Apical Functionalization of Tribenzotriquinacenes

The introduction of one alkyne moiety at the central carbon atom of the tripodal tribenzotriquinacene scaffold allows easy access to a great variety of apically functionalized derivatives. The spatially well‐separated arrangement of different functional units on the convex face and outer rim was further proven by single‐crystal X‐ray studies. Subsequent modifications that feature a general protecting group‐free strategy for the demethylation of protected catechols in the presence of a terminal alkyne group, an azide–alkyne Huisgen cycloaddition, and Sonogashira cross‐coupling reactions showcase the high synthetic potential of this modular approach for tribenzotriquinacene derivatization.     

Rapid and Sensitive LC Method for the Analysis of Gemifloxacin in Human Plasma

A simple liquid chromatographic method for the determination of gemifloxacin (CAS number 175463-14-6) in human plasma has been developed. An aliquot quantity of 1 mL plasma sample was taken and 0.1 mL internal standard was added and mixed. 1 mL methanol was added to it. The mixture was then sonicated for 10 min followed by 20 min centrifugation at 5000 rpm (g = 3600). The supernatant layer was separated and filtered through simple filtration unit (membrane filter, 0.45 μm) and injected into the LC system consisting of Hypersil BDS, C18 (250 × 4.6 mm, 5 μm particle size) column, using 1% formic acid : methanol = 65:35 (v/v) as mobile phase with ultra violet detection at 328 nm. Lower limit of detection was 20 ng mL^?1 and lower limit of quantitation was 50 ng mL^?1. Maximum between-run precision was 14.614%. Mean extraction recovery was found to be 87.32 to 89.32%. Stability study showed that after three freeze-thaw cycles the loss of three quality control samples were less than 10%. Samples were stable at room temperature for 12 h and at ?20 °C for 3 months. Before injecting into LC system, the processed samples were stable for at least 8 h. The method was used to perform bioequivalence study in human volunteers.     

Triarylborane‐Catalyzed Alkenylation Reactions of Aryl Esters with Diazo Compounds

Herein we report a facile, mild reaction protocol to form carbon–carbon bonds in the absence of transition metal catalysts. We demonstrate the metal‐free alkenylation reactions of aryl esters with α‐diazoesters to give highly functionalized enyne products. Catalytic amounts of tris(pentafluorophenyl)borane (10–20 mol %) are employed to afford the C=C coupled products (31 examples) in good to excellent yields (36–87 %). DFT studies were used to elucidate the mechanism for this alkenylation reaction.     

Color Polymorphism: Understanding the Diverse Solid‐State Packing and Color in Dimethyl‐3,6‐dichloro‐2,5‐dihydroxyterephthalate

Dimethyl‐3,6‐dichloro‐2,5‐dihydroxyterephthalate (MCHT) is known to exist in three differently packed crystals having three different colors, namely yellow (Y), light yellow (LY), and white (W). Apart from the difference in their color, the molecules in the crystals also differ in their intramolecular O?H???O and O?H???Cl hydrogen bonds. Time‐dependent DFT calculations reveal the role of the various types of hydrogen bonds in controlling the color of the polymorphs. Mechanistic pathways that lead to such transformations in the crystal are elucidated by solid‐state dispersion‐corrected DFT studies. Relative stabilities of the various polymorphs rationalize the experimentally observed transformations between them. Calculations reveal that the minimum‐energy pathway for the conversion of the Y form to a W form is through stepwise disrotatory motion of the two ?OH groups through a hybrid intermediate having one intramolecular O?H???O and one O?H???Cl bond. The LY form is shown to exist on the higher‐energy pathway involving a concerted Y→W transformation.