@article {43352, title = {N - heterocyclic - carbene - catalyzed umpolung of imines}, journal = {Angewandte Chemie International Edition}, volume = {56}, year = {2017}, month = {MAR}, pages = {2730 - 2734}, type = {Article}, abstract = {

N-Heterocyclic carbene (NHC) catalysis has been widely used for the umpolung of aldehydes, and recently for the umpolung of Michael acceptors. Described herein is the umpolung of aldimines catalyzed by NHCs, and the reaction likely proceeds via aza-Breslow intermediates. The NHC-catalyzed intramolecular cyclization of aldimines bearing a Michael acceptor resulted in the formation of biologically important 2-(hetero)aryl indole 3-acetic-acid derivatives in moderate to good yields. The carbene generated from the bicyclic triazolium salt was found to be efficient for this transformation.

}, doi = {10.1002/anie.201611268}, author = {Patra, Atanu and Mukherjee, Subrata and Das, Tamal Kanti and Jain, Shailja and Gonnade, Rajesh Ghanshyam and Biju, Akkattu T.} } @article {44124, title = { p-Selective (sp(2))-C-H functionalization for an acylation/alkylation reaction using organic photoredox catalysis}, journal = { Chemical Communications}, volume = {53}, year = {2017}, month = {NOV}, pages = {12337-12340}, type = {Article}, abstract = {p-Selective (sp(2))-C-H functionalization of electron rich arenes has been achieved for acylation and alkylation reactions, respectively, with acyl/alkylselenides by organic photoredox catalysis involving an interesting mechanistic pathway.}, doi = {10.1039/c7cc07529d}, author = {Pandey, Ganesh and Tiwari, Sandip Kumar and Singh, Bhawana and Vanka, Kumar and Jain, Shailja} } @article {43984, title = {Unusual role of the aromatic solvent in single site Al(I) chemistry: insights from theory}, journal = {Chemistry - A European Journal}, volume = {23}, year = {2017}, month = {JUL}, pages = {13957-13963}, type = {Article}, abstract = {The single site activation of strong σ bonds (such as that of H-H, P-H and N-H) remains a significant challenge in main group chemistry, with only a few cases reported to date. In this regard, recent exciting experiments done with Al(I) complexes hold significance, because they, too, have been seen to activate a variety of strong σ bonds. Such chemistry is generally seen to occur in aromatic solvents. The current computational studies with density functional theory (DFT) reveal the interesting reason for this: it is seen that an explicit aromatic solvent molecule acts as a catalyst by converting the Al(I) complex to Al(III) during the process. Different cases of σ bond activation by Al(I) complexes have been investigated and the efficiency for the H-X (X=H, NHtBu, PPh2) bond activation in the presence of an explicit benzene solvent molecule has been seen to be orders of magnitude higher than in its absence. The current work therefore reveals the chemistry of Al(I) complexes to be richer and more complex than realized to date, and shows it to be dependent on metal-solvent cooperativity, the first known example of its kind in main group chemistry.}, doi = {10.1002/chem.201701642}, author = {Jain, Shailja and Vanka, Kumar} } @article {44620, title = {Mechanism of nickel(II)-catalyzed C(2)-H alkynylation of indoles with alkynyl bromide}, journal = {Organometallics}, volume = {37}, year = {2018}, month = {JUL}, pages = {2037-2045}, abstract = {

The nickel system (THF)(2)NiBr2/phen has recently been shown as an efficient catalyst for the C-H bond alkynylation of diverse heteroarenes with (triisopropylsilyl)alkynyl bromide via monodentate chelation assistance. Herein, we report an extensive mechanistic investigation for the direct alkynylation of indoles involving the well-defined nickel catalyst, which features a coordinative insertion pathway of alkynyl bromide with the Ni(II) catalyst. Catalytic relevant nickel complexes, (phen)NiCl2 (5), (phen)(2)NiCl2 (6) and [(phen)(3)Ni].NiCl4 (7) were isolated, and the complexes 6 and 7 were structurally characterized. Well-defined complexes were as competent as the in situ generated catalyst system (THF)(2)NiBr2/phen for the alkynylation of indoles. Various controlled studies and reactivity experiments were performed to understand the probable pathway for the alkynylation reaction. Kinetics analysis highlights that the complex (phen)NiX2 acts as a precatalyst, and the involvement of substrate indole and LiO{\textquoteright}Bu are essential for the generation of the active catalyst. Deuterium labeling and kinetic studies suggest that the process involving C-H cleavage and carbo-nickelation of indole is a crucial rate influencing step. Reactivity study of various alkynyl compounds with nickel-species highlights a migratory insertion route for the reaction. DFT calculations firmly support the experimental findings and suggest the coordinative insertion pathway of alkynyl bromide rather than oxidative addition toward the nickel(II) center.

}, issn = {0276-7333}, doi = {10.1021/acs.organomet.8b00177}, author = {Khake, Shrikant M. and Jain, Shailja and Patel, Ulhas N. and Gonnade, Rajesh G. and Vanka, Kumar and Punji, Benudhar} } @article {44517, title = {Mechanistic aspects of pincer nickel(II)-catalyzed C-H bond alkylation of azoles with alkyl halides}, journal = {Organometallics}, volume = {37}, year = {2018}, month = {MAR}, pages = {1017-1025}, abstract = {

The quinolinyl-based pincer nickel complex, kappa(N),kappa(N),kappa(N)-{C9H6N-(mu-N)-C6H4-NMe2}NiCl [((NNNMe2)-N-Q)-NiCl; (1)] has recently been demonstrated to be an efficient and robust catalyst for the alkylation of azoles with alkyl halides under copper-free conditions. Herein, we report the detailed mechanistic investigation for the alkylation of azoles catalyzed by ((NNNMe2)-N-Q)NiCl (1), which highlights an iodine atom transfer (IAT) mechanism for the reaction involving a Ni-II/Ni-III process. Deuterium labeling experiments indicate reversible cleavage of the benzothiazole C-H bond, and kinetic studies underline a fractional negative rate order with the substrate benzothiazole. The involvement of an alkyl radical during the alkylation is validated by radical clock and external additive experiments. An active intermediate species ((NNNMe2)-N-Q)Ni(benzothiazolyl) (5a) has been isolated and structurally characterized. The complex ((NNNMe2)-N-Q)Ni(benzothiazoly1) (5a) is found to be the resting state of catalyst 1. Kinetic analysis of electronically different intermediates suggests that the step involving the reaction of 5a with alkyl iodide is crucial and a rate-influencing step. DFT calculations strongly support the experimental findings and corroborate an IAT process for the alkylation reaction.

}, issn = {0276-7333}, doi = {10.1021/acs.organomet.8b00025}, author = {Patel, Ulhas N. and Jain, Shailja and Pandey, Dilip K. and Gonnade, Rajesh G. and Vanka, Kumar and Punji, Benudhar} } @article {46295, title = {Can the solvent enhance the rate of chemical reactions through C-H/pi interactions? insights from theory}, journal = {Physical Chemistry Chemical Physics}, volume = {21}, year = {2019}, month = {JUL}, pages = {14821-14831}, type = {Article}, abstract = {

The current computational study with density functional theory (DFT) shows that the rate of chemical reactions can be influenced through non-covalent C-H/p interactions between substrates and the solvent. It is shown that intramolecular carbon-carbon interaction and CO2 activation by a low valent silicon complex are both favourably affected by the explicit presence of the solvent toluene, due to C-H/p interactions between toluene and the silicon complex. Furthermore, ab initio molecular dynamics (AIMD) simulations demonstrate that even if the C-H/p interacting solvent molecule is displaced from the complex, another would quickly take its place, thus maintaining the interaction. Hence, the current work shows how non-covalent interactions between solvent and substrate can enhance the rate of the reaction and expands our understanding of the role and influence of the solvent in effecting important chemical transformations.

}, issn = {1463-9076}, doi = {10.1039/c9cp02646k}, author = {Jain, Shailja and Vanka, Kumar} } @article {46322, title = {Diastereoselective multi-component tandem condensation: synthesis of 2-amino-4-(2-furanone)-4H-chromene-3-carbonitriles}, journal = {Organic \& Biomolecular Chemistry}, volume = {17}, year = {2019}, month = {OCT}, pages = {8853-8857}, type = {Article}, abstract = {

A general strategy for a one-pot stereoselective synthesis of 2-amino-4-(2-furanone)-4H-chromene-3-carbonitriles by reaction of salicylaldehyde, malononitrile and butenolides via a tandem Knoevenagel/Pinner/vinylogous Michael condensation is presented. The beta,gamma-butenolides gave a syn-selective MCR adduct with a dr up to 11.5 : 1. The mechanistic insight into the MCR was obtained by DFT calculations.

}, issn = {1477-0520}, doi = {10.1039/c9ob01345h}, author = {Gupta, Vijay and Sahu, Debashish and Jain, Shailja and Vanka, Kumar and Singh, Ravi P.} } @article {46690, title = {Effect of solvent-substrate noncovalent interactions on the diastereoselectivity in the intramolecular carbonyl-ene and the staudinger [2+2] cycloaddition reactions}, journal = {Journal of Physical Chemistry A}, volume = {124}, year = {2020}, month = {OCT }, pages = {8019-8028}, type = {Article}, abstract = {

Noncovalent interactions (NCIs) have been identified as important contributing factors for determining selectivity in organic transformations. However, cases where NCIs between solvents and substrates are responsible for a major extent for determining selectivity are rare. The current computational study with density functional theory identifies two important transformations where this is the case: the intramolecular carbonyl-ene reaction and the Staudinger [2 + 2] cycloaddition reaction. In both cases, the role of explicit solvent molecules interacting non-covalently with the substrate has been taken into account. Calculations indicate that the diastereomeric ratio would be 95.0:5.0 for the formation of tricyclic tetrahydrofuran diastereomers via the intramolecular carbonyl-ene reaction and 94.0:6.0 for the formation of the triflone diastereomers via the Staudinger [2 + 2] cycloaddition reaction, which corroborates with the experiment. Interestingly, in both the cases, the calculations indicate that noninclusion of explicit solvent molecules would lead to only a small difference between the competing transition states, which leads to the conclusion that solvent-substrate NCIs are the major cause for diastereoselectivity in both the cases considered.

}, issn = {1089-5639}, doi = {10.1021/acs.jpca.0c05738}, author = {Jain, Shailja and Vanka, Kumar} } @article {47644, title = {Deoxygenative hydroboration of primary and secondary amides: a catalyst-free and solvent-free approach}, journal = {Chemical Communications}, volume = {57}, year = {2021}, month = {OCT }, pages = {10596-10599}, type = {Article}, abstract = {In contrast to the recent reports on catalytic hydroboration of amides to amines with pinacolborane (HBpin), a simple catalyst-free and solvent-free method for the hydroboration of a variety of amides has been realized. To get the mechanistic insights, DFT calculations have been performed.}, issn = {1359-7345}, doi = {10.1039/d1cc04148g}, author = {Kumar, Rohit and Bisai, Milan Kumar and Jain, Shailja and Vanka, Kumar and Sen, Sakya S.} } @article {47834, title = {Silver-catalyzed [3 + 3]-annulation cascade of alkynyl alcohols and α,β-unsaturated ketones for the regioselective assembly of chromanes}, journal = {Organic Chemistry Frontiers}, volume = {9}, year = {2022}, month = {JAN}, pages = {802-809}, type = {Article}, abstract = {An unprecedented Ag(i)-catalyzed [3 + 3]-annulation of alkynyl alcohols (5-hexyn-1-ols) and α,β-unsaturated ketones is reported to construct simple to complex chromanes. This transformation begins with hydroalkoxylation of alkynol through C{\textendash}C triple bond activation to give cyclic-enol ether, followed by intermolecular 1,4-addition and intramolecular 1,2-addition of enol ethers onto the enone and oxidative aromatization or Grob-type elimination steps. Facile reaction conditions, broad substrate scope, good to excellent yields, and atom economy are the salient features of this protocol. Isolation of the active pyran-tethered cyclohexadiene reaction intermediate, additional supporting experiments, and DFT calculations strongly support the experimental findings and corroborate our proposed mechanism.}, issn = {2052-4129}, doi = {10.1039/D1QO01643A}, author = {Nakate, Ashwini K. and Thorat, Sagar S. and Jain, Shailja and Rama Krishna, Gamidi and Vanka, Kumar and Kontham, Ravindar} } @article {48032, title = {Well-defined calcium compound catalyzes trimerization of arylisocyanates into 1,3,5-triarylisocyanurates}, journal = {ChemCatChem}, volume = {14}, year = {2022}, month = {JUN }, pages = {e202101788}, type = {Article}, abstract = {

We report the synthesis of a calcium complex (2) bearing a tetradentate monoanionic ligand with a diaminoethane core and phenolate and pyridine peripheral donors. Single crystal X-ray studies on 2 revealed that LiI was also co-crystallized, leading to a four-membered ring with four different elements. 2 was found to be an efficient catalyst for the cyclotrimerization of a variety of aromatic isocyanates under mild conditions.

}, keywords = {calcium, Cyclotrimerization, Isocyanurates, Tetradentate ligand}, issn = {1867-3880}, doi = {10.1002/cctc.202101788}, author = {Kumar, Rohit and Sharma, Vishal and Jain, Shailja and Sharma, Himanshu and Vanka, Kumar and Sen, Sakya S.} }