Anion 1a Research Articles

Synthesis of Nitroarylalkenes via reaction of nitrobenzyl sulfones with nitronate anions

o-Nitrobenzyl tolyl sulfones (1 a – e) react with nitronate anions (2a, b) giving nitroaryl derivatives of nitroalkanes (3) which eliminate nitrous acid giving nitroarylalkenes (4a – f) as final products.

Concave reagents, 6. Can the structure of concave reagents determine selectivities?

AbstractThe concave position of the proton in protonated concave pyridines 8·H+ or 9·H+ leads to increased selectivities in protonation reactions of nitronate anions 2a–d. Thus, the reprotonation of the nitronate anion 2a by the protonated concave pyridine 8·H+ selectively yields the nitro compound 1a whereas the nitronate anions 2b–d are transformed to the Net products 4b–d.

Polarized ketene dithioacetals. Part 65. Studies on additions of 2-aroyl-3-cyano-1,1-bis(methylthio)propenide anions to hetero-multiple bonds

2-Aroyl-3-cyano-1,1-bis(methylthio)propenide anions (2a and b) undergo stepwise [3 + 2] cyclocondensation with aryl isothiocyanates followed by elimination of a methylthio group to give the corresponding 4-aroyl-2-arylamino-5-(methylthio)thiophene-3-carbonitriles (5a–c). Addition of the anion (2a)(Ar = Ph) to 4-chlorobenzaldehyde under similar conditions yielded the cyclic hemiacetal (8), which in the presence of BF3· Et2O and methanol afforded the O-methyl derivative (12) and 2-(4-chlorophenyl-3-bis(methylthio)methyl-5-phenylfuran-3-carbonitrile (13). Addition of the propenide anions (2a and c) to benzonitrile gave only dimeric products (14a and b), respectively. Mechanisms for these reactions are suggested.

Electron transfer reactions. Reaction of nitrones with potassium

Treatment of nitrones (1a–d, 26a,b, 34, 49) with potassium in tetrahydrofuran (THF) gives rise to radical anion (2a–d, 27a,b, 35, 50) and dianion intermediates (3a–d, 28a,b, 36) through electron transfer reactions. These intermediates undergo further transformations to give a variety of products. Thus, the aldehydonitrones (1a–d) give the corresponding aldehydes (10a–c), carboxylic acids (25a–c), and azobenzenes (19a,d), whereas the ketonitrones (26a,b) give deoxygenation products (31a,b). The nitrone 34 gave a mixture of products consisting of benzoic acid (25a), dibenzyl (48), the dimeric product 38, and tetraphenylpyrazine (46), whereas 49 did not give any isolable product. Cyclic voltammetric studies have been employed to measure the reduction potentials for both one-electron and two-electron transfer processes, leading to the radical anions and dianions respectively. These intermediates have been characterized through their electronic spectra and they were quenched by oxygen. Pulse radiolysis of the nitrones 1a–d, 26a,b, 34, and 49 also gave the corresponding radical anions 2a–d, 27a,b, 35, and 50, characterized by their spectra.

Formation of active oxygen species by dithranol, III. Dithranol, active oxygen species and lipid peroxidation in vivo.

AbstractAt pH 7.8 the dithranol anion 1a is oxidized in the dark to yield the bianthrone 3 besides dithranol brown, whilst O2 is reduced to O2·− and H2O2. O2·− was detected by the reduction of nitroblue‐tetrazolium (NBT, 4). The formation of the formazan 5 was inhibited by superoxide dismutase (SOD). Exclusion of O2 and addition of SOD reveal a direct electron transfer from 1a to 4 and to cytochrome c which was not affected in the presence of SOD. — In vivo experiments indicate a low rate of lipid peroxidation which was determined on the basis of ethane exhalation.

Dithranol and active oxygen species, II. 1O2‐oxidation of dithranol to Chrysazin

AbstractRaab's biochemically active species, derived from dithranol (1), is the anion 1a (Sect. A), which is a photosensitizer. Its sensitizing potency is quantitatively compared with that of rose bengal, tetraphenylporphyrine and other sensitizers (Sect. B). In Sect. C the mechanism of the conversion of 1a with 1Δg18O2 to chrysazin (2) is elucidated.

Diboriranides and a 1,3‐Diboraallyl System with BHB Bridge

The first three-membered ring anions 1a, b containing two B atoms and one C atom have been isolated as the potassium salts. Surprisingly, Protonation leads to formation of isolable H-bridged species 2 (RSiMe3, R′tBu).

Chemie der lithium-enolat-heptafulvene: regiospezifische aldol-addition

Aldehydes and ketones add to the cycloheptatriene ester anion 2a and to the carboxylic acid dianion 2b at C-7 (α-attack) or C-2 (C-5) (γ-attack), depending on the starting compounds.

Chemistry of 2H‐thiopyran and derivatives IV. Deprotonation and methylation of 2H‐thieno[2,3‐b]thiopyran and some derivatives

AbstractMetallation of 2H‐thieno[2,3‐b]thiopyran 1 by strong bases under relatively apolar conditions proceeds exclusively in the 2‐position of the thiophene ring. In polar media a 2‐proton of the thiopyran ring is removed to give the anion 1b. By addition of hexamethylphosphoric triamide (HMPT) to the lithiated compound 1a conversion into 1b takes place. The anions 1a and 1b react with methyl iodide to give the compounds 2 and 3, respectively. Compound 2 can be further methylated by reaction with BuLi in tetrahydrofuran (THF)/HMPT mixtures or sodamide in liquid NH3, followed by addition of methyl iodide. The resulting compound 4 can be converted into the compounds 5, 6 or 7, depending on the base‐solvent system: Compound 5 is produced by interaction between 4 and KNH2 in liquid NH3 at − 33°, followed by methylation at − 60°. If the reaction with KNH2 is carried out at − 60°, however, methylation gives 6, this result is also obtained from 4, BuLi in THF/HMPT and CH3I. Omission of HMPT during the metallation gives rise to vinylic proton abstraction, and subsequent addition of CH3I leads to 7.

Cation effect on the course of anionic reactions in the presence of a solid base

The formation of cyclopropanes by the MacCoy reaction is reinvestigated in the presence solid sodium or potassium hydroxide, with or without a quaternary ammonium salt, in dioxanne: ▪ With NaOH alone, the major reaction is the saponification of the α-chloro-ester 1; the cyclopropanes formation is the only reaction observed using either KOH, or the two bases with NBu + 4Br −. The saponification by NaOH is attributed to the complexation of the carbonyl group by Na +, which favours the nucleophilic attack of the hydroxide anion: ▪ The complexation is weaker with K + than with Na +, and then, the proton abstraction of the α-chloroester is predominant. These results show that metallic cations have a similar behaviour in a crystalline network and in solution. The stereoselectivity is known to be determined during the cyclisation step. The predominant formation of the Z isomer is explained by chelate formation of metal cation with the two carbonyl groups, while the E isomer is favoured when the size of the cation is too large to allow such a chelate formation. ▪ The different stereochemical results obtained by addition of the ammonium salt involve the association of the intermediate anion 2A with NBu + 4Br −.Furthermore, the condensation should occur in the organic phase with the phase transfer reagent, and on the solid surface when the bases are used alone.