2020
S. Varga; P. Angyal; G. Martin; O. Egyed; T. Holczbauer; T. Soós
Total Syntheses of (−)-Minovincine and (−)-Aspidofractinine through a Sequence of Cascade Reactions Journal Article
In: Angewandte Chemie - International Edition, vol. 59, no. 32, pp. 13547-13551, 2020.
@article{Varga202013547,
title = {Total Syntheses of (−)-Minovincine and (−)-Aspidofractinine through a Sequence of Cascade Reactions},
author = {S. Varga and P. Angyal and G. Martin and O. Egyed and T. Holczbauer and T. Soós},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85085900974&doi=10.1002%2fanie.202004769&partnerID=40&md5=63fae7eac53f87f7c15894d345695a7d},
doi = {10.1002/anie.202004769},
year = {2020},
date = {2020-01-01},
urldate = {2020-01-01},
journal = {Angewandte Chemie - International Edition},
volume = {59},
number = {32},
pages = {13547-13551},
abstract = {We report 8-step syntheses of (−)-minovincine and (−)-aspidofractinine using easily available and inexpensive reagents and catalyst. A key element of the strategy was the utilization of a sequence of cascade reactions to rapidly construct the penta- and hexacyclic frameworks. These cascade transformations included organocatalytic Michael-aldol condensation, a multistep anionic Michael-SN2 cascade reaction, and Mannich reaction interrupted Fischer indolization. To streamline the synthetic routes, we also investigated the deliberate use of steric effect to secure various chemo- and regioselective transformations. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.},
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G. Martin; P. Angyal; O. Egyed; S. Varga; T. Soós
Total Syntheses of Dihydroindole Aspidosperma Alkaloids: Reductive Interrupted Fischer Indolization Followed by Redox Diversification Journal Article
In: Organic Letters, vol. 22, no. 12, pp. 4675-4679, 2020.
@article{Martin20204675,
title = {Total Syntheses of Dihydroindole Aspidosperma Alkaloids: Reductive Interrupted Fischer Indolization Followed by Redox Diversification},
author = {G. Martin and P. Angyal and O. Egyed and S. Varga and T. Soós},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85086572635&doi=10.1021%2facs.orglett.0c01472&partnerID=40&md5=2ba602067c507b05209bbe2ff847a8f7},
doi = {10.1021/acs.orglett.0c01472},
year = {2020},
date = {2020-01-01},
urldate = {2020-01-01},
journal = {Organic Letters},
volume = {22},
number = {12},
pages = {4675-4679},
abstract = {We report a novel reductive interrupted Fischer indolization process for the concise assembly of the 20-oxoaspidospermidine framework. This rapid complexity generating route paves the way toward various dihydroindole Aspidosperma alkaloids with different C-5 side chain redox patterns. The end-game redox modulations were accomplished by modified Wolff-Kishner reaction and photo-Wolff rearrangement, enabling the total synthesis of (-)-aspidospermidine, (-)-limaspermidine, and (+)-17-demethoxy-N-acetylcylindrocarine and the formal total synthesis of (-)-1-acetylaspidoalbidine. Copyright © 2020 American Chemical Society.},
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pubstate = {published},
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}
2017
A. Bacsó; M. Szigeti; S. Varga; T. Soós
Bifunctional Thiourea-Catalyzed Stereoablative Retro-Sulfa-Michael Reaction: Concise and Diastereoselective Access to Chiral 2,4-Diarylthietanes Journal Article
In: Synthesis (Germany), vol. 49, no. 2, pp. 429-439, 2017.
@article{Bacsó2017429,
title = {Bifunctional Thiourea-Catalyzed Stereoablative Retro-Sulfa-Michael Reaction: Concise and Diastereoselective Access to Chiral 2,4-Diarylthietanes},
author = {A. Bacsó and M. Szigeti and S. Varga and T. Soós},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84991241342&doi=10.1055%2fs-0036-1588612&partnerID=40&md5=def2c2c9a151dcd0034822a5c7a0f8ad},
doi = {10.1055/s-0036-1588612},
year = {2017},
date = {2017-01-01},
urldate = {2017-01-01},
journal = {Synthesis (Germany)},
volume = {49},
number = {2},
pages = {429-439},
abstract = {Owing to the chiral recognition capacity of bifunctional thioureas, a stereoablative retro-sulfa-Michael reaction has been developed. Utilization of a biphasic system enabled us to render the process catalytic. The usefulness of this methodology was further illustrated by the diastereoselective synthesis of all possible stereoisomers of 2,4-diarylthiethanes. ©2017 Georg Thieme Verlag Stuttgart, New York.},
keywords = {},
pubstate = {published},
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}
2016
A. Madarász; Z. Dósa; S. Varga; T. Soós; A. Csámpai; I. Pápai
Thiourea Derivatives as Brønsted Acid Organocatalysts Journal Article
In: ACS Catalysis, vol. 6, no. 7, pp. 4379-4387, 2016.
@article{Madarász20164379,
title = {Thiourea Derivatives as Brønsted Acid Organocatalysts},
author = {A. Madarász and Z. Dósa and S. Varga and T. Soós and A. Csámpai and I. Pápai},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84977090904&doi=10.1021%2facscatal.6b00618&partnerID=40&md5=28aa2b18b9c0bcc7237c5255aada5538},
doi = {10.1021/acscatal.6b00618},
year = {2016},
date = {2016-01-01},
urldate = {2016-01-01},
journal = {ACS Catalysis},
volume = {6},
number = {7},
pages = {4379-4387},
abstract = {Combined computational-experimental studies were carried out to parallel two mechanistic models for tetrahydropyranylation of alcohols catalyzed by Schreiner's thiourea. The results challenge the common mechanistic view that the catalytic effect is related to stabilizing double hydrogen-bonding interactions between the thiourea and the alcohol, which promote the attack on 3,4-dihydro-2H-pyran (DHP) (hydrogen bonding (HB) mechanism). In the alternative mechanism that we propose, thiourea acts as a Brønsted acid, protonating DHP to form an oxacarbenium ion, which reacts with the alcohol (Brønsted acid (BA) mechanism). Computations point to clear preference of transition states associated with the BA mechanism and, accordingly, predict similar catalytic activity for N-methylated thiourea and thiouracil. These predictions are confirmed experimentally. Reactions with deuterated alcohols yield both syn and anti products, providing further support for the Brønsted acid mechanism. © 2016 American Chemical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2015
S. Varga; G. Jakab; A. Csámpai; T. Soós
In: Journal of Organic Chemistry, vol. 80, no. 18, pp. 8990-8996, 2015.
@article{Varga20158990,
title = {Iterative Coupling of Two Different Enones by Nitromethane Using Bifunctional Thiourea Organocatalysts. Stereocontrolled Assembly of Cyclic and Acyclic Structures},
author = {S. Varga and G. Jakab and A. Csámpai and T. Soós},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84941921452&doi=10.1021%2facs.joc.5b01474&partnerID=40&md5=e414d158a193498d05ac7b40e4804287},
doi = {10.1021/acs.joc.5b01474},
year = {2015},
date = {2015-01-01},
urldate = {2015-01-01},
journal = {Journal of Organic Chemistry},
volume = {80},
number = {18},
pages = {8990-8996},
abstract = {An organocatalytic iterative assembly line has been developed in which nitromethane was sequentially coupled with two different enones using a combination of pseudoenantiomeric cinchona-based thiourea catalysts. Application of unsaturated aldehydes and ketones in the second step of the iterative sequence allows the construction of cyclic syn-ketols and acyclic compounds with multiple contiguous stereocenters. The combination of the multifunctional substrates and ambident electrophiles rendered some organocatalytic transformations possible that have not yet been realized in bifunctional noncovalent organocatalysis. © 2015 American Chemical Society.},
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pubstate = {published},
tppubtype = {article}
}
2012
G. Tárkányi; P. Király; T. Soós; S. Varga
Active conformation in amine-thiourea bifunctional organocatalysis preformed by catalyst aggregation Journal Article
In: Chemistry - A European Journal, vol. 18, no. 7, pp. 1918-1922, 2012.
@article{Tárkányi20121918,
title = {Active conformation in amine-thiourea bifunctional organocatalysis preformed by catalyst aggregation},
author = {G. Tárkányi and P. Király and T. Soós and S. Varga},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84856695332&doi=10.1002%2fchem.201102701&partnerID=40&md5=338aa8ee97287b2b50d03be84ec97856},
doi = {10.1002/chem.201102701},
year = {2012},
date = {2012-01-01},
urldate = {2012-01-01},
journal = {Chemistry - A European Journal},
volume = {18},
number = {7},
pages = {1918-1922},
abstract = {Self-activation: Takemoto's catalyst gains access to its active conformation by equilibrating between its hydrogen-bonded intra- and intermolecular interactions in apolar aprotic solvents. By destabilization of the inactive monomeric conformations, the extended anti-anti thiourea conformation is preformed in the assembly. On leaving the assembly, this transient conformation has a structural preference to become a catalytically active monomeric species that has the potency for dual activation (see scheme). © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2011
S. Varga; G. Jakab; L. Drahos; T. Holczbauer; M. Czugler; T. Soós
In: Organic Letters, vol. 13, no. 20, pp. 5416-5419, 2011.
@article{Varga20115416,
title = {Double diastereocontrol in bifunctional thiourea organocatalysis: Iterative Michael-Michael-Henry sequence regulated by the configuration of chiral catalysts},
author = {S. Varga and G. Jakab and L. Drahos and T. Holczbauer and M. Czugler and T. Soós},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-80054695939&doi=10.1021%2fol201559j&partnerID=40&md5=8884f1f7610d8c16e18a8a3ab873a1a0},
doi = {10.1021/ol201559j},
year = {2011},
date = {2011-01-01},
urldate = {2011-01-01},
journal = {Organic Letters},
volume = {13},
number = {20},
pages = {5416-5419},
abstract = {The importance and reactivity consequences of the double diastereocontrol in noncovalent bifunctional organocatalysis were studied. The results suggest that the bifunctional thioureas can have synthetic limitations in multicomponent domino or autotandem catalysis. Nevertheless, we provided a means to exploit this behavior and used the configuration of the chiral catalyst as a control element in organo-sequential reactions. © 2011 American Chemical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2010
P. Király; T. Soós; S. Varga; B. Vakulya; G. Tárkányi
Self-association promoted conformational transition of (3R,4S,8R,9R)-9-[(3, 5-bis(trifluoromethyl)phenyl))-thiourea](9-deoxy)-epi-cinchonine Journal Article
In: Magnetic Resonance in Chemistry, vol. 48, no. 1, pp. 13-19, 2010.
@article{Király201013,
title = {Self-association promoted conformational transition of (3R,4S,8R,9R)-9-[(3, 5-bis(trifluoromethyl)phenyl))-thiourea](9-deoxy)-epi-cinchonine},
author = {P. Király and T. Soós and S. Varga and B. Vakulya and G. Tárkányi},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-73949129298&doi=10.1002%2fmrc.2531&partnerID=40&md5=ef682695ad1ce72ce06f871a043a3b4b},
doi = {10.1002/mrc.2531},
year = {2010},
date = {2010-01-01},
urldate = {2010-01-01},
journal = {Magnetic Resonance in Chemistry},
volume = {48},
number = {1},
pages = {13-19},
abstract = {The conformational diversity of the (3R,4S,8R,9R)-9-[(3,5- bis(trifluoromethyl)phenyl))-thiourea](9-deoxy)-epi-cinchonine organocatalyst is discussed. Low-temperature NMR experiments confirmed a self-association process, which promotes the quinoline rotation between two intramolecularly hydrogen-bonded monomeric conformers of the catalyst. The balanced population of the coexisting monomeric and dimeric species allowed us to conduct a structural study of a rather complex conformational dynamics of the pure catalyst. The study is extended by a comparison with other members of the bifunctional amine-thiourea organocatalyst family. Changes in themolecular structure of the catalysts influence the interplaybetween intraand intermolecular hydrogen bonding, and yield different extent of catalyst self-association. By assessing the conformation of the individual states, we established the thermodynamic model of a self-association promoted conformational transition. Copyright © 2009 John Wiley & Sons, Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2008
G. Tárkányi; P. Király; S. Varga; B. Vakulya; T. Soós
Edge-to-face CH/π aromatic interaction and molecular self-recognition in epi-cinchona-based bifunctional thiourea organocatalysis Journal Article
In: Chemistry - A European Journal, vol. 14, no. 20, pp. 6078-6086, 2008.
@article{Tárkányi20086078,
title = {Edge-to-face CH/π aromatic interaction and molecular self-recognition in epi-cinchona-based bifunctional thiourea organocatalysis},
author = {G. Tárkányi and P. Király and S. Varga and B. Vakulya and T. Soós},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-53849086148&doi=10.1002%2fchem.200800197&partnerID=40&md5=793cd2313eaaada5b1ee338807489713},
doi = {10.1002/chem.200800197},
year = {2008},
date = {2008-01-01},
urldate = {2008-01-01},
journal = {Chemistry - A European Journal},
volume = {14},
number = {20},
pages = {6078-6086},
abstract = {The impact of cooperativity between intermolecular interactions is demonstrated by the molecular self-recognition properties of highly enantioselective epi-cinchona bifunctional thiourea organocatalysts. Low-temperature NMR experiments in inert solvents have revealed two sets of nonequivalent resonances in equal population for thiourea-modified members of the epi-quinine and epi-quinidine families. In solution, the predominance of an asymmetric (C1) dimeric self-assembly with noteworthy structural motifs became evident: simultaneous intra-and intermolecular thiourea hydrogen bonding and a CH/π interaction were observed. Both the stereochemical and the diverse conformational features of the system favor the observed quinoline T-shaped aromatic π-π stacking interaction. The structure findings are supported by quantitative protonproton distance data that were available from NOE buildup curves. The 3D structure of the dimeric assembly has been modeled in agreement with the H-H distance restraints. Owing to the geometrical preference associated with the dimerization process, the self-assembled bifunctional system is interpreted as a charge-transfer complex with the potential for catalyst self-activation. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
B. Vakulya; S. Varga; T. Soós
In: Journal of Organic Chemistry, vol. 73, no. 9, pp. 3475-3480, 2008.
@article{Vakulya20083475,
title = {Epi-cinchona based thiourea organocatalyst family as an efficient asymmetric Michael addition promoter: Enantioselective conjugate addition of nitroalkanes to chalcones and α,β-unsaturated N-acylpyrroles},
author = {B. Vakulya and S. Varga and T. Soós},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-43449135616&doi=10.1021%2fjo702692a&partnerID=40&md5=84615d7c24ff15f0956458d5994bf5be},
doi = {10.1021/jo702692a},
year = {2008},
date = {2008-01-01},
urldate = {2008-01-01},
journal = {Journal of Organic Chemistry},
volume = {73},
number = {9},
pages = {3475-3480},
abstract = {(Chemical Equation Presented) A small set of easily available epi-cinchona based thiourea organocatalysts have been synthesized and tested in enantioselective Michael addition of nitroalkanes to chalcones. These bifunctional catalyst systems promoted the conjugate additions with high enantioselectivities and chemical yields. The extension of this methodology was further explored to encompass α,β-unsaturated N-acylpyrroles, as a chalcone mimic. Functionally, the N-acylpyrrole moiety in the adduct acts as an ester surrogate; therefore, it can easily be transformed to various valuable and biologically relevant compounds. This approach allowed the concise stereoselective synthesis of (R)-rolipram. © 2008 American Chemical Society.},
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pubstate = {published},
tppubtype = {article}
}
2005
B. Vakulya; S. Varga; A. Csámpai; T. Soós
Highly enantioselective conjugate addition of nitromethane to chalcones using bifunctional cinchona organocatalysts Journal Article
In: Organic Letters, vol. 7, no. 10, pp. 1967-1969, 2005.
@article{Vakulya20051967,
title = {Highly enantioselective conjugate addition of nitromethane to chalcones using bifunctional cinchona organocatalysts},
author = {B. Vakulya and S. Varga and A. Csámpai and T. Soós},
url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-19544393388&doi=10.1021%2fol050431s&partnerID=40&md5=d00104af201e2c97441bfe70232cbece},
doi = {10.1021/ol050431s},
year = {2005},
date = {2005-01-01},
urldate = {2005-01-01},
journal = {Organic Letters},
volume = {7},
number = {10},
pages = {1967-1969},
abstract = {(Chemical Equation Presented) Cinchona alkaloid-derived chiral bifunctional thiourea organocatalysts were synthesized and applied in the Michael addition between nitromethane and chalcones with high ee and chemical yields. © 2005 American Chemical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}