Benzophenone vs. Copper/Benzophenone in Light‐Promoted Atom Transfer Radical Additions (ATRAs): Highly Effective Iodoperfluoroalkylation of Alkenes/Alkynes and Mechanistic Studies

Iodoperfluooralkylation of terminal alkenes and alkynes is effectively photo‐promoted by benzophenone 2 (BP) or the photoreducible copper(II) complex 1 . In particular, BP at 1 mol% in methanol upon 365 nm irradiation with a low‐pressure mercury lamp (type TLC=thin layer chromatography, 6 W) results in a fast reaction with excellent reaction yields. Complex 1 and BP 2 exhibited very similar reactivity, suggesting that the reactions involving 1 are likely to be governed by the benzophenone photoactivation processes, rather than copper(I)/(II) redox processes. Mechanistic investigations using transient absorption spectroscopy revealed that a deactivation pathway of the benzophenone triplet (³BP*) is via its reaction with the methanol solvent. We propose that the generated radicals, in particular ^.CH₂OH, play a key role in the initiation step forming R_f^. by reacting with R_fI, R_f^. then entering a radical chain cycle. ¹H NMR studies provided evidence that a substantial amount (∼7% NMR yield) of the hemiacetal CH₃OCH₂OH is formed, i.e., the possible by‐product of the reaction between ^.CH₂OH and R_fI. Finally, DFT calculations indicate that a triplet‐triplet energy transfer (TTET) process from ³BP* to perfluorooctyl iodide (C₈F₁₇I) is unlikely or should be rather slow under the reaction conditions, consistent with the transient absorption studies.

     

Synthese und Reaktionen chiraler,von (R)-(−)-bzw. (S)-(+)-2-Methoxymethylpyrrolidin abgeleiteter Dithiocarbamate

Synthesis and Reactions of Chiral Dithiocarbamates Derived from (R)-(−)- or (S)-(+)-2- The synthesis, diastereoselective alkylation reactions, dithiocarboxylation, and aldol condensation of several substituted methyl (R¹ CH₂) (S)-2-(methoxymethyl)-pyrrolidine-1-dithiocarboxylates (S)- 2 and of the corresponding (R)-derivatives (R)- 2 are described. The new enantiomeric dithiocarbamates (S) -2a – e , and (R) -2a – d are obtained by reaction of (S)-(+)-[(S) -1 ] or (R)-(−)-2-(methoxymethyl)-pyrrolidine [(R) -1 ], respectively, with carbon disulfide in dry methanol/anhydrous sodium acetate and the appropriate alkylating agent. The cyclic ketene dithioacetals (S) -3 and (R) -3 are formed by dithiocarboxylation procedure of (S) -2a and (R) -2a whereas (S) -6 and (R) -6 are obtained by aldol reaction with isobutyraldehyde. (S)- 2c , d and (R) -2c , d react in a diastereoselective manner after deprotonation with n-BuLi or LiTMP/LiBr at −78°C in THF with alkyl halides to the enantiomeric compounds 4a /ent -4a, 4b /ent -4b and 5 /ent -5 , respectively.     

Neglected Aspects of Anthracenide (Anthracenidyl) Chemistry — Reactions with two N‐Benzoylaziridines

Reaction of anthracenide A ^·‐ with N‐benzoylaziridines 1a,b forms charged radicals 3a,b by single electron transfer and homolytic ring opening. Reactions follow that are known or expected as e.g. coupling with position 9 of A ^·‐ forming dihydroanthracene anions 9a,b that yield amidoethylated dihydroanthracenes 10a,b , or react with 1a,b giving finally 9,10‐bis‐amidoethylated dihydroanthracenes 11a,b . Results depend on experimental conditions and on the counter ions Na⁺ or Li⁺. Coupling is not regiospecific: contributions by positions 2 and 1 reach 29% or 4%, respectively, of total coupling with the primary radical 3a ; much higher contributions are possible with Li. Product 21s (probably 3,3′‐disubstituted tetrahydrobianthryl) may arise by hydrogen detachment from the first intermediate ( 29 ) of coupling with position 2 and dimerization of the formed 2‐substituted A ^·‐ ( 30 ). Coupling products may be fully aromatized or may be hydroxylated in one of the benzylic positions. With counter ion Li⁺ a non‐SET reaction of 1a with the dimer of A ^·‐ is indicated by the isolation of 9‐benzoyl‐dihydroanthracene 15 and by 19% yield of 16a (aromatized 10a ). Reaction of 3b with anthracene is indicated by 10,10′‐disubstituted tetrahydrobianthryl 37 .     

Flash photolysis investigation on primary processes of the sensitized polymerization of vinylmonomers. III. Photoreactions of benzoin compounds and stationary polymerization experiments

Benzoin (B), benzoinacetate (BA), benzoinmethylether (BME) and benzoinisopropylether (BIPE) were irradiated at room temperature in benzene solution in the presence of styrene (St), methyl methacrylate (MMA), vinylacetate (VAc) or acrylonitrile (AN). Flash photolysis experiments at λ=347 nm yielded (a) rate constants k_q (in 1 mol^-1s^-1) of the reaction between excited sensitizers and monomers: 8·10⁹ (B/St), 5·10⁸ (B/MMA), 5·10⁹ (BA/St), 8·10⁸ (BA/MMA); (b) rate constants K^R.+M (in 1mol^-1 s^-1) of the reaction between sensitizer radicals and monomers: about 1.5·10⁵ (BME/St, BME/VAc, BA/VAc, B/VAc), 9· 10⁴ (BME/MMA), 2·10⁴ (BME/AN). The reaction R·+M caused in certain cases (B/St, B/VAc, BME/St) the formation of an additional optical absorption after the flash. Stationary irradiations at λ>320 nm of monomer solutions (5mol/1) showed that BA is least effective. Rates of polymerization increased in the series BA<B<BIPE<BME. For the systems containing St or MMA it was found that ?_i=_i+0.6α_R (?_i=quantum yield for the initiation of kinetic chains, α_R =fraction of triplets converted to radicals). The fraction of radicals starting kinetic chains is ca. 0.3 in these cases.     

The kinetics of reduction of selenious(IV) ions in hydrochloric acid with sulphur dioxide

The reduction of selenious ions to its elemental state has been found to be a function of selenious ion concentration, solution acidity, gas flow rate and temperature. The rate equation can be written as: where α = ?1/2, β = 1, γ = 0.9, E = ?53 411 kJ kg^?1mol^?1, R = 8314 kJ kg^?1 mol^?1 K^?1 and k₀ = 194. The reaction temperature starts to decrease when the conversion rate reaches a maximum. This observation can be used to determine the end of the reaction.     

Synthese von cyclischen N,O- bzw. N,S-Heterocyclen durch Kondensation von Fettsäurealkylolamiden mit Carbonylverbindungen bzw. Phosphorpentasulfid

Synthesis of Cyclic N,O- and N,S-Heterocyclic Compounds by Condensation of Fatty Acid Alkylolamides with Carbonyl Compounds and Phosphorous Pentasulfide Respectively Fatty acid alkylolamides of the type RCONHCHR¹ (CH₂)_n CHR₂OH (R: alkyl rest with 2 to 17 carbon atoms, cycloalkyl or aryl rest; R₁ and R₂: alkyl rests with 1 to 3 carbon atoms or hydrogen; and n = 0–2) are converted by acidic condensation with lower aliphatic or aromatic aldehydes and ketones respectively to mono- and disubstituted N-acyl-oxazolidines, N-acyl-1,3-tetrahydrooxazines and N-acyl-1,3-hexahydrooxazepines. Furthermore, new types of 2-alkyl-4,5-dihydro-6H-1,3-thiazine (n = 1) besides monoalkyl substituted Δ-2-thiazolines (n = 0) were obtained from fatty acid alkylolamides by condensation with P₂S₅. A large number of the compounds prepared show excellent bacteriostatic and fungistatic action.     

Coordination modes in zirconium β-diketiminate complexes

Reaction of β-diketiminate lithium salts, nacnac^RLi(THF) (R = 2,6-xylyl (1a), R-CH(Me)Ph (1b)), with ZrCl₄ or ZrCl₄·THF yielded the mono-diketiminate complexes nacnac^RZrCl₃(THF), 2a and 2b. Complex 2a did not react further with a second equivalent of 1a, but with CpLi or IndLi to form pseudo-tetrahedral complexes 3 and 4. No product could be isolated from reaction of 2b with CpLi. Coordination of the diketiminate ligand in 2a is best described as a distorted κ²-, in-plane coordination. Complexes 3 and 4, however, display a haptotropic shift of the diketiminate ligand and its coordination is best described as κ²,η²-coordination. Although not previously described, analyses of available structures in the literature reveal that non-symmetric κ²,η²-coordination is an independent coordination mode, which exists next to the previously described “η⁵-like” coordination.     

Perfluoroalkanesulfonylation of Alkynyl(phenyl)iodonium Tosylates by the Weakly Nucleophilic Sodium Perfluoroalkanesulfinates

An additive‐ and transition metal‐free perfluoroalkanesulfonylation of alkynyl(phenyl)iodonium tosylates with sodium perfluoroalkanesulfinates (R_fnSO₂Na) is described. The poorly nucleophilic R_fnSO₂Na reacted with alkynyl(phenyl)iodonium salts in dichloromethane at room temperature under a nitrogen atmosphere for 5–60 minutes to afford a variety of acetylenic triflones and alkynyl perfluoroalkyl sulfones in good to quantitative yields. The position of substituents on the phenyl rings of the arylethynyl moiety in the iodonium salts had a big influence on the reaction. The formation of five‐membered cyclic vinyl sulfones suggested that the reaction proceeds via an alkylidene carbene intermediate. Furthermore, successful scaling‐up of the reaction demonstrates the practicality of the new method. Advantages of the method include short reaction times, mild conditions, and the easy access to perfluoroalkanesulfonylation reagents (R_fnSO₂Na).

     

Selectivity in the Oxidation of Aliphatic Ketones by thallic sulphate in aqueous medium

The effects of temperature, structure and sulphuric acid concentration on the selectivity of the oxidation of aliphatic ketones (R¹COR²) ( 1a – g ) by thallic sulphate have been investigated. With increasing temperature the quantity of internal α-hydroxyketone ( 3a – d ) decreases and the quantity of 1-hydroxyketone ( 2a – d ) increases in the oxidation of methyl alkyl ketones (R²>CH₃) ( 1a – d ). The same concerns to the oxidation products of hexan-3-one ( 1e ): 2-hydroxy-hexan-3-one ( 2e ) and 4-hydroxy-hexan-3-one ( 3e ), respectively. “The inverse selectivity temperature” (IST) for oxidation of linear methyl alkyl ketones ( 1a – c ) and hexan-3-one ( 1e ) has been found. With the use of the linear free-energy relationship it has been found that the selectivity of the reaction decreases with increasing the polar and steric effects of substituents R¹, R². With increasing the sulphuric acid concentration the selectivity of the oxidation of methyl alkyl ketones ( 1a , 1d ) increases.     

Radikalreaktionen an N-Heterocyclen. XI [1] Reaktionen von 3-Methyl-pyrazolin-5-onen mit Phenoxyl-Radikalen

Free Radical Reactions of N-Heterocyclic Compounds. XI. Reaction of 3-Methyl-pyrazolin-5-ones with Phenoxy Radicals Pyrazolin-5-ones ( 3a–i ) were oxidized with 2,4,6-trisubstituted phenoxy radicals ( 2a–d ) to the corresponding radicals ( 4a–i ), which dimerised or combined with phenoxy radical ( 2a ) depending on the R¹- and R⁴-substituents in ( 3 ). In the case of 3-methyl-1-phenyl-pyrazolin-5-one ( 3f ) the primary radical combination products were not found, but the corresponding quinone methide ( 17 ) and the o-phenol derivative ( 18 ) were isolated. Products and yields have been investigated as a function of mol ratio substrate: oxidant and solvent. The radical combination products ( 7–10 ) could de-tertbutylated in the presence of aluminium chloride or in the presence of trifluoroarcetic acid, forming heterocyclic substituted phenols ( 21 ) and ( 22 ).     

Electrochemical oxidation of aryl cycloheptatrienes

The electrochemical oxidation of various substituted aryl cycloheptatrienes and cyclohepta‐1,3,5‐triene, the parent compound, in acetonitrile is investigated with the aid of cyclic voltammetry (CV), experiments at the rotating ring disk electrode (RRDE) and controlled potential electrolysis. 1‐(p‐methoxyphenyl)‐cycloheptatriene 2c , 1‐ and 3‐(p‐di‐methylaminophenyl)‐cycloheptatriene 2d , 3d are converted by anodic oxidation into the radical cations the main reaction of which is not the deprotonation. According to the proposed mechanism the electrochemical oxidation proceeds along the radical cation dimerization. The dimer cations ( 1 ₂²⁺) decompose under deprotonation into tropylium ions 4 and starting compound. In the case of 1‐(p‐dimethylaminophenyl)‐cycloheptatriene 2d the deprotonation reaction can compete with the dimerization. The oxidation of the cycloheptatriene compounds is kinetically controlled by the homogeneous chemical steps rather than by the initial electron transfer.     

Photochemie und Photophysik von 3-(2-Isoxazolinyl)-phenylketonen

Photochemistry and Photophysics of 3-(2-Isoxazolinyl)-phenylketones 3-Benzoyl-Δ²-1,2-oxazolines ( 1–6 ) are formed by 1,3-dipolar cycloaddition between benzoylnitril-N-oxide ( 8 ) and dihydrofurane 9 or 1,3-dioxep-5-enes ( 10a–c ). The preparative yields are small due to the competitive dimerization of the dipole 8 . Two stereoisomers are obtained by using 2-substituted 1,3-dioxep-5-enes as dipolarophiles. The different steric position of the substituents in 3–6 gives rise to different spectral data. The synthesized ketones possess triplet states with a high degree of charge transfer character. Therefore, the ability to H-abstraction reaction from alcohols is small. For ketone 2 and methanol as H-donor a rate constant of k = 4,1 · 10² M⁻¹s⁻¹ is determined. Also by electron transfer reactions with triethylamine and some onium compounds the reactivity of the T₁ of the ketones 1–6 is less compared to those of nπ* excited ketones. The photolysis of the ketones takes place very unselectively and leads to a product mixture. The quantum yields for the decay of the ketones are 10⁻² to 10⁻³.     

Cerebrosides from a Far‐Eastern Glass Sponge Aulosaccus sp.

Nine new cerebrosides 1a–d , 2a , 2b , 3a–c were found in the extract of a Far‐Eastern glass sponge Aulosaccus sp. (class Hexactinellida). These β‐d ‐glucopyranosyl‐(1 → 1)‐ceramides contain sphingoid bases (2S,3S,4R,11Z)‐2‐aminoeicos‐11‐ene‐1,3,4‐triol (in 1a – d ), (2S,3S,4R,13Z)‐2‐aminoeicos‐13‐ene‐1,3,4‐triol (in 2a , b ) and (2S,3S,4R,13S*,14R*)‐2‐amino‐13,14‐methylene‐eicosane‐1,3,4‐triol (in 3a – c ), which are N‐acylated by (2R,15Z)‐2‐hydroxydocos‐15‐enoic (in 1a , 2a , 3a ), (2R,16Z)‐2‐hydroxytricos‐16‐enoic (in 1b , 2b , 3b ), (2R,17Z)‐2‐hydroxytetracos‐17‐enoic (in 1d ) and (2R)‐2‐hydroxydocosanoic (in 1c , 3c ) acids. The monoenoic and cyclopropane‐containing sphingoid bases of compounds 1a–d , 2a , 2b , 3a–c have not been found previously in any sphingolipids. The structures of the cerebrosides were elucidated on the basis of ¹H‐, ¹³C‐NMR spectroscopy, mass spectrometry, optical rotation data and chemical transformations. A simplified method for the assignment of the absolute configuration of 2‐hydroxy fatty acids by GC analysis of their (2R)‐ and (2S)‐oct‐2‐yl esters was proposed.     

Photocleavage of plasmid DNA by dibenzothiophene S-oxide under anaerobic conditions

The ability of dibenzothiophene S-oxide (1) to photochemically induce strand breaks in plasmid DNA was studied under anaerobic conditions. DNA cleavage is monitored by the conversion of closed circular pUC19 DNA (form I) to the nicked (form II) and linear forms (form III) using densitometer digital imaging of ethidium stained gels. In buffered aqueous–acetonitrile (9:1) solutions the single-strand cleavage is efficient and does not require an alkaline reaction workup. Photodeoxygenation of 1 in buffered aqueous–acetonitrile (9{:}1) solutions containing benzene led to the production of phenol. The effect of solvent deuteration does not support the involvement of ¹O₂ from a sulfoxide dimerization reaction nor a sensitized photooxygenation reaction. The results are interpreted in terms of a sulfoxide photodeoxygenation via oxygen atoms [O(³P)] where oxidation of DNA can lead to single-strand breaks. Since the reaction of O(³P) atoms with water itself is endoergic, we propose that hydroxyl radicals do not intervene in the DNA cleaving reaction.     

Controlling Stereoselection in Aza-Cope-Mannich Reactions

The synthesis of 2-substituted cis-octahydroindolones from the reaction of cis-2-amino-1-alkenylcyclopentanols with aldehydes was studied to examine whether stereoselection in the aza-Cope–Mannich reaction could be controlled by the nature of the nitrogen substituent. 2-Alkylamino-1-(1-phenylethenyl)cyclopentanols 7 and 8 , which contain nitrogen substituents of widely differing size (Me and CHPh₂), were condensed with four aldehydes to give oxazolidines 9a–d and 10a-c. Rearrangement of these intermediates at 23–60 °C, in the presence of 0.9 equiv of (±)-10-camphorsulfonic acid in acetonitrile, gave cis-octahydroindolones 11a-d and 12a–c in yields of 77–95%. Using a combination of single-crystal X-ray crystallography, ¹H nOe measurements, and comparisons with known materials it was established that the N-methyl oxazolidines 9a–d provided exclusively cis-octahydroindolones having the 2-substituent trans to the angular substituents, while N-benzhydryl analogs 10a–c provided exclusively the all-cis products 12a–c. These results are interpreted to mean: (1) When the nitrogen substituent is small (Me), the stereochemistry-determining [3,3]-sigmatropic rearrangement occurs preferentially through a transition-state topography having the R² substituent oriented quasiequatorially ( 14 → 15 → 16 ); (2) When this substituent is large (CHPh₂), destabilizing steric interactions between the vicinal R¹ and R² substituents causes the rearrangement to occur preferentially through the alternate iminium ion stereoisomer ( 17 → 18 → 19 ).     

An electrochemical alternative strategy to the synthesis of β-lactams: Part 2 [1]. C3C4 bond formation

Electrochemically induced synthesis of β-lactams, by cyclization (via C3C4 bond formation) of haloamides XCHR¹CONR²CHR³R⁴ (X: Br, Cl), has been achieved in suitable solvent-supporting electrolyte solutions previously electrolyzed under galvanostatic control. The yields and the stereochemistry of the process are affected by the nature of substituents R¹-R⁴ and of solvent-supporting electrolyte solutions and by the electrolysis conditions.     

Highly Efficient Catalytic Dimerization of Styrenes via Cationic Palladium(II) Complexes

A highly efficient head‐to‐tail dimerization of a styrene was developed using a cationic palladium(II)‐catalyzed selective C C bond forming reaction. The complex [AllylPd(PPh₃)]⁺OTf⁻, which is believed to generate ‘palladium hydride’ (Pd H), catalyzed the dimerization of various styrenes in excellent yields as single isomers. This Pd(II)‐catalyzed reaction provides a new economical C C bond forming method.

     

Fourier Transform-EPR Spectroscopy of Electron Transfer from Excited State of Chlorophyll and Porphyrin to Duroquinone

Electron transfer reactions between the photoexcited triplets of several porphyrin and chlorophyll precursors, ³P (electron donors), and neutral duroquinone, DQ (electron acceptor), were studied by selective laser excitation-Fourier transform (FT)-EPR spectroscopy. Four different P, which are related to the photosynthetic apparatus, were examined in ethanol solutions at −243 K: pyrochlorophyll a (pChla), zinc-pyrochlorophyll a (ZnpChla), zinc-tetraphenylporphyrin (ZnTPP), and magnesium-tetraphenylporphyrin (MgTPP). This highly time-resolved EPR spectroscopy (∼10 ns delay time, ẗd, between the laser excitation and the detection pulse) permits differentiation between the various CIDEP mechanisms, i.e., triplet mechanism (TM) and radical-pair mechanism (RPM), associated with the electron transfer process. The spectra of the DQ^.− generated by the different triplet precursors strongly depend on two inherent parameters characteristic of the molecular system: (1) the zero-field splitting (ZFS) and the selective singlet-triplet (Ti l̊ S₁) population rates, A_i (i = x, y, z); (2) the difference in g-values and hyperfine components between the donor and acceptor radicals. Since the differences in g-values and hyperfines are very nearly the same in all four P^.+-DQ^.− systems examined, the different results, particularly in the time range 10 ns < ẗ<_d < 300 ns, are attributed to triplet spin memory transfer via TM. A quantitative spectral analysis is presented to describe the time evolution FT-EPR spectra. This method is used to determine the following dynamic processes: (1) spin lattice relaxation rates of the triplet precursors in solution; (2) donor-acceptor electron transfer reaction rates; (3) spin lattice relaxation rates of the acceptor radical.     

Synthesis, characterization and biological activity of dimethyltin dicarboxylates containing germanium

A series of diorganotin dicarboxylates of the general formula (CH₃)₂Sn(OCOCHR³CHR²GeR¹)₂ where R¹=(C₆H₅)₃, (P-CH₃C₆H₄)3, N(CH₂CH₂O)₃, R²=C₆H₅, H, CH₃, P-CH₃OC₆H₄, P-ClC₆H₄, P-CH₃C₆H₄, R³=CH₃ and H, have been synthesized by the reaction of dimethyltin oxide with germanium substituted propionic acid in 1:2 molar ratio in toluene. The H₂O formed was removed azeotropically using a Dean and Stark apparatus. All the compounds have been characterized by IR, multinuclear (¹H, ¹³C, ¹¹⁹Sn) NMR, mass and Mössbauer spectroscopies. All compounds were found to have potential activity against bacteria.     

Efficient Syntheses of (Thio)phosphonylated Isobenzofurans by Tandem Nucleophilic Addition and Regioselective 5‐exo‐dig Addition to Carbon‐Carbon Triple Bond: Cooperative Effect to 1,8‐Diazabicyclo[5.4.0]undec‐7‐ene (DBU)

The tandem nucleophilic addition‐cyclization reaction of o‐alkynylbenzaldehydes or o‐alkynylacetophenones 2 with dialkyl phosphites or dialkyl phosphonothioates 1 took place very smoothly in the presence of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) in THF at room temperature. In all cases, the reaction proceeded in a regioselective manner leading to the 5‐exo‐dig products 3 in excellent yields. The phenomenon of a 1,5‐sigmatropic hydrogen shift or a 1,5‐sigmatropic methyl shift was observed in this reaction depending on the different substituent groups such as R³ in the o‐alkynylbenzaldehyde or o‐alkynylacetophenone 2 substrates.