Mangalampalli Ravikanth

Indian Institute of Technology Bombay, Mumbai, Mahārāshtra, India

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Publications (145)483.34 Total impact

  • A. Dvivedi, P. Rajakannu, M. Ravikanth
    Dalton Transactions 01/2015; · 4.10 Impact Factor
  • Emandi Ganapathi, Tamal Chatterjee, Mangalampalli Ravikanth
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    ABSTRACT: Expanded dithiacalixphyrins with the N2S2 core containing two sp(3) and three sp(2)meso-carbons have been prepared by condensation of one equivalent of butene-2,3-diyl-bisthiophene-2,5-diyl-bis(p-methoxyphenylmethanol) with one equivalent of 5,5'-dialkyldipyrromethane under mild acid catalyzed conditions in decent yields. The expanded dithiacalixphyrins were characterized by HR-MS, 1D and 2D NMR techniques and the structure of one of the expanded dithiacalixphyrin macrocycles was solved by X-ray crystallography. The crystal structure analysis indicated that the macrocycle is highly distorted and attains a boat shaped structure. The expanded thiacalixphyrins showed a specific sensing ability for F(-) ions over other anions as judged from absorption, NMR and mass spectral studies.
    Dalton Transactions 12/2014; · 4.10 Impact Factor
  • Sunit Kumar, Mangalampalli Ravikanth
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    ABSTRACT: A series of functionalized meso-boron dipyrromethenyl porphyrin building blocks were synthesized by condensing one equivalent of readily available 2-formyl boron dipyrromethene (2-formyl BODIPY) with two equivalents of meso-anisyl dipyrromethane and one equivalent of functionalized aldehyde under mild acid catalyzed conditions followed by column chromatographic purification and afforded in 5–7% yields. The meso-BODIPYnyl porphyrins are freely soluble in common organic solvents and characterized by mass, spectral and electrochemical techniques. The presence of a BODIPY unit directly at the meso-position alters the π-delocalization of the porphyrin macrocycle. The compounds are weakly fluorescent because of effective charge transfer between the porphyrin and BODIPY units leading to the formation of a low lying charge transfer state. The meso-BODIPYnyl porphyrin–BF2–smaragdyrin conjugate was synthesized by coupling a meso-BODIPYnyl porphyrin building block containing a meso-iodophenyl group with ethynyl BF2–smaragdyrin under Pd(0) coupling conditions. The spectral and electrochemical studies indicated that the photo-induced electron transfer is the predominant process in the meso-BODIPYnyl porphyrin–BF2–smaragdyrin conjugate.
    RSC Advances 11/2014; 4(109). · 3.71 Impact Factor
  • Tejinder Kaur, Malakalapalli Rajeswararao, Mangalampalli Ravikanth
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    ABSTRACT: We report the synthesis of first examples of hexaporphyrin and dodecaporphyrin assemblies on cyclotriphosphazene scaffold by adopting two different approaches based on Ru-pyridyl "N" coordination in decent yields. The multiporphyrin assemblies were confirmed by (31)P, (13)C, (1)H, (1)H-(1)H COSY, and NOESY NMR spectroscopic studies. The absorption studies showed 2-fold intensity enhancement with negligible changes in peak maxima compared to porphyrin monomers. The redox potentials of multiporphyrin assemblies showed the redox features of the constituted porphyrin monomers and supported weak interactions among the porphyrin units in noncovalent hexaporphyrin and dodecaporphyrin arrays.
    Inorganic Chemistry 10/2014; · 4.79 Impact Factor
  • Tamal Chatterjee, Mangalampalli Ravikanth
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    ABSTRACT: The palladium(II) complex of calixoxasmaragdyrin was prepared in 80% yield by treating the free base calixoxasmaragdyrin with PdCl2 in CH3CN at reflux temperature. The crystal structure solved for Pd(II) calixoxasmaragdyrin indicates that the calixoxasmaragdyrin macrocycle is highly distorted and attained a boat shaped structure. The Pd(II) ion is coordinated to four pyrrolic nitrogens in square planar fashion, and it is placed at ∼0.138 Å above from the four coordinating pyrrole nitrogens plane (N1N2N3N4). The Pd-N bond lengths are inequivalent, and the Pd(II) ion is positioned more toward the dipyrromethane moiety of calixoxasmaragdyrin. The complex shows one broad absorption band at 477 nm and is not very stable under redox conditions. The Pd(II) calixoxasmaragdyrin showed good catalytic activity in the Suzuki-Miyaura cross coupling reactions.
    Inorganic Chemistry 09/2014; · 4.79 Impact Factor
  • Emandi Ganapathi, Way-Zen Lee, Mangalampalli Ravikanth
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    ABSTRACT: The stable non-aromatic [20]dithiaporphyrin ( macrocycles were synthesized in decent yields by condensing readily available butene-2,3-diyl-bisthiophene-2,5-diyl-bis(p-methoxyphenylmethanol) with different meso-aryl dipyrromethanes under mild acid catalyzed conditions. The [20]dithiaporphyrin ( macrocycles are the first member of expanded porphyrin analogue of [18]dithiaporphyrin ( and consists two pyrroles and two thiophenes connected through five meso carbon bridges. The [20]dithiaporphyrin macrocycles were confirmed by mass, 1D and 2D NMR and X-ray crystallography. The X-ray structure revealed that the macrocycle is highly distorted and the two thiophene rings are completely out-of-plane from the "mean-plane" defined by the dipyrromethene moiety and the two meso carbons. In absorption spectrum, the macrocycles showed one strong band at ~420 nm and one weak band at ~720 nm. The electrochemical studies revealed that the macrocycles are stable under redox conditions. The metal sensing studies indicated that these macrocycles have potential to sense specific metal ions such as Hg2+ ion. Two covalently linked dithiahomoporphyrin-fluorophore dyads were synthesized by coupling iodo-functionalized dithiahomoporphyrin with ethynyl functionalized fluorophore such as boron-dipyrromethene (BODIPY) and BF2-smaragdyrin under mild Pd(0) coupling conditions. The potential of these dyads as fluorescent sensor for Hg2+ was explored and the studies indicated that both dyads can be used as fluorescent sensors.
    The Journal of Organic Chemistry 09/2014; · 4.64 Impact Factor
  • Emandi Ganapathi, Tamal Chatterjee, Mangalampalli Ravikanth
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    ABSTRACT: A simple route was developed for the synthesis of 9,10,19,20-tetraarylporphycenes by combining both McMurry and oxidative synthetic strategies and using readily available precursors. The desired 5,6-diaryldipyrroethenes, which were prepared in multigram quantities over two steps, were used to prepare 9,10,19,20-tetraarylporphycenes under mild acid-catalyzed conditions. As 5,6-diaryldipyrroethene precursors can easily be prepared in multigram quantities, this method is useful for the preparation of meso-tetrarylporphycenes that contain different aryl substituents. The molecular structures of these macrocycles were determined by HRMS analysis as well as 1D and 2D NMR studies. The tetraarylporphycenes exhibited a strong Soret band at approximately 380 nm and three Q bands in the region of 580–655 nm. The tetraarylprophycenes are reasonably fluorescent and stable under redox conditions.
    Annalen der Chemie und Pharmacie 09/2014; · 3.15 Impact Factor
  • Hemanta Kalita, Way-Zen Lee, Mangalampalli Ravikanth
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    ABSTRACT: The aromatic PO2 complexes of meso-triaryl-25-oxasmaragdyrins were synthesized by treating the free base 25-oxasmaragdyrins with POCl3 in toluene/triethylamine at refluxing temperature. The complexes are stable and characterized by X-ray and different spectroscopic techniques. In these complexes, the phosphorus(V) ion was bound to two pyrrolic nitrogen atoms of the smaragdyrin macrocycle and two oxygen atoms in tetrahedral geometry. The X-ray structure revealed that the smaragdyrin macrocycle showed significant distortion upon insertion of a PO2 unit, and the phosphorus atom lies 1.339 Å above the mean plane defined by three meso-carbon atoms of the macrocycle. These complexes absorb strongly in the visible region and are 2.5 times more strongly fluorescent than free base 25-oxasmaragdyrins. The smaragdyrin macrocycle becomes electron-deficient upon complexation with a PO2 unit because these complexes are easier to reduce but difficult to oxidize compared to free base smaragdyrins. We designed and synthesized a covalently linked BODIPY-PO2-smaragdyrin dyad and demonstrated efficient energy transfer from the BODIPY unit to the PO2-smaragdyrin unit.
    Inorganic Chemistry 08/2014; · 4.79 Impact Factor
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    ABSTRACT: Unsymmetrical 22‐oxacorrole containing two aryl groups and one pyrrole group at the meso position was synthesized by condensing one equivalent of 16‐oxatripyrrane with one equivalent of meso aryl dipyromethane under mild acid‐catalyzed conditions followed by oxidation with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ). This [3+2] condensation approach was expected to yield meso‐free 25‐oxasmaragdyrin but unexpectedly afforded unsymmetrical meso‐pyrrole‐substituted 22‐oxacorrole. We demonstrated the versatility of the reaction by synthesizing four new meso‐pyrrole‐substituted 22‐oxacorroles. The reactivity of α‐position of meso‐pyrrole was tested by carrying out various functionalization reactions such as bromination, formylation, and nitration and obtained the functionalized meso‐pyrrole‐substituted 22‐oxacorroles in decent yields. The X‐ray structure obtained for one of the functionalized meso‐pyrrole substituted 22‐oxacorrole revealed that the macrocycle was nearly planar and the meso‐pyrrole was in the perpendicular orientation with respect to the macrocyclic plane. The meso‐pyrrole‐substituted 22‐oxacorroles absorb strongly in 400–700 nm region with one strong Soret band and four weak Q bands. The 22‐oxacorroles are strongly fluorescent and showed emission maxima at ≈650 nm with decent quantum yields and singlet‐state lifetimes. The 22‐oxacorroles are redox‐active and exhibited three irreversible oxidations and one or two reversible reduction(s). A preliminary biological study indicated that meso‐pyrrole corroles are biocompatible. Mastering ABCorroles: Syntheses of the first examples of stable fluorescent meso‐pyrrole‐substituted 22‐oxacorroles are described (see scheme; TFA=trifluoroacetic acid; DDQ=2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone). A preliminary biological study indicated that meso‐pyrrole corroles are biocompatible.
    Chemistry 08/2014; 20(33). · 5.70 Impact Factor
  • Vellanki Lakshmi, Mangalampalli Ravikanth
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    ABSTRACT: A series of sterically crowded, mixed hexasubstituted BODIPYs containing two different types of substituents on the pyrrole carbons have been synthesized in high yields by a stepwise approach. The mixed BODIPYs were synthesized by bromination of BODIPYs followed by coupling with appropriate boronic acids under Suzuki coupling conditions. This approach has allowed the introduction of two different types of methyl/aryl substituents at the designated positions of the BODIPY core. All the hexasubstituted BODIPYs are readily soluble in common organic solvents and have been characterized by various spectral and electrochemical techniques. The spectral studies indicated that the presence of mixed methyl/aryl substituents on the BODIPY core significantly alters the electronic properties, and the electrochemical studies revealed that the BODIPYs are stable under redox conditions.
    Annalen der Chemie und Pharmacie 08/2014; · 3.15 Impact Factor
  • Yogita Pareek, M. Ravikanth
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    ABSTRACT: Review: synthesis of functionalized thiaporphyrins and their use in the construction of several covalently and non-covalently linked thiaporphyrin-based arrays; 62 refs.+ subrefs.
    ChemInform 07/2014; 45(28).
  • Sheri Madhu, Sk Josimuddin, Mangalampalli Ravikanth
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    ABSTRACT: Boron-dipyrromethenes containing dithioacetal substituents at 3,5-positions, 3,5-bis(dithioacetal) BODIPYs 1 and 2, were synthesized by treating their corresponding 3,5-diformyl BODIPYs 3 and 4 with excess methyl thioglycolate under mild acid catalyzed reaction conditions. The spectral and electrochemical studies indicated that 3,5-bis(dithioacetal) BODIPYs are less electron deficient compared to 3,5-diformyl BODIPYs. Furthermore, dithioacetal functional groups are very useful for binding metal ions and our studies clearly showed that these dyes can act as selective chemodosimetric probes for the recognition of Hg(II) ions over various other metal ions. The sensing phenomenon employs unique and irreversible Hg(II) promoted deprotection of the dithioacetal groups to aldehyde groups which is clearly demonstrated by absorption, fluorescence, HR-MS and NMR studies. Competitive binding experiments demonstrate that BODIPY 1 can specifically detect Hg(II) ions even in the presence of various other metal ions.
    New Journal of Chemistry 07/2014; 38(8). · 3.16 Impact Factor
  • Vellanki Lakshmi, Mangalampalli Ravikanth
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    ABSTRACT: Symmetrical and unsymmetrical phenylhydrazone substituted boron-dipyrromethenes were synthesized by treating 3,5-diformyl boron-dipyrromethene with phenylhydrazine/2,4-dinitrophenylhydrazine in ethanol at reflux temperature. The X-ray structure of the unsymmetrical boron-dipyrromethene (BODIPY) was shown to have an almost extended planar orientation of BODIPY with 2,4-dinitrophenylhydrozone unit at the 3-position and ethyl acetal at the 5-position with small torsional angles. A strong absorption band at 600 to 700 nm and a weak emission band at 620 to 710 nm were observed for the phenylhydrazone substituted BODIPYs. The compounds showed interesting absorption properties in DMSO and DMF solvents compared to other solvents by shifting 150 nm towards the red region. Anion binding studies indicated that the unsymmetrical phenylhydrazone substituted BODIPY could be applied as a sensor for F−, CH3COO− and H2PO4− ions as confirmed by various spectroscopic studies. Furthermore, the unsymmetrical phenylhydrazone substituted BODIPY had the unique ability of acting as a two step fluorescence enhanced chemodosimetric sensor for Fe3+ ion.
    J. Mater. Chem. C. 06/2014; 2(28).
  • Yogita Pareek, Vellanki Lakshmi, Mangalampalli Ravikanth
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    ABSTRACT: Three covalently linked dyads such as porphyrin-ferrocene, porphyrin-BODIPY and porphyrin-sapphyrin containing one hydroxyphenyl group at the meso-position of porphyrin were synthesized by coupling the trans-functionalized porphyrin building block, 5-(4-hydroxyphenyl)-10-(4-iodophenyl)-15,20-diphenyl porphyrin, with the ethynyl functionalized redox/chromophore building block under mild Pd(0) coupling conditions. The dyads were then reacted with SnTTP(OH)2 in benzene in a 2 : 1 ratio at reflux temperature for 12 hours followed by simple alumina column chromatographic purification which afforded three pentads containing three different types of redox/chromophore components in 62-80% yields. The pentads are very stable and freely soluble in all common organic solvents. The pentads formation were confirmed by MALDI-TOF mass spectrometry and 1D and 2D NMR studies. Absorption and electrochemical studies suggested that the three components in pentads retain their independent characteristic features without significant alterations in their properties thus acting like supramolecular assemblies. The steady state fluorescence studies indicated a possibility of energy/electron transfer among the three types of components in pentads.
    Dalton Transactions 03/2014; · 4.10 Impact Factor
  • Avanish Dvivedi, Yogita Pareek, Mangalampalli Ravikanth
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    ABSTRACT: A simple, one-step, supramolecular strategy was adopted to synthesize Sn(IV) -porphyrin-based axially bonded triads and higher oligomers by using meso-pyridyl Sn(IV) porphyrin, meso-hydroxyphenyl-21,23-dithiaporphyrin, and Ru(II) porphyrin as building blocks and employing complementary and non-interfering Sn(IV) O and Ru(II) ⋅⋅⋅N interactions. The multiporphyrin arrays are stable and robust and were purified by column chromatography. (1) H, (1) H-(1) H COSY and NOESY NMR spectroscopic studies were used to unequivocally deduce the molecular structures of Sn(IV) -porphyrin-based triads and higher oligomers. Absorption and electrochemical studies indicated weak interaction among the different porphyrin units in triads and higher oligomers, in support of the supramolecular nature of the arrays. Steady-state fluorescence studies on triads indicated the possibility of energy transfer in the singlet state from the basal Sn(IV) porphyrin to the axial 21,23-dithiaporphyrin. However, the higher oligomers were weakly fluorescent due to the presence of heavy Ru(II) porphyrin unit(s), which quench the fluorescence of the Sn(IV) porphyrin and 21,23-dithiaporphyrin units.
    Chemistry - A European Journal 03/2014; · 5.93 Impact Factor
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    ABSTRACT: New multiple photosynthetic reaction centers were constructed from cyclophosphazene decorated multiporphyrin chromophores and a fulleropyrrolidine having a pyridine ligand (). The excited state electron transfer in the self-assembled donor-acceptor assembly was investigated by using steady state absorption and emission, time-resolved emission spectroscopy and nanosecond laser flash photolysis. The effect of metal (Zn(2+)) coordination to porphyrin units in the multiporphyrin arrays on cyclophosphazine scaffold () was studied by comparing with metal free porphyrin assembly on a cyclophosphazene scaffold (). In , the decrease of absorption and fluorescence intensity and the lowering of the amplitude of longer fluorescence lifetime with increase of concentration reflect the formation of a ground state complex with an association constant of ∼14 910 M(-1). When compared to the metal-free complex , the metal-coordinated derivative exhibited shortening of the singlet and triplet state lifetimes and lowering of the singlet and triplet quantum yields. The cause of the decrease of the triplet quantum yields by insertion of zinc metal is discussed along with the possible non-planarity of the porphyrin ring. From the fluorescence lifetime measurements for the mixture, it is proposed that self-assembly of the donor-acceptor complex leads to charge separated species with a rate constant of 7.1 × 10(9) s(-1). The decrease of triplet state intensity and lifetime of the in the complex from the nanosecond transient absorption studies support the occurrence of intermolecular electron transfer in the triplet state.
    Physical Chemistry Chemical Physics 03/2014; · 4.20 Impact Factor
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    ABSTRACT: We report the synthesis of 3-amino boron-dipyrromethene (3-amino BODIPY) by treating 3-bromo boron-dipyrromethene (3-bromo BODIPY) initially with sodium azide in acetonitrile followed by triphenylphosphine(PPh3)/H2O in tetrahydrofuran in three steps under mild reaction conditions. In this reaction, 3-azido BODIPY which formed in the first step was not isolated but the 3-iminophosphorane BODIPY which formed in the second step was isolated and characterized crystallographically. The 3-amino BODIPY was characterized by various spectroscopic and X-ray analytical techniques. To test the reactivity of amine functionality on BODIPY core, we prepared 1-(meso-anisyl BODIPY)-3-phenyl urea/thiourea derivatives under simple reaction conditions. Our studies indicated that 1-(meso-anisyl BODIPY)-3-pheny thiourea can act as specific chemodosimetric sensor for Hg2+ ion and 1-(meso-anisyl BODIPY)-3-phenyl urea as colorimetric and ratiometric sensor for F− ion.
    Dyes and Pigments 03/2014; 102:218–227. · 3.47 Impact Factor
  • Tejinder Kaur, Way‐Zen Lee, Mangalampalli Ravikanth
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    ABSTRACT: We synthesized five N-methyl-meso-tetraaryl-21-thiaporphyrins in 55–60 % yield by treating the appropriate meso-tetraaryl-21-thiaporphyrin with CH3I. The N-methyl-21-thiaporphyrins were characterized by HRMS, 1D and 2D NMR spectroscopy, absorption spectroscopy, fluorescence spectroscopy, and electrochemical techniques, and the structure of one of the compounds was obtained by X-ray crystallography. 1D and 2D NMR spectroscopy were used to identify all of the resonances observed in the 1H NMR spectra of the N-methyl-21-thiaporphyrins. NMR studies indicated that the methylation occurred at the pyrrole ring that is opposite to the thiophene ring. In the 1H NMR spectra, the methylation resulted in significant upfield shifts of the pyrrole and thiophene protons; the maximum shifts were noted for the protons of the N-methylated pyrrole ring of the N-methyl-21-thiaporphyrins. The X-ray structure of one of the N-methyl-21-thiaporphyrins revealed significant deviation of the N-methylated pyrrole ring from the reference plane defined by the four meso carbon atoms, and the porphyrin ring is strongly distorted compared to the 21-thiaporphyrin ring. The absorption studies revealed that the N-methyl-21-thiaporphyrins showed four Q bands and one strong Soret band, which were bathochromically shifted compared to those of the 21-thiaporphyrins. The electrochemical studies on the N-methyl-21-thiaporphyrins indicated that the oxidation potentials became less positive and there were negligible shifts in the reduction potentials; the HOMO–LUMO energy gap decreased compared with that of the 21-thiaporphyrins. The N-methyl-21-thiaporphyrins are weakly fluorescent with low quantum yields and singlet-state lifetimes. The spectral and electrochemical studies indicated that N-methylation of the pyrrole ring of 21-thiaporphyrins significantly alters the electronic properties of the 21-thiaporphyrin macrocycle.
    Annalen der Chemie und Pharmacie 02/2014; · 3.15 Impact Factor
  • Tejinder Kaur, Avijit Ghosh, Palanisamy Rajakannu, Mangalampalli Ravikanth
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    ABSTRACT: The hexacoordinated rhenium(I) complex of 5,10,15,20-tetra-p-tolyl-21,23-dithiaporphyrin was synthesized, and the crystal structure analysis revealed the unusual binding mode of rhenium(I) to two thiophene sulfur atoms and one of the pyrrole nitrogen atoms of the porphyrin macrocycle.
    Inorganic Chemistry 02/2014; · 4.79 Impact Factor
  • Emandi Ganapathi, Way‐Zen Lee, Mangalampalli Ravikanth
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    ABSTRACT: An alternate synthetic route was developed for tetraaryl 27-thiasapphyrins by condensation of meso-aryl dipyrromethanes with 2,5-bis(p-tolylhydroxymethyl)thiophene under acid-catalyzed conditions. Previously, 27-thiasapphyrins have been prepared by a multistep synthesis using 2,2′-bipyrrole as the key precursor. In our strategy, the pyrrole–pyrrole bond was generated to form 27-thiasapphyrins by oxidative coupling of meso-aryl dipyrromethane and 2,5-bis(p-tolylhydroxymethyl)thiophene, and the desired 27-thiasapphyrins were isolated in 8–12 % yields. The crystal structure of one of the 27-thiasapphyrins indicates that the macrocycle is almost planar and the thiophene sulfur atom is in the plane whereas the four pyrrole nitrogen atoms slightly deviate from the plane defined by four meso carbon atoms. Absorption spectroscopy showed four well defined Q bands in 590–770 nm and one strong Soret band in 470–480 nm region for 27-thiasapphyrins. The 27-thiasapphyrins are stable under redox conditions and undergo two-to-three reversible oxidations and one-to-two reversible reductions. The macrocycles are weakly fluorescent with low quantum yields and singlet state lifetimes.
    Asian Journal of Organic Chemistry. 02/2014;