Synthesis of 1,3-disubstituted benzo[c]thiophene analogs containing benzo[b]thiophene/benzo[b]pyrrole

The synthesis of 1,3-disubstituted benzo[c]thiophene analogs incorporating benzo[b]thiophene/benzo[b]pyrrole units is described.     

Synthesis and characterization of benzo[c]thiophene analogs incorporating benzo[b]thiophene/1-hexylindole/benzo[b]furan

Synthesis of 1,3-disubstituted benzo[c]thiophene analogs incorporating heterocycles such as benzo[b]thiophene/1-hexylindole/benzo[b]furan and thiophene units is described. Optical and electrochemical studies of the benzo[c]thiophene analogs are also reported.     

Novel boracycles from 2-amino-2-methylpropan-1-ol and borane methyl sulfide: Synthesis and X-ray crystal structures

On reacting the simple 1,2-amino alcohol: 2-amino-2-methylpropan-1-ol, with borane methyl sulfide (BMS), the expected five member oxazaborolidine ring is not obtained. Instead, two polycyclic structures with trigonal boron atoms 6 and 7 were obtained, and their structure were determined by X-ray crystallography. Compound 6 was obtained in 39% yield and compound 7 was obtained in 7% yield.     

Novel synthesis of benzo[b]carbazoles

A new method was adopted for the synthesis of benzo[b]carbazoles by Claisen condensation followed by Fischer indole cyclization. Newly synthesized benzo[b]carbazoles were treated with ethanol amine in the presence of polyphosphoric acid which leads to the formation of pyrazino carbazoles. All the synthesized compounds were characterized by all spectral means.     

The antioxidant activity of wines determined by the ABTS(+) method: influence of sample dilution and time

The free radical scavenging activity of 42 Spanish commercial wines was determined using the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS⁺). The ABTS⁺ radical was generated enzymatically using a horseradish peroxidase and hydrogen peroxide. The presence of wine phenolic compounds caused the absorbance of the radical to decay at 414 nm. The measurement conditions were optimised. The total phenolic content of wines ranged from 1262 to 2389 mg l⁻¹ for red wines and 70 to 407 mg l⁻¹ for white wines, expressed as gallic acid equivalents. The phenolic content of Sherry wines was similar to that of white wines. Optimum dilutions for white and Sherry wines were set up as a function of their total phenolic content (for total phenol index, TPI<300 mg gallic acid per liter, dilution 2.5:10 to 5:10; for TPI>300 mg gallic acid per liter, dilution 1:10 to 3:10). Red wines absorb at the wavelength of measurement and dilutions between 0.35:10 and 0.1:10 are advisable. Reaction kinetics were also monitored and the antioxidant activity, expressed as Trolox Equivalent Antioxidant Capacity (TEAC), was determined at 2 and 15 min of reaction. The mean values for TEAC_2 min were 5.01±1.40 mM for red wines, 0.46±0.32 mM for white wines and 0.26±0.19 mM for Sherry wines. At 15 min, mean values were 6.93±2.41 mM for red wines, 0.67±0.47 mM for white wines and 0.26±0.19 mM for Sherry wines. The correlation coefficients were better at 2 min (r=0.9012) than at 15 min (r=0.8462) when compared with TPI. Hence, TEAC_2 min seems to be a more appropriate measure.     

Highly regioselective palladium-catalyzed direct alkenylation of thiazolo[3,2-b]-1,2,4-triazoles via CH activation

An efficient and regioselective palladium-catalyzed oxidative cross-coupling reaction between thiazolo[3,2-b]-1,2,4-triazoles and alkenes has been developed. This protocol provides easy access to a variety of functionalized thiazolo[3,2-b]-1,2,4-triazole derivatives.     

InBr3-catalyzed stereoselective synthesis of 3,4-disubstituted hexahydro-1H-furo[3,4-c]pyran derivatives

An ?,δ-unsaturated alcohol tethered with a hydroxyl group, that is, (E)-2-styrylbutane-1,4-diol (1) undergoes a smooth bicyclization with various aldehydes in the presence of 10 mol % InBr₃ and at 0 °C to afford a novel series of hexahydro-1H-furo[3,4-c]pyran derivatives in good yields with high diastereoselectivity.     

A novel method for flow injection analysis of total antioxidant capacity using enzymatically produced ABTS and biamperometric detector containing interdigitated electrode

Application of interdigitated array microelectrodes as electrochemical sensors for determination of antioxidant capacity is reported. Electrochemical measurements with interdigitated electrodes (IDE) were studied in both stationary solutions and the flow system. The method is based on biamperometric measurements using ABTS⁺|ABTS redox couple in phosphate buffer solution, pH 7.40. During analysis, the ABTS radical cation was enzymatically produced by peroxidase in a tubular flow-through reactor. The performance of bioreactor was tested at different concentrations of immobilized enzyme, ABTS and hydrogen peroxide. The influence of flow rate on proper operation of the bioreactor was also studied. The results of antioxidant activity were determined using Trolox as a standard. The applied IDE detector accomplished good sensitivity of 0.3 nA/μM of Trolox and offered linear range between 20 to 500 μM of Trolox.The comparison of results (R² = 0.9915) for antioxidant activity between spectroscopic and FIA biamperometric measurements by interdigitated electrodes confirmed the applicability of the proposed method for determination of antioxidant capacity.     

A simple approach to highly functionalized benzo[b]furans from phenols and aryl iodides via aryl propargyl ethers

A variety of mono- and disubstituted phenols are alkylated with propargyl bromide to give phenyl 2-propynyl ethers, which were further coupled with aryl iodides under Sonogashira reaction conditions to give 3-phenoxy-1-aryl-1-propyne derivatives. The latter compounds underwent an initial Claisen rearrangement followed by ring closure to give functionalized benzo[b]furans in moderate to good yields.     

Preparation of fluorine compounds of groups 13 and 14: a study case for the diagonal relationship of aluminum and germanium

The synthesis of carbaalanes of composition [(AlF)₆(AlNMe₃)₂(CR)₆] containing terminal fluorine atoms is described. The clusters have in common that the central core consists of eight aluminum and six carbon atoms. Six of the eight aluminum atoms are bearing six terminal fluorine atoms. The fluorination of (t-BuNCH₂AlH)₄ results in the formation of the aggregate (t-BuNCH₂AlF)₄. In group 14, the fluorine containing unsaturated compounds LGeF, LGeS(F), LGeSe(F), and LGeNSiMe₃(F) were prepared (LHC(CMeNAr)₂), Ar = 2,6-iPr₂C₆H₃ and Ar = 2,6-Me₂(C₆H₃)).     

BF3·OEt2-catalyzed synthesis of 1-(tetrahydropyran-3-yl)-1,3-dihydroisobenzofuran and trans-fused hexahydropyrano[3,2-c]chromene derivatives

A novel intramolecular Prins cyclization of (E)-5-(2-(hydroxymethyl)phenyl)pent-4-en-1-ol with aldehydes has been achieved using 10 mol % BF₃·Et₂O to produce 1-(tetrahydropyran-3-yl)-1,3-dihydroisobenzofuran derivatives in good to excellent yields with high selectivity. Similar type of coupling with salicylaldehydes provides the trans-fused hexahydropyrano[3,2-c]chromene derivatives in excellent yields.     

Coupling and fast decarboxylation of aryloxyl radicals of 4-hydroxycinnamic acids with formation of stable p-quinomethanes

The reaction at room temperature of 3,5-di-tert-butyl- and 3,5-di-methoxy-4-hydroxycinnamic acids 1 and 2 with the dpph radical in acetone or other non-hydroxylic polar solvents yields interesting dimeric p-quinomethanes 10-16 characterized by a broad and strong absorption in the visible region. Although the yields appear to be low to moderate (10-40%), this simple synthesis affords quinones not otherwise obtainable, which contain an unsaturated γ-lactone ring (14-16). The structures have been elucidated by interpretation of ESI-MS, FT-IR and NMR spectral data. In particular, FT-IR spectra in a KBr matrix demonstrate the quinone nature of these compounds because of the presence of strong absorption bands at 1604-1640 cm⁻¹ and allows excluding the presence of carboxylic acid groups in the molecules. Kinetic evidence and molecular structures suggest that the formation of these p-quinomethanes is best explained through an 8-8 C-C coupling of the aryloxyl radicals derived from 1 and 2 and a subsequent fast mono- or di-decarboxylation of the initial dimer by an S_E1-type mechanism. Further oxidation of the phenolic intermediates by dpph yields the final quinones.     

Tröger’s bases in the acronycine, benzo[a]acronycine, and benzo[b]acronycine series

Reaction of 11-aminoacronycine, 10-aminobenzo[a]acronycine, and 10-aminobenzo[b]acronycine with paraformaldehyde gave the corresponding Tröger’s bases 11, 14, and 16, respectively. The cytotoxic activity of those three new compounds was determined against L-1210 leukemia and KB-3-1 solid tumor cell lines, in comparison with their parent compounds, acronycine, benzo[a]acronycine, and benzo[b]acronycine.     

Synthesis of pure stereoisomers of benzo[b]thienyl dehydrophenylalanines by Suzuki cross-coupling. Preliminary studies of antimicrobial activity

Several benzo[b]thienyldehydrophenylalanines were synthesized from pure stereoisomers of the methyl ester of N-(tert-butoxycarbonyl)-β-bromodehydrophenylalanine as an extension of our previously reported method for the synthesis of dehydrotryptophan analogues to dehydrophenylalanine derivatives. The latter were obtained in high yields by N-deprotection and bromination of N,N-bis-(tert-butoxycarbonyl)-(Z)-dehydrophenylalanine using TFA and NBS. This was carried out in two steps or in a one pot procedure resulting in different E/Z ratios. These compounds were coupled under Suzuki cross-coupling conditions [Pd(PPh₃)₄, Na₂CO₃, DME/H₂O] with several boronic benzo[b]thienyl acids in good to high yields maintaining the stereochemistry of the starting materials. The best yields were obtained when the boronic acid was in position 7 of the benzo[b]thiophene and with the E isomer of the brominated dehydrophenylalanine. In some cases it was possible to increase the lower yields by changing the Pd source to PdCl₂(PPh₃)₂. A model dipeptide was prepared coupling a benzo[b]thienyldehydrophenylalanine with the methyl ester of alanine. Preliminary antimicrobial studies were performed with both isomers of one of the β, β-diaryldehydroalanines obtained. The results show that the compounds are selective and very active (very low MICs) against Gram positive bacteria (B. cereus and B. subtilis) the Z-isomer being more active. The compounds are also active against Candida albicans presenting similar MICs.     

Photochromism of diarylethene derivatives bearing a benzo[b]silole unit

Photochromic benzo[b]silole derivatives, 1-(1,1-dimethyl-2-phenylbenzo[b]silol-3-yl)-2-(2-phenylbenzo[b]thien-3-yl)perfluorocyclopentene and 1-(1,1-dimethyl-2-phenylbenzo[b]silol-3-yl)-2-(2-phenyl-1-benzofuran-3-yl)perfluorocyclopentene, were synthesized and their photochromic performance was examined in solution.     

A new synthesis of benzo[b]thiophenes utilizing an interrupted Pummerer reaction

A convenient synthesis of 3-arylbenzo[b]thiophenes utilizing an interrupted Pummerer reaction of 2-(1-arylvinyl)phenyl ethyl sulfoxides is described. Thus, treatment of these sulfoxides, which were readily prepared from 2-sulfanylphenyl ketones or 2-fluoro-5-methoxybenzaldehyde, with acetic anhydride at 100 °C afforded 3-arylbenzo[b]thiophenes in reasonable yields.     

Theoretical study of the addition and abstraction reactions of hydroxyl radical with uracil

The addition as well as abstraction reactions of hydroxyl radical (OH) with the nucleic acid base, uracil (U), in the gas phase has been explored at the B3LYP/6-31+G(d,p) level of density functional theory (DFT). The energy barrier of the OH addition to both the C5 and C6 positions of the uracil is less than 1 kcal/mol while the hydrogen abstractions (H-abstractions) from either the N1 or the N3 positions are ∼9.5 kcal/mol. Further the energetics of these reactions are assessed by applying the effect of aqueous medium through the polarizable continuum model (PCM). Both the gas and the solution phase data established that the thermodynamic and kinetic factors are more favorable for the OH addition to either C5 or C6 positions of the uracil than the H-abstraction reactions. Moreover, calculations at the MPW1K/6-31+G(d,p), CCSD(T)/6-31+G(d,p)//B3LYP/6-31+G(d,p) and CCSD(T)/6-31+G(d,p)//MPW1K/6-31+G(d,p) levels of theoretical methods qualitatively supported the B3LYP/6-31+G(d,p) results.     

Rhodium assisted CH activation of N-(2′-hydroxyphenyl)benzaldimines. Synthesis, structure and electrochemical properties of a group of organorhodium complexes

Reaction of a group of N-(2′-hydroxyphenyl)benzaldimines, derived from 2-aminophenol and five para-substituted benzaldehydes (the para substituents are OCH₃, CH₃, H, Cl and NO₂), with [Rh(PPh₃)₃Cl] in refluxing toluene in the presence of a base (NEt₃) afforded a family of organometallic complexes of rhodium(III). The crystal structure of one complex has been determined by X-ray crystallography. In these complexes the benzaldimine ligands are coordinated to the metal center, via dissociation of the phenolic proton and the phenyl proton at the ortho position of the phenyl ring in the imine fragment, as dianionic tridentate C,N,O-donors, and the two PPh₃ ligands are trans. The complexes are diamagnetic (low-spin d⁶, S = 0) and show intense MLCT transitions in the visible region. Cyclic voltammetry shows a Rh(III)Rh(IV) oxidation within 0.63-0.93 V vs SCE followed by an oxidation of the coordinated benzaldimine ligand. A reduction of the coordinated benzaldimine is also observed within −0.96 to −1.04 V vs SCE. Potential of the Rh(III)Rh(IV) oxidation is found to be sensitive to the nature of the para-substituent.     

Fluorine functionalized compounds of group 13 elements

The review gives a short survey of some developments in the synthetic chemistry of organoaluminum fluorides. Into the focus is brought the Janus-faced Lewis base-Lewis acid Al compound, group 13 difluorodiorganometalates, fluorine functionalized carbaalane derivatives, fluorination of aluminum imide clusters, diamidoaluminum fluoride, and some group 13 β-diketiminate mono- and difluorides.