2. Internationale Konferenz iiber Methoden der Darstellung and Aufbewahrung markierter Verbindungen

Es wurde die Verteilung von ¹³¹J im Zeitraum von 1/2–24 h nach einer einmaligen Röntgenbestrahlung mit 0,21 C/kg verfolgt, wobei das Radiojod zu zwei verschiedenen Zeitpunkten nach der Exposition verabreicht wurde; 2 Stunden nach der Exposition bei der Gruppe T₂ und 18 Stunden bei der Gruppe T₁₈. Unterschiede in der Verteilung des Radiojods bei den Kontroll- und Versuchstieren weisen auf pathophysioloyische strahlenbedingte Organveränderungen hin.     

Superacidic activation of quinoline and isoquinoline; their reactions with cyclohexane and benzene(1)

Quinoline (1) and isoquinoline (2), upon activation by strong acids, lead to intermediate N,C-diprotonated dications, which are involved in reactions with weak nucleophiles. Thus, 1 and 2 undergo selective ionic hydrogenation with cyclohexane in CF3SO3H-SbF5, HBr-AlBr3-CH2Br2, or HCl-AlCl3-CH2Cl2 acid systems to give their 5,6,7,8-tetrahydro derivatives. They also readily condense with benzene in the presence of HBr-AlBr3 or HCl-AlCl3 to provide 5,6,7,8-tetrahydro-5,7-diphenylquinoline (10) and 5,6,7,8-tetrahydro-6,8-diphenylisoquinoline (12), respectively.     

Secododecahedradienes – Syntheses,Reactivity, in‐Plane Homoconjugated 3C/2e Cations, 4C/3e Radical Cations,and σ‐Bishomoaromatic 4C/2e Dications?

Secodecahedradiene 2a , featuring very proximate, perfectly syn‐periplanar and significantly pyramidalized C=C bonds, was synthesized as testing object for in‐plane(σ)‐homoconjugational electron delocalization, starting from the available pagodane 15b . The response of 2a (and in part its diester 2b ) – in π,π‐distance (average 3.08 Å), olefinic pyramidalization (average 26.9°), and π,π‐split (PE, 1.15 eV) intermediate between disecododecahedradiene 1a and 1,16‐dodecahedradiene 3a – to selected 4π‐reagents, electrophiles, and radicals was explored experimentally and by calculations. Intriguing multistep reaction sequences attest to the ease of competing stabilization pathways for the 3C/2e in‐plane homoconjugated cationic intermediates. PE, CV, and ESR measurements and calculations (DFT) characterize the radical cation generated from 2a as in‐plane homoconjugated 4C/3e‐species 2a ^.+, persistent in a Freon matrix, but only very shortly existent in solution (CIDNP). Consequently, NMR control of the two‐electron oxidation in SbF₅/SO₂ClF did not disclose the σ‐bis‐homoaromatic dication 4C/2e (see 2a ^{2 +} ), but a bis‐allylic dication 75 as persistent species. In support of 2a ^{2 +} as intermediate, evidence is presented for very limited kinetic protection offered by the secododecahedral framework to through H‐cage σ‐homoconjugated cations.     

Studies on Reactions of Thioketones with Trimethyl(trifluoromethyl)silane Catalyzed by Fluoride Ions

Treatment of 2,2,4,4‐tetramethylcyclobutane‐1,3‐dione ( 6 ) in THF with CF₃SiMe₃ in the presence of tetrabutylammonium fluoride (TBAF) yielded the corresponding 3‐(trifluoromethyl)‐3‐[(trimethylsilyl)oxy]cyclobutanone 7 (Scheme 1) via nucleophilic addition of a CF anion at the CO group and subsequent silylation of the alcoholate. Under similar conditions, the ‘monothione' 1 reacted to give thietane derivative 8 (Scheme 2), whereas in the case of ‘dithione' 2 only the dispirodithietane 9 , the dimer of 2 , was formed (Scheme 3). A conceivable mechanism for the formation of 8 is the ring opening of the primarily formed CF₃ adduct A followed by ring closure via the S‐atom (Scheme 2). In the case of thiobenzophenones 4 , complex mixtures of products were obtained including diarylmethyl trifluoromethyl sulfide 10 and 1,1‐diaryl‐2,2‐difluoroethene 11 (Scheme 4). Obviously, competing thiophilic and carbophilic addition of the CF anion took place. The reaction with 9H‐fluorene‐9‐thione ( 5 ) yielded only 9,9′‐bifluorenylidene ( 14 ; Scheme 6); this product was also formed when 5 was treated with TBAF alone. Treatment of 4a with TBAF in THF gave dibenzhydryl disulfide ( 15 ; Scheme 7), whereas, under similar conditions, 1 yielded the 3‐oxopentanedithioate 17 (Scheme 9). The reaction of dithione 2 with TBAF led to the isomeric dithiolactone 16 (Scheme 8), and 3 was transformed into 1,2,4‐trithiolane 18 (Scheme 10).     

ipso-Nitrosation of arylboronic acids with chlorotrimethylsilane and sodium nitrite

Nitroso compounds are versatile reagents in synthetic organic chemistry. Herein, we disclose a feasible protocol for the ipso-nitrosation of aryl boronic acids using chlorotrimethylsilane–sodium nitrite unison as nitrosation reagent system.     

Organometallic chemistry : V. Protonation of acylferrocenes under stable ion conditions in fso3h-so2c1f solution

Protonation of acylferrocenes (FeCOR) in FSO₃H-SO₂CIF(SO₂) solution was studied by PMR spectroscopy. The site of protonation is found to be at the carbonyl oxygen atom. Temperature dependent PMR spectra of protonated acylferrocenes FeCROH⁺ (R = CH₃, C₂H₅, C₆H₅, OCH₃) were observed indicating intermolecular hydrogen exchange with the acid solvent system. In addition the PMR spectra of acylferrocenes in FSO₃ H-SO₂ CIF(SO₂) were found to be dependent upon the acid concentration.     

Solution behavior of iron(III) and iron(II) porphyrins in DMSO and reaction with superoxide. Effect of neighboring positive charge on thermodynamics, kinetics and nature of iron-(su)peroxo product

The solution behavior of iron(III) and iron(II) complexes of 5(4),10(4),15(4),20(4)-tetra-tert-butyl-5,10,15,20-tetraphenylporphyrin (H(2)tBuTPP) and the reaction with superoxide (KO(2)) in DMSO have been studied in detail. Applying temperature and pressure dependent NMR studies, the thermodynamics of the low-spin/high-spin equilibrium between bis- and mono-DMSO Fe(II) forms have been quantified (K(DMSO) = 0.082 ± 0.002 at 298.2 K, ΔH° = +36 ± 1 kJ mol(-1), ΔS° = +101 ± 4 J K(-1) mol(-1), ΔV° = +16 ± 2 cm(3) mol(-1)). This is a key activation step for substitution and inner-sphere electron transfer. The superoxide binding constant to the iron(II) form of the studied porphyrin complex was found to be (9 ± 0.5) × 10(3) M(-1), and does not change significantly in the presence of the externally added crown ether in DMSO (11 ± 4) × 10(3) M(-1). The rate constants for the superoxide binding (k(on) = (1.30 ± 0.01) × 10(5) M(-1) s(-1)) and release (k(off) = 11.6 ± 0.7 s(-1)) are not affected by the presence of the external crown ether in solution. The resulting iron(II)-superoxide adduct has been characterized (mass spectrometry, EPR, high-pressure UV/Vis spectroscopy) and upon controlled addition of a proton source it regenerates the starting iron(II) complex. Based on DFT calculations, the reaction product without neighboring positive charge has iron(II)-superoxo character in both high-spin side-on and low-spin end-on forms. The results are compared to those obtained for the analogous complex with covalently attached crown ether, and more general conclusions regarding the spin-state equilibrium of iron(II) porphyrins, their reaction with superoxide and the electronic structure of the product species are drawn.     

Facile synthesis of α-monofluoromethyl alcohols: Nucleophilic monofluoromethylation of aldehydes using TMSCF(SO2Ph)2

α-Fluoromethyl phenyl sulfone derivatives have been extensively employed in various reactions as versatile fluoromethylating reagents. While nucleophilic monofluoromethylations of aldehydes have been achieved using fluoromethyl phenyl sulfone or fluorobis(sulfonyl)methanes, a facile protocol under mild reaction conditions remains an ardently sought goal. We now report a feasible synthetic approach toward β-monofluorinated alcohols using α-trimethylsilyl-α-fluorobis(phenylsulfonyl)methane [TMSCF(SO₂Ph)₂, TFBSM] as a novel monofluoromethylating reagent. Initiated by a catalytic amount of fluoride, the reagent can be readily added to a variety of aldehydes providing the desired products in high yields. Computational and kinetic studies have revealed the exceptional lability of the Si–C bond in TFBSM compared with other fluoromethylsilane counterparts.