@article { ISI:000338023000039, title = {Direct allylation of in situ generated aldehyde acyl anions by synergistic NHC and palladium catalysis}, journal = {Angewandte Chemie-International Edition}, volume = {53}, number = {27}, year = {2014}, month = {JUL}, pages = {7038-7042}, publisher = {WILEY-V C H VERLAG GMBH}, type = {Article}, address = {BOSCHSTRASSE 12, D-69469 WEINHEIM, GERMANY}, abstract = {

The direct regioselective allylation of in situ generated aldehyde acyl anions has been achieved by synergistic NHC and Pd catalysis. It provides an efficient access to valuable beta,gamma-unsaturated ketones under mild reaction conditions starting from easily accessible allylic carbonates and aldehydes without any preactivation. The synergistic catalysis method demonstrated herein adds a new dimension to the area of metal-mediated C allylation.

}, keywords = {aldehyde umpolung, C allylation, N-heterocyclic carbenes, Palladium, synergistic catalysis}, issn = {1433-7851}, doi = {10.1002/anie.201400623}, author = {Ahire, Milind M. and Mhaske, Santosh B.} } @article { ISI:000367722500058, title = {N-Heterocyclic carbene catalyzed oxidative coupling of alkenes/alpha-bromoacetophenones with aldehydes: a facile entry to alpha,beta-epoxy ketones}, journal = {Angewandte Chemie-International Edition}, volume = {54}, number = {47}, year = {2015}, month = {NOV}, pages = {14150-14153}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {

{A novel, N-heterocyclic carbene (NHC) catalyzed direct oxidative coupling of styrenes with aldehydes has been described for the synthesis of alpha,beta-epoxy ketones in good yields. This unprecedented regioselective oxidative coupling employs NBS/DBU/DMSO (DBU = 1,8-diazabicyclo [5.4. 0] undec-7-ene

}, keywords = {aldehydes, epoxidation, N-heterocyclic carbenes, Oxidation, synthetic methods}, issn = {1433-7851}, doi = {10.1002/anie.201507363}, author = {Reddi, Rambabu N. and Prasad, Pragati K. and Sudalai, Arumugam} } @article { ISI:000368065300033, title = {Enantioselective synthesis of spirocyclohexadienones by NHC-catalyzed formal [3+3] annulation reaction of enals}, journal = {Angewandte Chemie-International Edition}, volume = {55}, number = {1}, year = {2016}, month = {JAN}, pages = {268-272}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {

The enantioselective synthesis of pyrazolone-fused spirocyclohexadienones was demonstrated by the reaction of alpha,beta-unsaturated aldehydes with alpha-arylidene pyrazolinones under oxidative N-heterocyclic carbene (NHC) catalysis. This atom-economic and formal [3+3] annulation reaction proceeds through a vinylogous Michael addition/spiroannulation/dehydrogenation cascade to afford spirocyclic compounds with an all-carbon quaternary stereocenter in moderate to good yields and excellent ee values. Key to the success of the reaction is the cooperative NHC-catalyzed generation of chiral alpha,beta-unsaturated acyl azoliums from enals, and base-mediated tandem generation of dienolate/enolate intermediates from pyrazolinones.

}, keywords = {annulation reactions, asymmetric catalysis, N-heterocyclic carbenes, organocatalysis, spiro compounds}, issn = {1433-7851}, doi = {10.1002/anie.201507802}, author = {Yetra, Santhivardhana Reddy and Mondal, Santigopal and Mukherjee, Subrata and Gonnade, Rajesh G. and Biju, Akkattu T.} } @article { ISI:000369072900005, title = {N-heterocyclic-carbene-catalyzed regioselective oxidative ring-opening of epoxides with aromatic aldehydes: a facile entry to alpha-acyloxyketones}, journal = {Asian Journal of Organic Chemistry}, volume = {5}, number = {1}, year = {2016}, month = {JAN}, pages = {48-51}, publisher = {WILEY-V C H VERLAG GMBH}, address = {POSTFACH 101161, 69451 WEINHEIM, GERMANY}, abstract = {

A high-yielding synthesis of -acyloxyketones using a N-heterocyclic-carbene (NHC)-catalyzed, oxidative ring-opening of epoxides with aromatic aldehydes is described. This regioselective, oxidative process utilizes a N-bromosuccinimide (NBS)/DMSO combination as the oxidant system and Et3N as the base under mild reaction conditions.

}, keywords = {aldehydes, epoxides, halogen oxidants, N-heterocyclic carbenes, oxygen}, issn = {2193-5807}, doi = {10.1002/ajoc.201500355}, author = {Reddi, Rambabu N. and Gontala, Arjun and Prasad, Pragati K. and Sudalai, Arumugam} } @article { ISI:000371566100001, title = {Recent advances in N-heterocyclic carbene (NHC)-catalysed benzoin reactions}, journal = {Beilstein Journal of Organic Chemistry}, volume = {12}, year = {2016}, month = {MAR}, pages = {444-461}, publisher = {BEILSTEIN-INSTITUT}, address = {TRAKEHNER STRASSE 7-9, FRANKFURT AM MAIN, 60487, GERMANY}, abstract = {

N-Heterocyclic carbenes (NHCs) have emerged as a powerful class of organocatalysts that mediate a variety of organic transformations. The Benzoin reaction constitutes one of the earliest known carbon-carbon bond-forming reactions catalysed by NHCs. The rapid growth of NHC catalysis in general has resulted in the development of a variety of benzoin and benzoin-type reactions. An overview of such NHC-catalysed benzoin reactions is presented.

}, keywords = {acyloin reaction, benzoin reaction, N-heterocyclic carbenes, organocatalysis, umpolung}, issn = {1860-5397}, doi = {10.3762/bjoc.12.47}, author = {Menon, Rajeev S. and Biju, Akkattu T. and Nair, Vijay} } @article {43862, title = {C(sp(3))-F, C(sp(2))-F and C(sp(3))-H bond activation at silicon(II) centers}, journal = {Chemical Communication}, volume = {53}, year = {2017}, month = {SEP}, chapter = {9850-9853}, abstract = {

Silylene [PhC(NtBu)(2)SiN(SiMe3)(2)] (1) cleaves the C(sp(3))-H and C-F bonds of acetophenone and 1,1,1-trifluoroacetophenone, respectively, under mild conditions. The reaction is initiated via a nucleophilic attack from the oxygen to the silicon atom followed by C-F/H bond cleavage. The scope of C-F bond activation has further been extended with C6F6 and C6F5CF3.

}, keywords = {Boron triple bond, C-F Bond, Fluorinated Building-Block, H Activation, Ketones, N-heterocyclic carbenes, Oxodative Addition, Perfluorinated Arenes, Selective Activation, Transition-Metal Centers}, issn = {1359-7345}, doi = {10.1039/c7cc05145j}, author = {Swamy, V. S. V. S. N. and Parvin, Nasrina and Raj, K. Vipin and Sen, Sakya S.} } @article {45769, title = {N-Heterocyclic carbene-catalyzed aldol-lactonization of ketoacids via dynamic kinetic resolution}, journal = {ACS Catalysis}, volume = {7}, year = {2017}, month = {JUN}, pages = {3995-3999}, type = {Article}, abstract = {

N-Heteroryclic carbene (NHC)-catalyzed enantioselective aldol lactonization of acyclic ketoacids, proceeding via dynamic kinetic resolution, is presented. The carbene generated from the chiral anninoinclanol-derived triazolium salt in the presence of LiCl was the key for the success of this transformation. The reaction allowed the diastereoselective and enantioselective synthesis of cyclopentane-fused beta-lactones having three contiguous stereocenters. The reaction products are shown to undergo substrate-controlled beta-lactone opening in the presence of amines to afford succinimide derivatives with four contiguous stereocenters.

}, keywords = {aldol lactonization, beta-lactones, DKR strategies, ketoacids, N-heterocyclic carbenes, organocatalysis}, issn = {2155-5435}, doi = {10.1021/acscatal.7b00681}, author = {Mondal, Santigopal and Mukherjee, Subrata and Das, Tamal Kanti and Gonnade, Rajesh and Biju, Akkattu T.} } @article {45609, title = {C-F bond activation by saturated NHC: mesoionic compound formation and its unprecedented adduct with B(C6F5)3}, journal = {Angewandte Chemie - International Edition}, volume = {58}, year = {2019}, month = {FEB}, pages = {2804-2808}, type = {Article}, abstract = {

The reaction of SIPr, [1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene] (1), with C6F6 led to the formation of an unprecedented mesoionic compound (2). The formation of 2 is made accessible by deprotonation of the SIPr backbone with simultaneous elimination of HF. The C-F bond para to the imidazolium ring in 2 is only of 1.258(4) {\r A}, which is the one of the shortest structurally authenticated C-F bonds known to date. The liberation of HF during the reaction is unequivocally proved by the addition of one more equivalent of SIPr, which leads to the imidazolium salt with the HF2- anion. To functionalize 2, the latter reacted with B(C6F5)3 to give an unusual donor{\textendash}acceptor compound, where the fluoride atom from the C6F5 moiety coordinates to B(C6F5)3 and the carbanion moiety remains unaffected. Such coordination susceptibility of the fluoride atom of a nonmetallic system to a main-group Lewis acid (Fnon-metal{\textrightarrow}BR3) is quite unprecedented.

}, keywords = {C-F activation, carbanions, N-heterocyclic carbenes, structure elucidation, Ylides}, issn = {1433-7851}, doi = {10.1002/anie.201814616}, author = {Pait, M. and Kundu, G. and Tothadi, S. and Karak, S. and Jain, S. and Vanka, K. and Sen, S. S.} } @article {46021, title = {N-Heterocyclic carbene-catalyzed umpolung of imines for the enantioselective synthesis of dihydroquinoxalines}, journal = {ACS Catalysis}, volume = {9}, year = {2019}, month = {MAY}, pages = {4065-4071}, type = {Article}, abstract = {

N-heterocyclic carbene (NHC) organocatalysis is widely employed for the umpolung of aldehydes and recently to the umpolung of Michael acceptors and aldimines. Described herein is the NHC-organocatalyzed umpolung of aldimines for the enantioselective synthesis of nitrogen heterocycles. The bisimines generated from the condensation of 1,2-phenylenediamines and salicylaldehydes undergo intramolecular cyclization in the presence of a chiral NHC catalyst, resulting in the formation of dihydroquinoxalines in moderate to good yields and er values. Detailed DFT studies shed light on the role of -OH groups in stabilizing the initially generated aza-Breslow intermediates via intramolecular hydrogen bonds. Preliminary photophysical studies on the synthesized dihydroquinoxalines revealed that these molecules can be used for the sensing of various acids and bases.

}, keywords = {dihydroquinoxalines, imines, N-heterocyclic carbenes, organocatalysis, umpolung}, issn = {2155-5435}, doi = {10.1021/acscatal.9b00737}, author = {Das, Tamal Kanti and Ghosh, Avik and Balanna, Kuruva and Behera, Pradipta and Gonnade, Rajesh G. and Marelli, Udaya Kiran and Das, Abhijit Kumar and Biju, Akkattu T.} } @article {47386, title = {NHC-catalyzed desymmetrization of N-aryl maleimides leading to the atroposelective synthesis of N-Aryl succinimides}, journal = {Angewandte Chemie-International Edition}, volume = {60}, year = {2021}, month = {MAY }, pages = {12264-12268}, type = {Article}, abstract = {

Although the construction of axially chiral C-C bonds leading to the atroposelective synthesis of biaryls and allied compounds are well-known, the related synthesis of compounds bearing axially chiral C-N bonds are relatively rare. Described herein is the N-heterocyclic carbene-catalyzed atroposelective synthesis of N-aryl succinimides having an axially chiral C-N bond via the desymmetrization of N-aryl maleimides. The NHC involved intermolecular Stetter-aldol cascade of dialdehydes with prochiral N-aryl maleimides followed by oxidation afforded N-aryl succinimides in good yields and ee values. Preliminary studies on rotation barrier for the C-N bond, the temperature dependence, and detailed DFT studies on mechanism are also provided.

}, keywords = {asymmetric catalysis, axial chirality, desymmetrization, N-heterocyclic carbenes, organocatalysis}, issn = {1433-7851}, doi = {10.1002/anie.202016938, Early Access Date = APR 2021}, author = {Barik, Soumen and Shee, Sayan and Das, Soumik and Gonnade, Rajesh G. and Jindal, Garima and Mukherjee, Subrata and Biju, Akkattu T.} }