@article {42448, title = {Efficient synthesis of gamma-keto sulfones by NHC-catalyzed intermolecular stetter reaction}, journal = {Organic Letters}, volume = {14}, year = {2012}, month = {MAY}, pages = {2830{\textendash}2833}, abstract = {

The N-heterocyclic carbene-catalyzed intermolecular Stetter reaction of aldehydes with α,β-unsaturated sulfones allows the atom-economic and selective formation of γ-keto sulfones in good yields. Key to the success of this unique transition-metal-free carbon{\textendash}carbon bond-forming reaction is the right choice of the NHC precursor and base. The reaction tolerates a broad range of different aldehydes.

}, doi = {10.1021/ol301045x}, author = {Bhunia, Anup and Yetra, Santhivardhana Reddy and Bhojgude, Sachin Suresh and Biju, Akkattu T.} } @article { ISI:000301985300008, title = {Recent advances in transition-metal-free carbon-carbon and carbon-heteroatom bond-forming reactions using arynes}, journal = {Chemical Society Reviews}, volume = {41}, number = {8}, year = {2012}, month = {JAN}, pages = {3140-3152}, publisher = {ROYAL SOC CHEMISTRY}, type = {Article}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

This tutorial review is aimed at highlighting recent developments in transition-metal-free carbon-carbon and carbon-heteroatom bond-forming reactions utilizing a versatile class of reactive intermediates, viz., arynes, which hold the potential for numerous applications in organic synthesis. Key to the success of the resurgence of interest in the rich chemistry of arynes is primarily the mild condition for their generation by the fluoride-induced 1,2-elimination of 2-(trimethylsilyl)aryl triflates. Consequently, arynes have been employed for the construction of multisubstituted arenes with structural diversity and complexity. The versatile transition-metal-free applications of arynes include cycloaddition reactions, insertion reactions and multicomponent reactions. In addition, arynes have found applications in natural product synthesis. Herein, we present a concise account of the major developments that occurred in this field during the past eight years.

}, issn = {0306-0012}, doi = {10.1039/c2cs15310f}, author = {Bhunia, Anup and Yetra, Santhivardhana Reddy and Biju, Akkattu T.} } @article { ISI:000326121700015, title = {Asymmetric N-heterocyclic carbene (NHC)-catalyzed annulation of modified enals with enolizable aldehydes}, journal = {Organic Letters}, volume = {15}, number = {20}, year = {2013}, month = {OCT}, pages = {5202-5205}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

N-Heterocyclic carbene (NHC)-catalyzed highly enantioselective lactonization of modified enals with enolizable aldehydes, proceeding via the alpha,beta-unsaturated acylazolium intermediates, is reported. The reaction results in the asymmetric synthesis of synthetically important 4,5-disubstituted dihydropyranones.

}, issn = {1523-7060}, doi = {10.1021/ol4026155}, author = {Yetra, Santhivardhana Reddy and Kaicharla, Trinadh and Kunte, Sunita S. and Gonnade, Rajesh G. and Biju, Akkattu T.} } @article { ISI:000319405900025, title = {Engaging isatins in solvent-free, sterically congested passerini reaction}, journal = {Green Chemistry}, volume = {15}, number = {6}, year = {2013}, month = {APR}, pages = {1608-1614}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

A facile, atom-economic and environmentally-benign protocol for the synthesis of biologically important oxindole derivatives in high yields has been demonstrated by employing isatins as carbonyl compound surrogates in a Passerini reaction carried out under solvent-free conditions. Moreover, electron-deficient phenols can also be used as the acid component in this reaction. In addition, the synthetic utility of the present methodology was examined by the one-pot synthesis of oxindoles with a free -OH group at the benzylic position.

}, issn = {1463-9262}, doi = {10.1039/c3gc40454d}, author = {Kaicharla, Trinadh and Yetra, Santhivardhana Reddy and Roy, Tony 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 {42442, title = {Synthesis of functionalized coumarins and quinolinones by NHC-catalyzed annulation of modified enals with heterocyclic C-H acids}, journal = {Journal of Organic Chemistry}, volume = {79}, year = {2014}, month = {APR}, pages = {4245{\textendash}4251}, abstract = {

N-Heterocyclic carbene (NHC) catalyzed lactonization and lactamization of 2-bromoenals with heterocyclic C{\textendash}H acids proceeding via the α,β-unsaturated acyl azolium intermediates is reported. The reaction furnished coumarin- or quinolinone-fused lactone/lactam derivatives. In addition, results of the enantioselective version of this reaction using chiral NHC are presented.

}, doi = {10.1021/jo500693h}, author = {Yetra, Santhivardhana Reddy and Roy, Tony and Bhunia, Anup and Porwal, Digvijay and Biju, Akkattu T.} } @article {42432, title = {Diastereoselective synthesis of cyclopentanone-fused spirooxindoles by N-heterocyclic carbene-catalyzed homoenolate annulation with isatilidenes}, journal = {Organic Chemistry Frontiers}, volume = {2}, year = {2015}, month = {SEP}, pages = {1584-1588}, abstract = {

N-Heterocyclic carbene (NHC)-catalyzed formal [3 + 2] annulation of α,β-unsaturated aldehydes with N-substituted isatilidenes resulting in the diastereoselective synthesis of cyclopentanone-fused spirooxindoles is demonstrated. Mechanistically, the reaction proceeds via the generation of homoenolate equivalent intermediates from NHC and enals, which on interception with isatilidenes afford spiroheterocyclic compounds bearing an all-carbon quaternary spiro-center in moderate to good yields and generally with high diastereoselectivity. Moreover, the functionalization of the spirooxindoles as well as the initial studies on the enantioselective version of this reaction are presented.

}, doi = {10.1039/C5QO00242G}, author = {Patra, Atanu and Bhunia, Anup and Yetra, Santhivardhana Reddy and Gonnade, Rajesh G. and Biju, Akkattu T.} } @article {45880, title = {Enantioselective synthesis of functionalized pyrazoles by NHC-catalyzed reaction of pyrazolones with alpha,beta-unsaturated aldehydes}, journal = {Organic Letters}, volume = {17}, year = {2015}, month = {MAR}, pages = {1417-1420}, type = {Article}, abstract = {

The N-heterocyclic carbene (NHC)-organocatalyzed enantioselective annulation reaction of pyrazolones with alpha,beta-unsaturated aldehydes proceeding via the chiral alpha,beta-unsaturated acyl azolium intermediates under oxidative conditions is presented. The reaction afforded dihydropyranone-fused pyrazoles in moderate to good yields and good er values under operationally simple and base-free conditions.

}, issn = {1523-7060}, doi = {10.1021/acs.orglett.5b00293}, author = {Yetra, Santhivardhana Reddy and Mondal, Santigopal and Suresh, Eringathodi and Biju, Akkattu T.} } @article {42436, title = {Recent advances in the N-heterocyclic carbene (NHC)-organocatalyzed stetter reaction and related chemistry}, journal = {Synthesis-Stuttgart}, volume = {47}, year = {2015}, month = {APR}, pages = {1357-1378}, abstract = {

Recent developments in the N-heterocyclic carbene (NHC)-catalyzed umpolung of aldehydes followed by their interception with activated carbon{\textendash}carbon double bonds, namely the Stetter reaction, are presented. Advances in the inter- and intramolecular versions of this reaction, enantioselective transformations as well as the use of unactivated olefins in this type of reaction are discussed.

}, doi = {10.1055/s-0034-1378692}, author = {Yetra, Santhivardhana Reddy and Patra, Atanu and Biju, Akkattu T.} } @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 {42431, title = {Synthesis of 4H-chromenes by an unexpected, K3PO4-mediated intramolecular rauhut{\textendash}currier type reaction}, journal = {Organic \& Biomolecular Chemistry}, volume = {14}, year = {2016}, month = {APR}, pages = {5612-5616}, abstract = {

In an attempt to develop the umpolung of Michael acceptors using chalcones having an enoate moiety under N-heterocyclic carbene (NHC) catalysis, a K3PO4-mediated intramolecular Rauhut{\textendash}Currier type reaction was observed. This C(sp2){\textendash}C(sp2) coupling reaction afforded the biologically important 4H-chromenes in moderate to good yields. It is likely that the enol ether functionality acts as the nucleophilic trigger in this reaction.

}, doi = {10.1039/C6OB00654J}, author = {Bhunia, Anup and Yetra, Santhivardhana Reddy and Gonnade, Rajesh G. and Biju, Akkattu T.} } @article {43798, title = {Organocatalytic enantioselective vinylogous michael-aidoi cascade for the synthesis of spirocyclic compounds}, journal = {Organic Letters}, volume = {19}, year = {2017}, month = {AUG}, pages = {4367-4370}, type = {Article}, abstract = {Enantioselective synthesis of pyrazolone-fused spirocyclohexenols by the secondary amine-catalyzed cascade reaction of alpha,beta-unsaturated aldehydes with alpha-arylidene pyrazolinones is reported. This formal [3 + 3] organocascade reaction proceeds through a vinylogous Michael-aldol sequence to furnish the spiroheterocycles with three stereocenters including an all-carbon quaternary center in good yields and selectivities. The catalytic generation of alpha,beta-unsaturated iminium ions from enals and tandem dienolate/enolate formation from pyrazolinones are the key for the success of this spiroannulation reaction.}, doi = {10.1021/acs.orglett.7b02085}, author = {Mondal, Santigopal and Mukherjee, Subrata and Yetra, Santhivardhana Reddy and Gonnade, Rajesh G. and Biju, Akkattu T.} }