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.     

Order restricted inference for a multiple step-stress model with long-term survivors for a general family of distributions

In this article, we propose a failure rate based step-stress accelerated life testing (SSALT) model assuming that the time-to-event distribution belongs to a fairly general family of distributions and the underlying population consists of long term survivors. With increase in stress levels, it is expected that the mean time to the event of interest gets shortened leading to an order restriction among the mean times-to-event. We propose here a method of obtaining order restricted maximum likelihood estimators (MLEs) based on expectation maximization (EM) algorithm coupled with the method of generalized isotonic regression technique. Additionally, we address the testing of hypothesis problem for the presence of long term survivors in the underlying population based on both asymptotic and non-asymptotic approaches. To illustrate the effectiveness of the proposed method, extensive simulation experiments are carried out and a real data set is analyzed.     

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.     

A short route to the macrocyclic core of biaryl ether-based cyclopeptides

A new route based on an intramolecular Horner-Wadsworth-Emmons type olefination of amidophosphonates has been developed for the construction of a 17-membered macrocyclic scaffold related to some biologically important biaryl ether-based cyclic peptides.     

Tunneling governs intramolecular proton transfer in thiotropolone at room temperature

Successfully tunneled: The rapid and temperature-independent intramolecular proton transfer in thiotropolone occurs entirely through quantum mechanical tunneling. For tropolone, tunneling across a smaller yet broader barrier leads to a slower rate of proton transfer for temperatures smaller than 240?K.     

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.     

Lewis Acid Assisted Brønsted Acid Catalysed Decarbonylation of Isocyanates: A Combined DFT and Experimental Study

An efficient and mild reaction protocol for the decarbonylation of isocyanates has been developed using catalytic amounts of Lewis acidic boranes. The electronic nature (electron withdrawing, electron neutral, and electron donating) and the position of the substituents (ortho/meta/para) bound to isocyanate controls the chain length and composition of the products formed in the reaction. Detailed DFT studies were undertaken to account for the formation of the mono/di-carboxamidation products and benzoxazolone compounds.     

Lower Order and Higher Order Entanglement in Four‐Wave Mixing Process

Possibilities of generation of lower order and higher order intermodal entanglement in four‐wave mixing (FWM) process are rigorously investigated using Sen‐Mandal perturbative technique. The investigation has revealed that for a set of experimentally realizable parameters, one can observe lower order and higher order intermodal entanglement between pump and signal modes and signal and idler modes in a FWM process. In addition, trimodal entanglement involving pump, signal and idler modes is also reported.