https://libjncir.jncasr.ac.in/xmlui/handle/10572/1525 Sat, 04 Apr 2026 05:31:30 GMT 2026-04-04T05:31:30Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/2469 Conformational change in a urea catalyst induced by sodium cation and its effect on enantioselectivity of a Friedel-Crafts reaction Chittoory, Arjun K.; Kumari, Gayatri; Mohapatra, Sudip; Kundu, Partha P.; Maji, Tapas K.; Narayana, Chandrabhas; Rajaram, Sridhar While developing bis-camphorsulfonyl urea as a hydrogen-bonding catalysts, we discovered that the native conformation of the catalyst is unsuitable for inducing enantioselectivity. By complexing the catalyst with weakly Lewis acidic sodium cations, we were able to change the conformation of the catalyst and attain a significant improvement in the selectivity. We provide structural information from X-ray crystallography to show that the uncomplexed catalyst is indeed in an unfavorable conformation. Infrared and Raman spectroscopic studies show that sodium binds the catalyst through the carbonyl and sulfonyl groups. Simulated IR and Raman spectra match well with the experimentally recorded spectra, thereby corroborating the proposed conformational change. This result shows that weak Lewis acids can be used to tune the conformation of hydrogen-bonding catalysts and enhance the selectivity of reaction catalyzed by these systems. (C) 2014 Elsevier Ltd. All rights reserved. Restricted Access Wed, 01 Jan 2014 00:00:00 GMT https://libjncir.jncasr.ac.in/xmlui/handle/10572/2469 2014-01-01T00:00:00Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/2470 Unusual Reactivity of Nitronates with an Aryl Alkyl Carbonate: Synthesis of alpha-Amino Esters Reddy, Golipalli Ramana; Mukherjee, Debopreeti; Chittoory, Arjun Kumar; Rajaram, Sridhar The monoanions of nitroalkanes are ambident nucleophiles that react with carbonate electrophiles through the oxygen atom. Products arising from reactivity at the carbon atom will yield alpha-nitro esters, which are precursors for alpha-amino esters. We demonstrate this in the reactions of nitroalkanes with benzyl phenyl carbonate and DABCO where alpha-nitro esters are obtained instead of nitrile oxides. The products are readily reduced to alpha-amino esters. This pathway could be a safe alternative to the Strecker reaction. Restricted Access Wed, 01 Jan 2014 00:00:00 GMT https://libjncir.jncasr.ac.in/xmlui/handle/10572/2470 2014-01-01T00:00:00Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/2174 Activation of Benzyl Aryl Carbonates: The Role of Cation-pi Interactions Reddy, Golipalli Ramana; Avadhani, Anusha S.; Rajaram, Sridhar Benzyl aryl carbonates can react with a nucleophile to yield an activated electrophile and an aryloxide anion. Previously, we had utilized this in the synthesis of alpha-nitro esters from nitroalkanes. To further understand the process of activation of these carbonates by nucleophiles, we have performed kinetic studies on the hydrolysis of carbonates using nucleophiles. Rate constants for the hydrolysis were obtained under pseudo-first-order conditions with DABCO as the nucleophile. A comparison of rate constant for hydrolysis of isobutyl phenyl carbonate with benzyl phenyl carbonate shows that the presence of benzyl group results in a 16-fold acceleration of hydrolysis rate. This indicates that the transition state for activation of carbonate is stabilized by cation-pi interactions. A comparison of the rate constant for various aromatic rings indicates that electron-donating substituents on the benzyl groups accelerate the rate of hydrolysis. Studies were also carried out with DMAP as nucleophile and the results are presented. Our studies show that stable carbonates can be activated using nucleophiles. Activated acyl groups generated from acid anhydrides have been used in several enantioselective reactions. Our studies show that carbonates can be stable alternatives to acid anhydrides. Restricted Access Fri, 01 Jan 2016 00:00:00 GMT https://libjncir.jncasr.ac.in/xmlui/handle/10572/2174 2016-01-01T00:00:00Z https://libjncir.jncasr.ac.in/xmlui/handle/10572/1990 Raman, IR and DFT studies of mechanism of sodium binding to urea catalyst Kundu, Partha P.; Kumari, Gayatri; Chittoory, Arjun K.; Rajaram, Sridhar; Narayana, Chandrabhas Bis-camphorsulfonyl urea, a newly developed hydrogen bonding catalyst, was evaluated in an enantioselective Friedel Crafts reaction. We observed that complexation of the sulfonyl urea with a sodium cation enhanced the selectivity of reactions in comparison to reactions performed with urea alone. To understand the role of sodium cation, we performed Infrared and Raman spectroscopic studies. The detailed band assignment of the molecule was made by calculating spectra using Density Functional theory. Our studies suggest that the binding of the cation takes place through the oxygen atoms of carbonyl and sulfonyl groups. Natural Bond Orbital (NBO) analysis shows the expected charge distribution after sodium binding. The changes in the geometrical parameter and charge distribution are in line with the experimentally observed spectral changes. Based on these studies, we conclude that binding of the sodium cation changes the conformation of the sulfonyl urea to bring the chiral camphor groups closer to the incipient chiral center. (C) 2015 Elsevier B.V. All rights reserved. Restricted access Thu, 01 Jan 2015 00:00:00 GMT https://libjncir.jncasr.ac.in/xmlui/handle/10572/1990 2015-01-01T00:00:00Z