0000000001307188
AUTHOR
Pankaj Chauhan
showing 30 related works from this author
Asymmetric Synthesis of Five-Membered Spiropyrazolones via N-Heterocyclic Carbene (NHC)-Catalyzed [3+2] Annulations
2016
A new synthetic strategy for the asymmetric synthesis of five-membered spiropyrazolones via N-heterocyclic carbene-catalyzed [3+2] annulations employing enals and unsaturated pyrazolones as substrates has been developed. The new protocol allows the flexible variation of all four substituents of the pharmaceutically important spiropyrazolones in moderate to very good yields and in most cases with excellent diastereoselectivities and good to excellent enantioselectivities.
Asymmetric Synthesis of Spiro β-Lactamsviaa Squaramide- Catalyzed Sulfa-Michael Addition/Desymmetrization Protocol
2016
An efficient asymmetric synthesis of spirocyclohexenone β-lactams bearing three contiguous stereocenters has been achieved in moderate to good yields and high stereoselectivities. The protocol involves the combination of a squaramide-catalyzed sulfa-Michael addition under desymmetrization via a dynamic kinetic resolution of racemic 2,5-cyclohexadienones.
Asymmetric Synthesis of Spiro Tetrahydrothiophene-indan-1,3-diones via a Squaramide-Catalyzed Sulfa-Michael/Aldol Domino Reaction
2016
Synthesis 48(08), 1131-1138(2016). doi:10.1055/s-0035-1560412
Asymmetric Synthesis of Functionalized Tricyclic Chromanes via an Organocatalytic Triple Domino Reaction
2017
A highly stereoselective triple domino reaction for the synthesis of functionalized tricyclic chromane scaffolds has been developed. A secondary amine-catalyzed domino Michael/Michael/aldol condensation reaction between aliphatic aldehydes, nitro-chromenes, and α,β-unsaturated aldehydes leads to the formation of synthetically important tricyclic chromanes bearing four contiguous stereogenic centers including a tetrasubstituted carbon in good yields (20–66%) and excellent stereoselectivities (>20:1 dr and >99% ee).
Organocatalytic Enantioselective Vinylogous Henry Reaction of 3,5-Dimethyl-4-nitroisoxazole with Trifluoromethyl Ketones
2017
The enantioselective vinylogous Henry reaction of 3,5-dimethyl-4-nitroisoxazole with trifluoromethyl ketones employing a bifunctional squaramide organocatalyst has been developed. A series of isoxazole bearing trifluoromethyl-substituted tertiary alcohols, 2-substituted (R)-1,1,1-trifluoro-3-(3-methyl-4-nitroisoxazol-5-yl)propan-2-ols, were obtained under these mild reaction conditions in good yields and moderate to good enantioselectivities
Enantioselective synthesis of pyrazolone α-aminonitrile derivatives via an organocatalytic Strecker reaction
2017
A new organocatalytic enantioselective Strecker reaction of pyrazolone-derived ketimine electrophiles has been developed. Using pseudo-enantiomeric squaramide catalysts the nucleophilic 1,2-addition of trimethylsilyl cyanide to the ketimines efficiently provides a direct entry to both enantiomers of pyrazolone α- aminonitrile derivatives at will in good yields and high enantioselectivities for a wide variety of substrates. peerReviewed
Organocatalytic Asymmetric Synthesis of Trifluoromethylated Tetrahydrocarbazoles by a Vinylogous Michael/Aldol Formal [4+2] Annulation
2018
Squaramide-Catalyzed Asymmetric aza-Friedel-Crafts/N,O-Acetalization Domino Reactions Between 2-Naphthols and Pyrazolinone Ketimines
2017
N-Boc ketimines derived from pyrazolin-5-ones were explored to develop an unprecedented domino aza-Friedel-Crafts/N,O-acetalization reaction with 2-naphthols. The novel method requires a catalyst loading of only 0.5 mol % of a bifunctional squaramide catalyst, is scalable to gram amounts, and provides a new series of furanonaphthopyrazolidinone derivatives bearing two vicinal tetra-substituted stereogenic centers in excellent yields (95-98 %) and stereoselectivity (>99:1 d.r. and 97-98 % ee). A different reactivity was observed in the case of 1-naphthols and other electron-rich phenols, which led to the aza-Friedel-Crafts adducts in 70-98 % yield and 47-98 % ee.
Asymmetric Synthesis of Tetrahydrobenzofurans and Annulated Dihydropyrans via Cooperative One-Pot Organo- and Silver-Catalysis
2016
Synthesis : journal of synthetic organic chemistry 48(19), 3207-3216(2016). doi:10.1055/s-0035-1561468
Organocatalytic Oxa-Michael/Michael/Michael/Aldol Condensation Quadruple Domino Sequence : Asymmetric Synthesis of Tricyclic Chromanes
2018
An efficient and highly stereoselective one-pot, four-component synthesis of functionalized tricyclic chromanes has been achieved through an organocatalyzed quadruple domino reaction. The reaction sequence involves an oxa-Michael/Michael/Michael/aldol condensation between alcohols, 2 equiv of acrolein, and nitrochromenes to generate the pharmaceutically important tricyclic chromanes bearing three contiguous stereogenic centers including a chiral tetrasubstituted carbon center in good domino yields (30–70%) and excellent diastereo- and enantioselectivities (>20:1 dr and >99% ee). peerReviewed
Enantioselective synthesis of 4H-pyranonaphthoquinones via sequential squaramide and silver catalysis
2015
Chemical communications 52(8), 1669-1672(2016). doi:10.1039/C5CC09592A
Asymmetric, Three-Component, One-Pot Synthesis of Spiropyrazolones and 2,5-Chromenediones from Aldol Condensation/NHC-Catalyzed Annulation Reactions
2016
A novel one-pot, three-component diastereo- and enantioselective synthesis of spiropyrazolones has been developed involving the aldol condensation of an enal to generate α,β-unsaturated pyrazolones, which react with a second equivalent of enal through an N-heterocyclic carbene (NHC)-catalyzed [3+2] annulation. The desired spirocyclopentane pyrazolones are obtained in moderate to good yields and good to excellent stereoselectivities. Alternatively, starting from cyclic 1,3-diketones, 2,5-chromenediones are available through [2+4] annulation.
N‐Heterocyclic Carbene Catalyzed [4+2] Annulation of Enals via a Double Vinylogous Michael Addition: Asymmetric Synthesis of 3,5‐Diaryl Cyclohexenones
2017
A strategy for the N-heterocyclic carbene (NHC) catalyzed asymmetric synthesis of 3,5-diaryl substituted cyclohexenones has been developed via oxidative [4+2] annulation of enals and alkenylisoxazoles. It is the first example of using NHC organocatalysis in a double vinylogous Michael type reaction, a challenging but highly desirable topic. This unprecedented protocol affords good yields as well as high to excellent diastereo- and enantioselectivities.
Asymmetric Synthesis of Amino-Bis-Pyrazolone Derivatives via an Organocatalytic Mannich Reaction.
2017
A new series of N-Boc ketimines derived from pyrazolin-5-ones have been used as electrophiles in asymmetric Mannich reactions with pyrazolones. The amino-bis-pyrazolone products are obtained in excellent yields and stereoselectivities by employing a very low loading of 1 mol % of a bifunctional squaramide organocatalyst. Depending on the substitution at position 4 of the pyrazolones, the new protocol allows for the generation of one or two tetrasubstituted stereocenters, including a one-pot version combing the Mannich reaction with a base-mediated halogenation. peerReviewed
CCDC 1516205: Experimental Crystal Structure Determination
2017
Related Article: Sun Lia, Lei Wang, Pankaj Chauhan, Anssi Peuronen, Kari Rissanen, Dieter Enders|2017|Synthesis|49|1808|doi:10.1055/s-0036-1588381
CCDC 1542055: Experimental Crystal Structure Determination
2017
Related Article: Suruchi Mahajan, Pankaj Chauhan, Uğur Kaya, Kristina Deckers, Kari Rissanen, Dieter Enders|2017|Chem.Commun.|53|6633|doi:10.1039/C7CC02874A
CCDC 1474771: Experimental Crystal Structure Determination
2016
Related Article: Uğur Kaya, Pankaj Chauhan, Kristina Deckers, Rakesh Puttreddy, Kari Rissanen, Gerhard Raabe, Dieter Enders|2016|Synthesis|48|3207|doi:10.1055/s-0035-1561468
CCDC 1474975: Experimental Crystal Structure Determination
2016
Related Article: Uğur Kaya, Pankaj Chauhan, Kristina Deckers, Rakesh Puttreddy, Kari Rissanen, Gerhard Raabe, Dieter Enders|2016|Synthesis|48|3207|doi:10.1055/s-0035-1561468
CCDC 1442230: Experimental Crystal Structure Determination
2016
Related Article: Lei Wang, Sun Li, Pankaj Chauhan, Daniel Hack,Arne R. Philipps, Rakesh Puttreddy, Kari Rissanen, Gerhard Raabe, Dieter Enders|2016|Chem.-Eur.J.|22|5123|doi:10.1002/chem.201600515
CCDC 1816580: Experimental Crystal Structure Determination
2018
Related Article: Mukesh Kumar, Pankaj Chauhan, Stephen J. Bailey, Ehsan Jafari, Carolina von Essen, Kari Rissanen, Dieter Enders|2018|Org.Lett.|20|1232|doi:10.1021/acs.orglett.8b00175
CCDC 1537523: Experimental Crystal Structure Determination
2017
Related Article: Pankaj Chauhan, Suruchi Mahajan, Uğur Kaya, Anssi Peuronen, Kari Rissanen, and Dieter Enders|2017|J.Org.Chem.|82|7050|doi:10.1021/acs.joc.7b01113
CCDC 1537522: Experimental Crystal Structure Determination
2017
Related Article: Pankaj Chauhan, Suruchi Mahajan, Uğur Kaya, Anssi Peuronen, Kari Rissanen, and Dieter Enders|2017|J.Org.Chem.|82|7050|doi:10.1021/acs.joc.7b01113
CCDC 1446165: Experimental Crystal Structure Determination
2016
Related Article: Lei Wang, Sun Li, Pankaj Chauhan, Daniel Hack,Arne R. Philipps, Rakesh Puttreddy, Kari Rissanen, Gerhard Raabe, Dieter Enders|2016|Chem.-Eur.J.|22|5123|doi:10.1002/chem.201600515
CCDC 1437740: Experimental Crystal Structure Determination
2016
Related Article: Suruchi Mahajan, Pankaj Chauhan, Marcus Blümel, Rakesh Puttreddy, Kari Rissanen, Gerhard Raabe, Dieter Enders|2016|Synthesis|48|1131|doi:10.1055/s-0035-1560412
CCDC 1476009: Experimental Crystal Structure Determination
2016
Related Article: Pankaj Chauhan, Suruchi Mahajan, Uğur Kaya, Arto Valkonen, Kari Rissanen and Dieter Enders|2016|Adv.Synth.Catal.|358|3173|doi:10.1002/adsc.201600554
CCDC 1437688: Experimental Crystal Structure Determination
2015
Related Article: Uğur Kaya, Pankaj Chauhan, Daniel Hack, Kristina Deckers, Rakesh Puttreddy, Kari Rissanen, Dieter Enders|2016|Chem.Commun.|52|1669|doi:10.1039/C5CC09592A
CCDC 1589299: Experimental Crystal Structure Determination
2018
Related Article: Ehsan Jafari, Pankaj Chauhan, Mukesh Kumar, Xiang-Yu Chen, Sun Li, Carolina von Essen, Kari Rissanen, Dieter Enders|2018|Eur.J.Org.Chem.|2018|2462|doi:10.1002/ejoc.201800034
CCDC 1572983: Experimental Crystal Structure Determination
2017
Related Article: Uğur Kaya, Pankaj Chauhan, Suruchi Mahajan, Kristina Deckers, Arto Valkonen, Kari Rissanen, Dieter Enders|2017|Angew.Chem.,Int.Ed.|56|15358|doi:10.1002/anie.201709224
CCDC 1534754: Experimental Crystal Structure Determination
2017
Related Article: Xiang-Yu Chen, Qiang Liu, Pankaj Chauhan, Sun Li, Anssi Peuronen, Kari Rissanen, Ehsan Jafari, Dieter Enders|2017|Angew.Chem.,Int.Ed.|56|6241|doi:10.1002/anie.201702881
CCDC 1542995: Experimental Crystal Structure Determination
2017
Related Article: Mukesh Kumar, Pankaj Chauhan, Arto Valkonen, Kari Rissanen, and Dieter Enders|2017|Org.Lett.|19|3025|doi:10.1021/acs.orglett.7b01322