@article {42467, title = {Novel synthesis of highly functionalized pyrazolines and pyrazoles by triphenylphosphine mediated reaction of dialkyl azodicarboxylate with allenic esters}, journal = {Organic Letters}, volume = {8}, year = {2006}, month = {MAY}, pages = {2213{\textendash}2216}, type = {Article}, abstract = {

Reaction of the Huisgen zwitterion, derived from triphenylphosphine and dialkyl azodicarboxylate, with allenic esters affords highly functionalized pyrazolines and pyrazoles. The crystal structure of pyrazoline derivative 7a showed extensive C-H{\textperiodcentered}{\textperiodcentered}{\textperiodcentered}O interactions. Pyrazole formation proceeds via a novel nitrogen to carbon migration of the carboalkoxy group.

}, doi = {10.1021/ol0604623}, author = {Nair, Vijay and Biju, Akkattu T. and Mohanan, Kishor and Eringathodi, Suresh} } @article {42463, title = {Novel reaction of the {\textquotedblleft}huisgen zwitterion{\textquotedblright} with chalcones and dienones: an efficient strategy for the synthesis of pyrazoline and pyrazolopyridazine derivatives}, journal = {Angewandte Chemie-International Edition}, volume = {46}, year = {2007}, month = {MAR}, pages = {2070{\textendash}2073}, type = {Article}, abstract = {

Two unexpected transformations: The reaction of the Huisgen zwitterion derived from triphenylphosphane and diisopropyl azodicarboxylate (DIAD) with chalcones affords functionalized pyrazolines. In contrast, the reaction with dienones affords pyrazolopyridazines, presumably by Diels{\textendash}Alder reaction of the initially formed pyrazoline with excess DIAD (see scheme).

}, keywords = {chalcones; nitrogen heterocycles; pyrazolines; synthetic methods; zwitterions}, doi = {10.1002/anie.200604025}, author = {Nair, Vijay and Biju, Akkattu T. and Mathew, Smitha C. and Eringathodi, Suresh} } @article {42457, title = {N-heterocyclic carbene-catalyzed hydroacylation of unactivated double bonds}, journal = {Journal of the American Chemical Society}, volume = {131}, year = {2009}, month = {SEP}, pages = {14190{\textendash}14191}, abstract = {

An intramolecular N-heterocyclic carbene (NHC)-catalyzed hydroacylation of unactivated double bonds is reported. Systematic variation of the catalyst structure revealed an N-mesitylthiazolylidene annulated with a seven-membered ring to be especially reactive. This NHC enables a unique C-C bond-forming reaction to afford substituted chroman-4-ones in moderate to excellent yields, even ones containing all-carbon quaternary centers.

}, doi = {10.1021/ja906361g}, author = {Hirano, Keiichi and Biju, Akkattu T. and Piel, Isabel and Glorius, Frank} } @article {42453, title = {N-heterocyclic carbene-catalyzed cascade reaction involving the hydroacylation of unactivated alkynes}, journal = {Journal of the American Chemical Society}, volume = {132}, year = {2010}, month = {APR}, pages = {5970{\textendash}5971}, abstract = {

The N-heterocyclic carbene (NHC)-catalyzed hydroacylation of unactivated alkynes to provide α,β-unsaturated ketones is reported. In addition, a rare case of an efficient and selective dually NHC-catalyzed cascade reaction involving the hydroacylation of alkynes and a subsequent intermolecular Stetter reaction allows the formation of chromanones containing a 1,4-diketone moiety.

}, doi = {10.1021/ja102130s}, author = {Biju, Akkattu T. and Wurz, Nathalie E. and Glorius, Frank} } @article { ISI:000295259700041, title = {N-Heterocyclic carbene catalyzed umpolung of michael acceptors for intermolecular reactions}, journal = {Angewandte Chemie-International Edition}, volume = {50}, number = {36}, year = {2011}, month = {AUG}, pages = {8412-8415}, publisher = {WILEY-V C H VERLAG GMBH}, address = {BOSCHSTRASSE 12, D-69469 WEINHEIM, GERMANY}, abstract = {

eahciM! The N-heterocyclic carbene catalyzed umpolung of Michael acceptors proceeds through the formation of a deoxy-Breslow intermediate (see scheme; EWG=electron-withdrawing group). This nucleophilic species can react with other Michael acceptors in an intermolecular fashion, thereby resulting in the formation of homo- or heterodimeric olefins. This {\textquotedblleft}Michael umpolung{\textquotedblright} should become a valuable method for the formation of densely functionalized olefins.

}, keywords = {carbenes, Michael acceptors, nitrogen heterocycles, organocatalysis, umpolung}, issn = {1433-7851}, doi = {10.1002/anie.201103555}, author = {Biju, Akkattu T. and Padmanaban, Mohan and Wurz, Nathalie E. and Glorius, Frank} } @article {42450, title = {N-heterocyclic carbene-catalyzed cross-coupling of aromatic aldehydes with activated alkyl halides}, journal = {Organic Letters}, volume = {13}, year = {2011}, month = {NOV}, pages = {98{\textendash}101}, abstract = {

N-Heterocyclic carbene-catalyzed umpolung of aldehydes followed by their interception with diarylbromomethanes has been reported. This conceptually novel transition-metal-free cross-coupling of aldehydes with alkyl halides works well at low catalyst loadings and under mild reaction conditions leading to the formation of diaryl acetophenone derivatives in good yields. In addition, α-halo ketones and esters can also be used as aldehyde reaction partners.

}, doi = {10.1021/ol102626p}, author = {Padmanaban, Mohan and Biju, Akkattu T. and Glorius, Frank} } @article { ISI:000317327900086, title = {NHC-Catalyzed reaction of enals with hydroxy chalcones: diastereoselective synthesis of functionalized coumarins}, journal = {Organic Letters}, volume = {15}, number = {7}, year = {2013}, month = {APR}, pages = {1756-1759}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The N-heterocyclic carbene-catalyzed annulation of enals with 2{\textquoteright}-hydroxy chalcones afford cyclopentane-fused coumarin derivatives with an excellent level of diastereocontrol. The reaction tolerates a broad range of functional groups; 25 examples are given, and a preliminary mechanistic investigation is provided.

}, issn = {1523-7060}, doi = {10.1021/ol400562z}, author = {Bhunia, Anup and Patra, Atanu and Puranik, Vedavati G. and Biju, Akkattu T.} } @article { ISI:000344459400014, title = {N-Heterocyclic carbene-catalyzed enantioselective synthesis of functionalized cyclopentenes via alpha,beta-unsaturated acyl azoliums}, journal = {Chemical Communications}, volume = {50}, number = {93}, year = {2014}, month = {OCT}, pages = {14539-14542}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Highly enantioselective NHC-organocatalyzed synthesis of functionalized cyclopentenes proceeding via alpha,beta-unsaturated acyl azolium intermediates is reported. The organocascade reaction of modified enals with malonic ester derivatives having a gamma-benzoyl group involves the Michael-intramolecular aldol-beta-lactonization-decarboxylation sequence to deliver cyclopentenes in good yields and excellent ee values.

}, issn = {1359-7345}, doi = {10.1039/c4cc07433e}, author = {Mondal, Santigopal and Yetra, Santhivardhana Reddy and Patra, Atanu and Kunte, Sunita S. and Gonnade, Rajesh G. and Biju, Akkattu T.} } @article {42434, title = {N-Heterocyclic carbene-catalyzed diastereoselective synthesis of β-lactone-fused cyclopentanes using homoenolate annulation reaction}, journal = {Chemical Communications}, volume = {51}, year = {2015}, month = {MAY}, pages = {9559-9562}, abstract = {

NHC-catalyzed annulation of enals with 2-enoylpyridines or 2-enoylpyridine\ N-oxides leading to the diastereoselective synthesis of β-lactone-fused cyclopentanes is reported. The reaction proceeds\ via\ the generation of homoenolate equivalent intermediates and tolerates a broad range of functional groups.

}, doi = {10.1039/C5CC02960K}, author = {Mukherjee, Subrata and Mondal, Santigopal and Patra, Atanu and Gonnade, Rajesh G. and Biju, Akkattu T.} } @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 {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 {44644, title = {N-Heterocyclic carbene-catalyzed enantioselective synthesis of spiro-glutarimides via alpha,beta-unsaturated acylazoliums}, journal = {Organic Letters}, volume = {20}, year = {2018}, month = {AUG}, pages = {4499-4503}, abstract = {

NHC-catalyzed enantioselective [3 + 3] spiro-annulation of alpha,beta-unsaturated aldehydes with cyclic beta-ketoamides allowing the preparation of synthetically and biologically important spiro-glutarimide derivatives has been reported. The interception of the ketoamides with catalytically generated chiral alpha,beta-unsaturated acylazoliums proceeds in a Michael addition-intramolecular amidation pathway to deliver the spirocyclic products with good yield, diastereoselectivity, and enantioselectivity.

}, issn = {1523-7060}, doi = {10.1021/acs.orglett.8b01799}, author = {Mondal, Santigopal and Ghosh, Arghya and Mukherjee, Subrata and Biju, Akkattu T.} } @article {44535, title = {N-Heterocyclic carbene-catalyzed michael-michael-lactonization cascade for the enantioselective synthesis of tricyclic delta-lactones}, journal = {Organic Letters}, volume = {20}, year = {2018}, month = {MAY}, pages = {2952-2955}, abstract = {

Enantioselective synthesis of tricyclic delta-lactones with three contiguous stereocenters has been demonstrated by the N-heterocyclic carbene (NHC)-catalyzed functionalization of benzylic C(sp(3))-H bonds. The NHC-catalyzed reaction of enals with dinitrotoluene derivatives under oxidative conditions proceeds via the chiral alpha,beta-unsaturated acylazoliums and produces the delta-lactones in good yields and excellent diastereoselectivity and enantioselectivity. This mild and atom-economic cascade reaction takes place in a Michael/Michael/lactonization sequence and tolerates a broad range of functional groups.

}, issn = {1523-7060}, doi = {10.1021/acs.orglett.8b00998}, author = {Mukherjee, Subrata and Ghosh, Arghya and Marelli, Udaya Kiran and Biju, Akkattu T.} } @article {44621, title = {N-Heterocyclic carbene-catalyzed synthesis of alpha-trifluoromethyl esters}, journal = {Organic Letters}, volume = {20}, year = {2018}, month = {JUL}, pages = {3897-3901}, abstract = {

The N-heterocyclic carbene (NHC)-catalyzed trifluoromethylation of alpha-chloro aldehydes was developed, allowing straightforward access to valuable alpha-trifluoromethyl ester derivatives. The unique combination of an electrophilic trifluoromethylation reagent with NHC catalysis was the key for the functionalization of a broad range of alpha-chloro aldehydes, and the products are formed in moderate to good yields. Investigations of the enantioselective version of this reaction afforded the enantioenriched products in moderate yields with good ee values.

}, issn = {1523-7060}, doi = {10.1021/acs.orglett.8b01482}, author = {Gelat, Fabien and Patra, Atanu and Pannecoucke, Xavier and Biju, Akkattu T. and Poisson, Thomas and Besset, Tatiana} } @inbook {47494, title = {N-heterocyclic carbene-catalyzed stetter reaction and related chemistry}, booktitle = {N-Heterocyclic Carbenes in Organocatalysis}, year = {2019}, publisher = {Wiley}, organization = {Wiley}, chapter = {Chapter 3}, abstract = {The reversal of normal mode of reactivity (umpolung) of aldehydes is the most important application of N-heterocyclic carbenes (NHCs) in organocatalytic transformations. The benzoin condensation and the Stetter reaction are the two historic reactions where NHC reacts with aldehyde to generate acyl anion equivalent, which is subsequently intercepted with another molecule of carbonyl compound or Michael acceptor leading to the formation of the benzoin/Stetter products. The objective of this chapter is to provide an overview on NHC-catalyzed Stetter reaction and related chemistry. The development of various chiral catalysts for enantioselective intra- or intermolecular Stetter reaction has been described. Additionally, recent progress on NHC-catalyzed addition of aldehyde to unactivated multiple bonds in the hydroacylation reaction has been demonstrated.}, issn = {Online ISBN: 9783527809042}, doi = {10.1002/9783527809042.ch3}, author = {Mondal, Santigopal and Yetra, Santhivardhana R. and Biju, Akkattu T.} } @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 {46899, title = {N-heterocyclic carbene catalysis exploiting oxidative imine umpolung for the generation of imidoyl azoliums}, journal = {Journal of Organic Chemistry}, volume = {85}, year = {2020}, month = {APR }, pages = {5114-5121}, type = {Article}, abstract = {

Although NHC-catalyzed umpolung of imines are known, the related reactions under oxidative conditions are limited. Described herein is the two-step process involving the initial formation of aldimines from the corresponding aldehydes and 2-amino benzyl alcohols followed by NHC-catalyzed cyclization proceeding via the imidoyl azoliums under oxidative conditions. The reaction allowed the synthesis of trifluoromethylated 3,1-benzoxazines in good yields and broad scope. The role of NHC in the intramolecular cyclization and preliminary mechanistic experiments are also provided.

}, issn = {0022-3263}, doi = {10.1021/acs.joc.0c00360}, author = {Das, Tamal Kanti and Madica, Krishnaprasad and Krishnan, Jagadeesh and Marelli, Udaya Kiran and Biju, Akkattu T.} } @article {47144, title = {N-heterocyclic carbene (NHC)-catalyzed transformations for the synthesis of heterocycles}, journal = {Progress in Heterocyclic Chemistry}, volume = {31}, year = {2020}, month = {JAN}, pages = {1-82}, type = {Book Chapter}, abstract = {

N-heterocyclic carbene (NHC)-based organocatalysis has been widely used for unconventional access to various target molecules. The use of chiral NHCs in the process results in the enantioselective synthesis of various heterocycles. The underlying principle of many of the NHC-catalyzed reactions is the remarkable ability of NHCs to reverse the normal mode of reactivity of aldehydes (umpolung). NHCs can catalyze transformations proceeding via the umpolung or nonumpolung mode for the synthesis of various functionalized molecules. The recent advances in the application of NHCs for the synthesis of various heterocyclic compounds are highlighted in this chapter.

}, keywords = {aldehyde umpolung, Aldimine umpolung, benzoin reaction, Breslow intermediates, Enantioselective synthesis, Heterocyclic synthesis, N-Heterocyclic carbene, Stetter reaction}, doi = {10.1016/B978-0-12-819962-6.00001-4}, author = {Das, Tamal Kanti 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.} } @article {48760, title = {NHC-catalyzed enantioselective synthesis of tetracyclic δ-lactones by (4+2) annulation of ortho-quinodimethanes with activated ketones}, journal = {Organic Letters}, volume = {25}, year = {2023}, month = {OCT }, pages = {7852-7857}, type = {Article}, abstract = {

The N-heterocyclic carbene (NHC)-catalyzed generation of ortho-quinodimethanes (o-QDMs) from 9H-fluorene-1-carbaldehydes followed by the interception with activated ketones resulting in the enantioselective synthesis of tetracyclic delta-lactones is presented. High diastereoselectivity of products, remote C-(sp(3))-H functionalization, broad substrate scope, and mild reaction conditions are the notable features of the present (4 + 2) annulation.

}, issn = {1523-7060}, doi = {10.1021/acs.orglett.3c03076}, author = {Sarkar, Deeptanu and Barik, Shilpa and Shee, Sayan and Gonnade, Rajesh G. and Biju, Akkattu T.} } @article {48752, title = {N-heterocyclic carbene-catalyzed atroposelective synthesis of N-N axially chiral 3-amino quinazolinones}, journal = {ACS Catalysis}, volume = {13}, year = {2023}, month = {JUN }, pages = {8752-8759}, type = {Article}, abstract = {

Although the atroposelective synthesisof biaryls and related compoundsbearing axially chiral C-C bonds is well-known, the synthesisof axially chiral C-N bond-containing compounds is relativelyless explored, and the construction of axially chiral N-N bondshas received only scant attention. Demonstrated herein is the N-heterocycliccarbene (NHC)-catalyzed selective amidation reaction, leading to theatroposelective synthesis of N-N axially chiral 3-amino quinazolinones.The NHC-catalyzed reaction of quinazolinones containing a free N-Hmoiety with \& alpha;,\& beta;-unsaturated aldehydes under oxidativeconditions furnished the atropisomeric quinazolinone derivatives undermild conditions and broad scope. Preliminary studies on experimentaland density functional theory-based N-N rotational barrierdetermination are also presented.

}, keywords = {amino quinazolinones, asymmetriccatalysis, axial chirality, N-heterocycliccarbenes, organocatalysis}, issn = {2155-5435}, doi = {10.1021/acscatal.3c01709}, author = {Balanna, Kuruva and Barik, Soumen and Barik, Shilpa and Shee, Sayan and Manoj, Niket and Gonnade, Rajesh G. and Biju, Akkattu T.} }