Letters in Organic Chemistry - Volume 12, Issue 5, 2015

An efficient and mild method for thioacetalization of 2-alkynylbenzaldehydes in the presence of a catalytic amount of silver triflate has been described. This reaction proceeded efficiently to generate 2-alkynylbenzaldehydes thioacetals in good to excellent yields at room temperature within short reaction time (no more than 30 min). This transformation was extremely easy to perform without the need of using anhydrous solvent and inert atmosphere. Chemoselective thioacetalization of benzaldehyde in the presence of acetophenone was also demonstrated.

During process development of Trifloxystrobin and Kresoxim-methyl fungicides, two impurities were identified. These impurities were isolated and characterized using LCMS, IR, 1H NMR, 13C NMR and elemental analysis. Structures of the impurities were further unambiguously confirmed by their independent synthesis. Structure of both impurities revealed that they possess methyl (E)-methoxyiminoacetate pharmacophore, responsible for antifungal activities of strobilurins, in combination with arylmethyl (E)-methoxyiminoacetate framework.

A novel one-pot and mild synthesis of benzoimidazole derivatives through the reaction of o-Phenylenediamine with aromatic aldehydes in the presence of MnO2 nanoparticles supported on silica as oxidizing agent under grinding conditions. The significant features of the present protocol are; simplicity of procedure, high products yields, purity of products, solvent-free condition, and easily work-up procedure.

The design and synthesis of 4-(2-adamantyl)phenylalkylamines 1-4 are described and their antiproliferative activity against four different tumor cell lines is reported.

The Friedel-Crafts acetylation of 2-acetylanthracene (2-AcAN) with AcCl and AlCl3 in 1,2-C2H4Cl2 gave a mixture of 1,6-diacetylanthracene (1,6-Ac2AN) and 1,7-diacetylanthracene (1,7-Ac2AN), while the Friedel-Crafts acetylation of 2-AcAN in nitrobenzene gave 2,7-diacetylanthracene (2,7-Ac2AN). Both reactions were highly regioselective. B3LYP/6-31G(d) calculations of diacetylanthracenes, their O-protonates and their σ-complexes indicate that 1,6-Ac2AN and 1,7-Ac2AN are the kinetically controlled products, whereas, 2,7-Ac2AN is the thermodynamically controlled product.

Triethylborane (TEB) was found to be a mild, efficient, and acid catalyst in electrophilic substitution reaction of indoles with aldehydes compounds to afford the corresponding bis(indolyl)methanes. Vibrindole A (5) and bis(indolyl)methanes derivatives 16 and 18 were synthesized using this methodology. Compound 16 is an intermediary in the synthesis of the natural bisindoles arsindoline B (2) and streptindole (6). The structure of vibrindole A (5) was unequivocally confirmed by a single crystal X-ray diffraction analysis.

A series of 2,6-bis(arylethynyl)anthraquinones was prepared via double Sonogashira coupling to 2,6-diiodoanthraquinone, and characterized with regard to their optical and electronic properties. Substitution with a derivatized phenylethynyl group produced a λonset of 366 nm (Eg = 3.4 eV), but the more highly conjugated 2,6-bis(9’-anthracylethynyl)anthraquinones exhibited a λonset of approximately 540 nm (Eg = 2.3 eV). Poor solubility in the unsubstituted 9’-anthracylethynyl system hampered complete characterization or purification, but the 10’-hexanoylanthrac-9’-ylethynyl analog exhibited significantly better solubility. The preparation of several other functionalized derivatives was also explored, and key synthetic findings are reported.

Density functional theory was used to study the tautomerization of 4-bromo substituted 1Hpyrazoles in different solvents. Mechanism and transition state structures of five tautomeric reactions were detected using quadratic synchronous transit with B3LYP method. The effect of solvent was considered with PCM method. We have found that the tautomerization is done through the transferring of hydrogen atoms between two nitrogen atoms in all tautomeric reactions. Also, it was found that the tautomeric reaction rate is dependent on solvent and reach to constant value for solvents with dielectric constant of greater than 8.93. Moreover, we found that the effect of solvent on equilibrium constant is dependent on considered molecules.

2H-Chromene and its derivatives are an important class of organic compounds due to their wide range of biological activities such as antimicrobial, antiviral, antiimflamatory and antitubercular agents. In the present work we have synthesized ten new 2H-chromene derivatives [(E)-4-(2-phenyl- 2H-chromen-3-yl)but-3-en-2-one and its substituted analogues] following aldol condensation of 2Hchromene- 3-carbaldehydes with acetone. These products have been characterized by means of spectral data (1H, 13C, IR, Mass). The structure of one new compound (E)-4-(6,8-dichloro-2-phenyl-2H-chromen-3-yl)but-3-en-2- one was confirmed by X-ray analysis and the product was subsequently subjected to the in vitro evaluation of antimicrobial activity against two Gram positive bacteria Streptococcus mutans (MTCC 497) and Streptococcus pyogenes (MTCC 1926) and three Gram negative bacteria Vibrio cholera (MTCC 3909), Shigella flexneri (MTCC 1457) and Salmonella enteric typhi (MTCC 1252). The obtained results from in vitro antimicrobial assays by broth dilution method indicated that many compounds under study exhibited excellent activity against all the microorganisms in comparison to standard kanamycin.

In the presence of KF as base and THF as solvent, the tandem Michael addition-elimination reaction of different 5-alkoxy-3,4-dihalo-2(5H)-furanones with aminomethyl benzimidazoles at room temperature gave 21 target compounds simultaneously containing both bioactive benzimidazole and 2(5H)-furanone moieties in yields of 62-88 % (mostly over 71 %). The structures of all the newly synthesized compounds were elucidated and confirmed by FTIR, UV, 1H NMR, 13C NMR, mass spectroscopy and elemental analysis. The simple one-pot synthetic method provides a brief route for the introduction of the benzimidazole unit into 2(5H)-furanone derivatives under mild conditions without any metal catalysts. This transformation also affords an important synthetic strategy for the series 2(5H)-furanone derivatives, as well as a basis for the activity test of these potential drug molecules.