Ch. Sanjeeva Reddy

ZrCl4-catalyzed Pechmann reaction : Synthesis of coumarins under solvent-free conditions

Abstract Zirconium (IV) chloride is used as an efficient catalyst in the Pechmann condensation reaction of phenols with β‐keto esters leading to the formation of coumarin derivatives in good yields under solvent‐free conditions.

ZrCl4 as a mild and efficient catalyst for the one-pot conversion of TBS and THP ethers to acetates

Abstract A mild, efficient and chemoselective method has been developed for the direct transformation of tert -butyldimethylsilyl and tetrahydropyranyl protected alcohols into the corresponding acetates with acetic anhydride and zirconium(IV) chloride as the catalyst in acetonitrile, in a one-pot reaction with high yields and short reaction times. This method has been applied to a variety of substrates.

A one-pot azido reductive tandem mono-N-alkylation employing dialkylboron triflates: online ESI-MS mechanistic investigation.

An efficient one-pot reductive tandem mono-N-alkylation of both aromatic and aliphatic azides using dialkylboron triflates as alkylating agents has been examined under standardized reaction conditions. This methodology after optimization has been employed toward the syntheses of various secondary alkyl as well as aryl amines, including the synthesis of N10-butylated pyrrolo[2,1-c][1,4]benzodiazepine-5,11-diones via in situ azido reductive-cyclization process. This protocol is particularly attractive to provide an environmentally benign and practical method for mono-N-alkylation from organic azides without the use of toxic catalysts or corrosive alkylating agents. In addition, the mechanistic aspects have been investigated and the intermediates associated with this selective transformation have been intercepted and characterized by online monitoring of the reaction by ESI-MS/MS.

Mechanism of acid bromate oxidation of trans mono-substituted cinnamic acids: structure reactivity correlation - a non-linear hammett's plot

Abstract Oxidation of cinnamic and trans mono-substituted cinnamic acids with Br(V), unmixed by generated molecular bromine addition, has been studied from the kinetic and mechanistic aspects. Acid bromate, in the presence of mercury(II), oxidises cinnamic acids smoothly and quantitatively to the respective benzaldehydes. Reactions are catalysed by mineral acids and they exhibit first, fractional orders in [Br(V)] and [substrate] respectively. An inverse secondary deuterium kinetic isotope effect characterises the oxidation and reaction rates increase when deuterium replaces either α or β-proton of cinnamic acids. Oxidation rate is not much affected by electron attractors whereas it is susceptible to electron demand at the seat of the reaction. The free energy relationship is characterised by two distinct lines in the Hammetts plot with ϱ values of -3.7 and -0.8 for the two limbs. Two alternative mechanistic pathways have been proposed involving (i) a partially and a fully developed benzylic carbonium ion like activated complex for electron attractors and donors respectively in the slow and the rate determining step, or (ii) two discrete centres viz. Cα and Cβ passing via C+α and C+β carbonium ion intermediate for electron attractors and donors respectively. Mercury(II) role is only in scavenging bromide ions.

Oxidative kinetics of aminoacids by N-bromoacetamide. A study of solvent effect and general base catalysis

Abstract The kinetic results of the oxidation of aminoacids by N-bromoacetamide in acid and alkaline media are presented. It is noticed that the order with respect to substrate is dependent on the nature of the medium, 0.30 – 0.80 in perchloric acid (except phenylalanine in which case the order is 1.0) and alkaline media and zero order in aqueous acetic acid. Irrespective of the medium, the reaction is first order in [oxidant]. The rate of oxidation increases with [OH - ] and decreases with [H + ]. The changes observed in the direction of the pH-rate profile correspond to the ionization constants of the aminoacids. The reaction is inhibited by the addition of acetamide in perchloric acid medium but, is independent of it in alkaline medium. The rate of oxidation is susceptible to changes in the composition of acetic acid and is maximum at 25% aqueous acetic acid. The oxidation of aminoacids by N-bromoacetamide is also catalysed by carboxylate anions. The catalytic constants of propionate, butyrate, acetate, chloropropionate and chloroacetate are measured and Bronsted coefficients (β) so evaluated are in the range 0.38 – 0.46. The proposed mechanism and the derived rate laws are consistent with the observed kinetics.

Facile and regioselective conversion of epoxides into β-chlorohydrins using ZrCl4

Epoxides were efficiently converted into the corresponding β-chlorohydrins in good yields by treatment with ZrCl4 in acetonitrile.

Synthesis, characterization and molecular docking studies of novel 2-amino 3-cyano pyrano[2,3H]chrysin derivatives as potential antimicrobial agents

AbstractA series of novel 2-amino 3-cyano 4-aryl pyrano[2,3H]chrysin derivatives (3a–m) were efficiently synthesized by one-pot three-component reaction of aromatic aldehydes, malononitrile and chrysin and characterized by 1H NMR, 13C NMR and mass spectral data. All the newly synthesized compounds were evaluated for their in vitro antimicrobial activity (antibacterial and antifungal). Among the tested compounds, 3a, 3g, 3h, 3j and 3k showed potent antibacterial activity compared to ciprofloxacin and the compounds 3a, 3g, 3h, 3i and 3k showed excellent antifungal activity compared to itrazole. The compounds 3a, 3g, 3h and 3k exhibited potent antimicrobial activity against all the selected pathogenic bacteria and fungi and emerged as potential molecules for further development. In addition, molecular modeling studies also performed to delineate the putative binding mode of these compounds. All of these chrysin derivatives (3a–m) obeyed the Lipinski’s “rule of five” and have drug-likeness. Docking scores with appreciable binding energy values also exactly correlated with the experimental antimicrobial activity. The chemscore estimated by GOLD software was found to have a good correlation with the experimental inhibitory activity.Graphical AbstractDocking of compound 3g with protein A series of novel 2-amino 3-cyano pyrano[2,3H]chrysin derivatives (3a–m) has been synthesized and evaluated for their antimicrobial activity along with molecular modeling studies

Cerium(III) ion catalysis in the oxalic acid-bromate reaction: Anomalous kinetic behavior of oxalic acid

The kinetics of cerium(III) ion catalyzed Br(V) oxidation of oxalic acid in the presence of HClO4/H2SO4 and mercury(II)-a bromide removing ion, exhibits second order each in [br(V)] and [acid], 0.4 and zero order in [Ce(III)]. However, the kinetic behavior of oxalic acid is anomalous with −0.7, zero and 1.4 order. The chemistry underlying the phenomena is discussed.AbstractКинетика окисления щавелевой кислоты ионом Br(V), катализированного ионом Ce(III), в присутствии HClO4/H2SO4 и ртути (II), удаляющеи ион бромида, свидетельствует о втором порядке реакции как по [Br(V)], так и по [кислоты], 0,4 и нулевого порядка по [Ce(III)]. Однако, кинетическое поведение щвелевой кислоты аномально, т.к. порядок реакции ио ней равен −0,7, 0 и 1,4. Обсуждается химия, лежащая в основе зтнх явлений.