylboracyclopentyl)butane (5). The structural assignment of 5 is based on ¹H, ¹¹B and ¹³C NMR data.     

1,2-oxazine chemistry—IV : The conformational equilibria in 2,5- and 2,4-dimethyltetrahydro-1,2-oxazines

The synthesis of 2,5-dimethyltetrahydro-1,2-oxazine via 5-methyldihydro-1,2-oxazine and the preparation of a pure sample of 2,4-dimethyltetrahydro-1,2-oxazine are reported. For the 2,5-dimethyl derivative low temperature (?40° to ?45°) ¹H NMR measurements show signals from the trans (95%) and cis (5%) conformations. From this result it follows that an axial 5-Me group in a tetrahydro-1,2-oxazine ring is 5·7 ± 0·4 kJ mole^?1 less stable than when equatorial. Low temperature measurements on the 2,4-dimethyl derivative fail to show any sign of the conformation with an axial Me group. These results in conjunction with earlier relative free energy difference measurements, give the following conformational free energy differences for Me groups on ring C atoms; C(4) 7·1 ± 1·0; C(3) 7·9 ± 0·8; C(6) 10·1 ± 1·6 kJ mole^?1.     

Conformational study of 1,2-dithiacyclononane

The temperature dependence of the Raman spectrum of 1,2-dithiacyclononane (1,2-DTCN) in the SS stretching region has been used to infer the existence of a conformational equilibrium with ΔH⁰ = 5.0 ± 0.8 kJ/mol. Molecular mechanics calculations predict a (2 2 5)-C₂ lowest energy conformation in equilibrium with a (2 3 4) structure. The fully decoupled ¹³C NMR spectrum at −80°C and the Raman spectra are consistent with this postulate. The temperature dependence of the ¹H NMR spectrum of 1,2-DTCN is characteristic of the ring inversion process. A crude lineshape analysis allows us to calculate ΔG⁰ = 49.0 ± 1.2 kJ/mol.     

Synthesis and physicochemical studies on 1,2-bisazolylethanes

Twenty symmetrical and asymmetrical 1,2-bisazolylethanes have been obtained from azoles and 1,2-dibromoethane or 1-chloro-2-(pyrazol-1-yl)ethane by phase transfer catalysis (PTC). The ¹H and ¹³C nmr properties are reported and the chemical shifts of the ethylene carbon atoms discussed using an additive model.     

Herstellung von Argininpeptiden mitN 7,N 8-(1,2-Dihydroxycyclohex-1,2-ylen)-Schutz

A method for the synthesis of arginine peptides is described, in which the side chain guanidine function is blocked through reaction with 1,2-cyclohexanedione in borate buffers.Coupling to the carboxyl group of arginine was achieved by active ester, by dicyclohexylcarbodiimide/1-hydroxybenzotriazole¹, and by the mixed anhydride methods². Neither lactam formation nor acylation of the vicinal hydroxyls of the N⁷, N⁸-(1,2-dihydroxycyclohex-1,2-ylene) guanidino group was observed.Removal of the protecting group is strongly influenced by steric factors. Some side reactions observed during modification of peptides and protein fragments with 1,2-cyclohexanedione are also described.

Herrn Professor Dr.Hermann Stetter zum 65. Geburtstag gewidmet.     

Kinetics of the pyrolysis of 1,2-diiodoethylene

The spectrophotometric determination of the rate of pyrolysis of 1,2-diiodoethylene from 305.8 to 435.0° (with additional data on the addition of iodine to acetylene from 198.1 to 331.6°) has resulted in the observation of both a (in part heterogeneous) unimolecular process (A), and an iodine atom catalyzed process (B). For the homogeneous unimolecular process, log (k_A/sec^?1) ≈ 12.5–46/θ would appear to be reasonable, while log (k_B/M^?1 sec^?1) = 11.8–23.9/θ, where θ = 2.303RT in kcal/mole. It is suggested that a donor–acceptor complex intermediate may explain the observed rate constant of process B and analogous reactions in other systems.     

Metallkomplexe eines 1-Oxo-1,2-diphosphacyclopentanons

Coordination Compounds with an 1-Oxo-1,2-diphosphacyclopentanone 1-Oxo-1,2-diphosphacyclopentanone ( 2 ) is a ligand with three different sites for typical coordination. Thus seven types of structural different coordination compounds as well as salts can be received: 2 -W(CO)₅; ( 2 -SbCl₃)₂; 2 ^(–)-Cu⁽²⁺⁾- 2 ^(–); 2 ^(–)-Co⁽³⁺⁾(H₂O) · (OH)- 2 ^(–); (CO)₅W- 2 ^(–)-Cu⁽²⁺⁾- 2 ^(–)-W(CO)₅; (CO)₅W- 2 -SbCl₃; Cl₃Sb- 2 ^(–)-Cu⁽²⁺⁾- 2 ^(–)-SbCl₃; Cl₃Sb((CO)₅W)- 2 ^(–)-Cu⁽²⁺⁾-2^(–)-(W(CO)₅)SbCl₃; [Cu(en)₂(H₂O)₂]²⁺ ( 2 ^(–)); [Cu(en)₂(CH₃OH)₂]²⁺ [ 2 ^(–)-W(CO)₅]₂; NR₄⁽⁺⁾ 2 ^(–)     

Synthesis of 1H-imidazo[1,2-a]imidazole

The synthesis and structure analysis of the unknown 1H-imidazo[1,2-a]imidazole ( 1 ) is described. The preparation involves alkylation of 2-aminoimidazole with bromoacetaldehyde diethyl acetal and subsequent hydrolysis and cyclization with hydrochloric acid. The structure was characterized by mass spectrometry and by ¹H-, ¹⁵N- and ¹³C-nmr of 1 and by ¹H-nmr of its 1-benzyl derivative 8 . An independent synthesis of 8 was accomplished via cyclization of 2-(N-dichloroethyl-N-benzyl)aminoimidazole ( 11 ).     

A Reductive 1,2 Transposition of Acyclic Ketones

Earlier we noted that the hydroboration of the trimethylsilyl enol ether of an acyclic ketone results in an elimination of a trimethylsiloxyborane moiety with the subsequent formation of an olefin.^1,2 The olefin formed then undergoes hydroboration giving a monoalcohol upon oxidation. (eq 1) We wish to report here on the utility of this sequence, illustrated in eq 1, in the reductive 1,2 transposition of acyclic ketones.³     

Quantum chemical approach to isomerization of 1,2-dihydro-1,2-epoxybenzene and its derivatives involving hydration

The present study compares experimental values of log(10⁴ × k₀) or log k_H in the isomerization of 1,2-dihydro-1,2-epoxybenzene and its derivatives with the activation parameters by the PM3 calculation in the gas phase and a simple model of hydration which includes only water molecules linking directly to the solute. The calculated results show that none of the activation parameters in the gas phase can explain the experimental rate constants, while the enthalpies in the simple model of hydration are capable of adequately reproduce their differences. Although the hydration to the lone pairs of oxygens (21.2–22.3 kcal mol⁻¹) comprises the main part of the total hydration effect (34.1–42.8 kcal mol⁻¹) and the weak hydration to the apolar parts comprises smaller part, the latter determines the relative rates of the isomerization.     

Bis(1,2‐diselenoquadratato)metallate

Bis(1,2‐diselenosquarato) Metalates A series of 1,2‐diselenosquarato metalates [M(dssq)₂]^2– (M = Pd²⁺, Pt²⁺, Cu²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Pb²⁺, VO²⁺) was available by direct synthesis from the appropriate metal salt with dipotassium 1,2‐diselenosquarate in deoxygenized water under an argon athmosphere. The copper(II)complex, [Cu(dssq)₂]^2–, and the oxovanadium(IV)complex, [VO(dssq)₂]^2–, were identified in solution by EPR spectroscopy (parameters: [Cu(dssq)₂]^2–: g₀ = 2.073; a = –76.0 · 10^–4 cm^–1, a = 47.0 · 10^–4 cm^–1; [VO(dssq)₂]^2–: g₀ = 1.986; a = 74.9 · 10^–4 cm^–1). The complexes bis(tetraphenylphosphonium)[bis(1,2‐diselenosquarato)nickelate(II)], (Ph₄P)₂[Ni(dssq)₂], and bis(tetraphenylphosphonium)[bis(1,2‐diselenosquarato)zincate(II)], (Ph₄P)₂[Zn(dssq)₂], were characterized by X‐ray structure analysis. The square‐planar Ni^II complex (Ph₄P)₂[Ni(dssq)₂] crystallizes in the monoclinic spacegroup P2₁/n with the unit cell parameters a = 11.1472(8) Å, b = 15.331(1) Å, c = 14.783(1) Å, β = 94.441(1)° and Z = 2. The Zn^II‐complex (Ph₄P)₂[Zn(dssq)₂] is tetrahedral coordinated and crystallizes in the monoclinic spacegroup P2₁/c with the unit cell parameters a = 9.4238(1) Å, b = 18.5823(3) Å, c = 29.5309(5) Å, β = 96.763(1)° and Z = 4.     

1,2-Bis-[(5-methyl/chloro/nitro)-2-1H-benzimidazolyl]-1,2-ethanediols and their PdCl2 complexes

1,2-Bis-[(5-methyl)-2-1H-benzimidazolyl]- (L ¹), 1,2-bis-[(5-chloro)-2-1H-benzimidazolyl]- (L ²), 1,2-bis-[(5-nitro)-2-1H-benzimidazolyl]-1,2-ethanediol (L ³) and their PdCl₂ complexes were synthesized and characterized by elemental analysis, molar conductivity, i.r. and ¹H-n.m.r. spectra. The benzene ring substituents lead to a decrease in melting point. The methyl group reduces the solubility and the acidity of L ¹ and Pd(L ¹)Cl₂, whereas the Cl and NO₂ groups increase the solubility and the acidity of L ², L ³, Pd(L ²)Cl₂ and Pd(L ³)Cl₂. In Pd(L ¹)Cl₂ and Pd(L ²)Cl₂ complexes, the ligands act as a bidentate through two nitrogen atoms. In Pd(L ³)Cl₂, ligand coordination occurs through one OH group oxygen atom and one of the benzimidazole nitrogen atoms.     

Penetration of sodium cetylsulfate into monolayers of 1,2-dipalmitoyl- and 1,2-dimyristoyl-phosphatidylethanolamine

The penetration of sodium cetylsulfate into monolayers of dipalmitoyl- and dimyristoyl-phosphatidylethanolamine was studied by the measurement of surface and penetration pressures using the vertical plate method of Wilhelmy. The penetration isotherms in two systems were investigated at different initial molecular areasA _M :System I: Sodium cetylsulfate/1,2-dipalmitoyl-phosphatidylethanolamine atA _M = 0.85; 0.75; 0.65; 0.55; 0.50; 0.46 and 0.44 nm² · molecule^–1.System II: Sodium cetylsulfate/1,2-dimyristoyl-phosphatidylethanolamine atA _M = 0.85; 0.75; 0.60 and 0.55 nm² · molecule^–1.(T=295 K; substrate 0.1 M NaCl)The penetration isotherms (F _t vs. logc _s ) increase linearly atF _t > 10 mN · m^–1 in system I and atF _t >25 mN · m^–1 in system II. The isotherms of both systems are shifted to lower surfactant concentrations with decreasing molecular area of spread monolayer. A maximum of the slopes (dF_t/d logc _s )occurs at A_M=0.50 nm² · molecule^–1. This behavior is also reflected in the dependenceG _p ⁰ (free standard penetration enthalpy) and _s (relative surface excess concentration of surfactant) onA _M . These changes are related to a different packing of the compounds in the binary penetrated monolayers.In the high pressure region both system are nearly identical. Differences in the low pressure region arise from the penetration into different monolayer states.Nomenclature _M effective cross sectional area of monolayer molecule - a _M partial molecular area of monolayer molecule - a _s partial molecular area of surfactant molecule in the penetrated film - a _s ⁰ molecular area of surfactant molecule at definite film pressure (eq. (3)) - A _M molecular area of theF/A-isotherm - A _N constant in equation (2) - A _K collapse area - b penetration coefficient in equations (2); (2 a) - c _s bulk concentration of surfactant - logc _s relative shift of penetration isotherm with regard to the adsorption isotherm at constantF _t - F film pressure of monolayer component in absence of surfactant - F _t total film pressure - F _p film pressure change due to penetration - F _p,max constant in equation (1) - G _p ⁰ free standard penetration energy - k Boltzmann constant - K constant in equation (1) - R gas constant - T temperature - x _s ⁰ mole fraction of surfactant in the penetrated film - _M surface concentration of monolayer molecules - _s relative adsorption of surfactant - _w ⁰ surface concentration of surfactant in monolayer-free surface - factor in equation (6 a) - surface tension     

UV spectroscopy of monosubstituted derivatives of 1,2-dihydro-C60-fullerenes

UV spectroscopy is used to determine the molar absorption coefficients of C₆₀ fullerene and monosubstituted 1,2-dihydro-C₆₀-fullerenes in different solvents. It is found that the extinction coefficient of C₆₀ at 330 nm (the main absorption band most frequently used for qualitative and quantitative determination of the C₆₀ content) is independent of the nature of the solvent and is ～54400 M^?1·cm^?1. The molar absorption coefficients of a series of monosubstituted 1,2-dihydro-C₆₀-fullerenes are practically independent of the chemical structure and the length of the substituent and are 35700 M^?1·cm^?1 (λ ～ 328 nm) and 115250 M^?1·cm^?1 (λ ～ 257 nm). It is shown that the substitution in fullerene proceeds via the double 6,6 bond, as evidenced by the absorption band at 424 nm in the spectra of these compounds, which is characteristic of monosubstituted methanofullerenes.     

1,2-Dipyridazinyl-?then- und-?than-1,2-diole aus Pyridazin-carbaldehyden

Treatment of pyridazine-4-carboxaldehyde with catalytic amounts of KCN results in formation of pyridazine-4-carboxylic acid and two stereoisomeric diols (4,5). The configurations of4 and5 are explained on basis of the¹H-NMR-spectra, the mechanism of reaction is discussed. Pyridazine-3-carboxaldehyde (10) reacts with HCN to form the addition product of10-cyanhydrine to10 (11). HCN-elimination from11 yields the enediol12 which by oxygen is oxidized to pyridazine-3-carboxylic acid or its methyl ester.     

β-Ribo- and α-arabinonucleosides containing the 1,2-benzisoxazole and 1,2-benzisothiazole rings

The reaction of the silylated base of 1,2-benzisoxazol-3(2H)-one ( 1 ) and its 7-methyl derivative 5 and 5-methyl-1,2-benzisothiazol-3(2H)-one ( 9 ), respectively, with 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D-ribofuranose followed by basic deprotection gave the corresponding β-D-ribonucleosides, and the silylated base of 1 , when treated with 1-O-acetyl-2,3,5-tri-O-benzoyl-α-D-arabinofuranose in the presence of stannic chloride, afforded the corresponding α-arabinonucleoside. Structural proofs of these nucleosides are provided from elemental analyses and ¹H and ¹³C nmr spectra.     

Molar heat capacity of binary liquid mixtures: 1,2-dichloroethane + cyclohexane and 1,2-dichloroethane + methylcyclohexane

The molar heat capacity at constant pressure, C_P, of the two binary liquid mixtures 1,2-dichloroethane + cyclohexane and 1,2-dichloroethane + methylcyclohexane were determined at 298.15 K from measurements of the volumetric heat capacity, C_P/V, in a Picker flow microcalorimeter (V is the molar volume). For the molar excess heat capacity, C_P^E, the imprecision of the adopted stepwise procedure is characterized by a standard deviation of about ± 0.05 J K^?1 mole^?1, which amounts to ca. 3% of C_P^E. Literature data on ultrasonic velocities, on molar volumes, and on coefficients of thermal expansion were used to calculate the molar heat capacity at constant volume, C_v, and the isothermal compressibility, β_T, of the pure substances, as well as the corresponding excess quantities C_V^E and (Vβ_T)^E of the binary mixture 1,2-dichloroethane + cyclohexane. A preliminary discussion of our results in terms of external and internal rotational behavior (trans-gauche equilibrium of 1,2-dichloroethane) is presented.