01208nas a2200193 4500008004100000245006200041210005600103260000800159300001600167490000700183520060300190100001700793700002300810700002200833700001800855700003100873700002200904856008800926 2017 eng d00aN - heterocyclic - carbene - catalyzed umpolung of imines0 aN heterocyclic carbene catalyzed umpolung of imines cMAR a2730 - 27340 v563 a

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.

1 aPatra, Atanu1 aMukherjee, Subrata1 aDas, Tamal, Kanti1 aJain, Shailja1 aGonnade, Rajesh, Ghanshyam1 aBiju, Akkattu, T. uhttps://library.ncl.res.in/content/n-heterocyclic-carbene-catalyzed-umpolung-imines00917nas a2200181 4500008004100000245011900041210006900160260000800229300001600237490000700253520024500260100001900505700002600524700001900550700001700569700001800586856013100604 2017 eng d00a p-Selective (sp(2))-C-H functionalization for an acylation/alkylation reaction using organic photoredox catalysis0 apSelective sp2CH functionalization for an acylationalkylation re cNOV a12337-123400 v533 ap-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.1 aPandey, Ganesh1 aTiwari, Sandip, Kumar1 aSingh, Bhawana1 aVanka, Kumar1 aJain, Shailja uhttps://library.ncl.res.in/content/p-selective-sp2-c-h-functionalization-acylationalkylation-reaction-using-organic-photoredox01698nas a2200145 4500008004100000245009400041210006900135260000800204300001600212490000700228520117100235100001801406700001701424856011101441 2017 eng d00aUnusual role of the aromatic solvent in single site Al(I) chemistry: insights from theory0 aUnusual role of the aromatic solvent in single site AlI chemistr cJUL a13957-139630 v233 aThe 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.1 aJain, Shailja1 aVanka, Kumar uhttps://library.ncl.res.in/content/unusual-role-aromatic-solvent-single-site-ali-chemistry-insights-theory02240nas a2200205 4500008004100000022001400041245009000055210006900145260000800214300001400222490000700236520155700243100002401800700001801824700002101842700002401863700001701887700002001904856011001924 2018 eng d a0276-733300aMechanism of nickel(II)-catalyzed C(2)-H alkynylation of indoles with alkynyl bromide0 aMechanism of nickelIIcatalyzed C2H alkynylation of indoles with  cJUL a2037-20450 v373 a

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'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.

1 aKhake, Shrikant, M.1 aJain, Shailja1 aPatel, Ulhas, N.1 aGonnade, Rajesh, G.1 aVanka, Kumar1 aPunji, Benudhar uhttps://library.ncl.res.in/content/mechanism-nickelii-catalyzed-c2-h-alkynylation-indoles-alkynyl-bromide02045nas a2200205 4500008004100000022001400041245010400055210006900159260000800228300001400236490000700250520133400257100002101591700001801612700002201630700002401652700001701676700002001693856012601713 2018 eng d a0276-733300aMechanistic aspects of pincer nickel(II)-catalyzed C-H bond alkylation of azoles with alkyl halides0 aMechanistic aspects of pincer nickelIIcatalyzed CH bond alkylati cMAR a1017-10250 v373 a

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.

1 aPatel, Ulhas, N.1 aJain, Shailja1 aPandey, Dilip, K.1 aGonnade, Rajesh, G.1 aVanka, Kumar1 aPunji, Benudhar uhttps://library.ncl.res.in/content/mechanistic-aspects-pincer-nickelii-catalyzed-c-h-bond-alkylation-azoles-alkyl-halides01530nas a2200157 4500008004100000022001400041245010900055210006900164260000800233300001600241490000700257520094700264100001801211700001701229856012601246 2019 eng d a1463-907600aCan the solvent enhance the rate of chemical reactions through C-H/pi interactions? insights from theory0 aCan the solvent enhance the rate of chemical reactions through C cJUL a14821-148310 v213 a

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.

1 aJain, Shailja1 aVanka, Kumar uhttps://library.ncl.res.in/content/can-solvent-enhance-rate-chemical-reactions-through-c-hpi-interactions-insights-theory01113nas a2200193 4500008004100000022001400041245012400055210006900179260000800248300001400256490000700270520042200277100001700699700002000716700001800736700001700754700002000771856012800791 2019 eng d a1477-052000aDiastereoselective multi-component tandem condensation: synthesis of 2-amino-4-(2-furanone)-4H-chromene-3-carbonitriles0 aDiastereoselective multicomponent tandem condensation synthesis  cOCT a8853-88570 v173 a

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.

1 aGupta, Vijay1 aSahu, Debashish1 aJain, Shailja1 aVanka, Kumar1 aSingh, Ravi, P. uhttps://library.ncl.res.in/content/diastereoselective-multi-component-tandem-condensation-synthesis-2-amino-4-2-furanone-4h01926nas a2200157 4500008004100000022001400041245016900055210006900224260000900293300001400302490000800316520128400324100001801608700001701626856012501643 2020 eng d a1089-563900aEffect of solvent-substrate noncovalent interactions on the diastereoselectivity in the intramolecular carbonyl-ene and the staudinger [2+2] cycloaddition reactions0 aEffect of solventsubstrate noncovalent interactions on the diast cOCT  a8019-80280 v1243 a

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.

1 aJain, Shailja1 aVanka, Kumar uhttps://library.ncl.res.in/content/effect-solvent-substrate-noncovalent-interactions-diastereoselectivity-intramolecular00974nas a2200193 4500008004100000022001400041245010700055210006900162260000900231300001600240490000700256520029500263100001700558700002400575700001800599700001700617700001900634856012700653 2021 eng d a1359-734500aDeoxygenative hydroboration of primary and secondary amides: a catalyst-free and solvent-free approach0 aDeoxygenative hydroboration of primary and secondary amides a ca cOCT  a10596-105990 v573 aIn 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.1 aKumar, Rohit1 aBisai, Milan, Kumar1 aJain, Shailja1 aVanka, Kumar1 aSen, Sakya, S. uhttps://library.ncl.res.in/content/deoxygenative-hydroboration-primary-and-secondary-amides-catalyst-free-and-solvent-free01579nas a2200205 4500008004100000022001400041245014300055210007100198260000800269300001200277490000600289520081600295100002401111700002201135700001801157700002601175700001701201700002201218856013301240 2022 eng d a2052-412900aSilver-catalyzed [3 + 3]-annulation cascade of alkynyl alcohols and α,β-unsaturated ketones for the regioselective assembly of chromanes0 aSilvercatalyzed 3 3annulation cascade of alkynyl alcohols and αβ cJAN a802-8090 v93 aAn 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–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.1 aNakate, Ashwini, K.1 aThorat, Sagar, S.1 aJain, Shailja1 aKrishna, Gamidi, Rama1 aVanka, Kumar1 aKontham, Ravindar uhttps://library.ncl.res.in/content/silver-catalyzed-3-3-annulation-cascade-alkynyl-alcohols-and-%CE%B1%CE%B2-unsaturated-ketones01265nas a2200253 4500008004100000022001400041245010900055210006900164260000900233300001500242490000700257520044600264653001200710653002300722653001800745653002400763100001700787700001900804700001800823700002100841700001700862700001900879856011300898 2022 eng d a1867-388000aWell-defined calcium compound catalyzes trimerization of arylisocyanates into 1,3,5-triarylisocyanurates0 aWelldefined calcium compound catalyzes trimerization of arylisoc cJUN  ae2021017880 v143 a

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.

10acalcium10aCyclotrimerization10aIsocyanurates10aTetradentate ligand1 aKumar, Rohit1 aSharma, Vishal1 aJain, Shailja1 aSharma, Himanshu1 aVanka, Kumar1 aSen, Sakya, S. uhttps://library.ncl.res.in/content/well-defined-calcium-compound-catalyzes-trimerization-arylisocyanates-135