Jon T. Njardarson

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Name: Njardarson, Jon
Organization: University of Arizona , USA
Department: Department of Chemistry and Biochemistry
Title: Associate(PhD)

TOPICS

Co-reporter:Isaac Chogii, Pradipta Das, Jason S. Fell, Kevin A. Scott, Mark N. Crawford, K. N. Houk, and Jon T. Njardarson
Journal of the American Chemical Society September 20, 2017 Volume 139(Issue 37) pp:13141-13141
Publication Date(Web):September 8, 2017
DOI:10.1021/jacs.7b07319
We report useful new lithium-assisted asymmetric anion-accelerated amino-Cope rearrangement cascades. A strategic nitrogen atom chiral auxiliary serves three critical roles, by (1) enabling in situ assembly of the chiral 3-amino-1,5-diene precursor, (2) facilitating the rearrangement via a lithium enolate chelate, and (3) imparting its influence on consecutive inter- or intramolecular C–C or C–X bond-forming events via resulting chiral enamide intermediates or imine products. The mechanism of the amino-Cope rearrangement was explored with density functional theory. A stepwise dissociation–recombination mechanism was found to be favored. The stereochemistry of the chiral auxiliary determines the stereochemistry of the Cope product by influencing the orientation of the lithium dienolate and sulfinylimine fragments in the recombination step. These robust asymmetric anion-accelerated amino-Cope enabled cascades open the door for rapid and predictable assembly of complex chiral acyclic and cyclic nitrogen-containing motifs in one pot.
Co-reporter:Edon Vitaku;David T. Smith ;Dr. Jon T. Njardarson
Angewandte Chemie 2016 Volume 128( Issue 6) pp:2283-2287
Publication Date(Web):
DOI:10.1002/ange.201511149

Abstract

Nitrogen heterocycles are found in a majority of approved small-molecule pharmaceuticals, and the number of approved fluorinated drugs is increasing each decade. Therefore, new approaches for accessing fluorinated nitrogen heterocycles are of great significance. A novel, scalable, and metal-free method for accessing a wide range of fluorinated indoles is described. This oxidative-dearomatization-enabled approach assembles 2-trifluoromethyl NH-indole products from simple commercially available anilines with hexafluoroacetylacetone in the presence of an organic oxidant. The nature of the aniline N-capping group is critical for the success of this new reaction. Furthermore, the indole products contain a 3-trifluoroacetyl group, which can be exploited to access a plethora of useful functional groups.

Co-reporter:Edon Vitaku;David T. Smith ;Dr. Jon T. Njardarson
Angewandte Chemie International Edition 2016 Volume 55( Issue 6) pp:2243-2247
Publication Date(Web):
DOI:10.1002/anie.201511149

Abstract

Nitrogen heterocycles are found in a majority of approved small-molecule pharmaceuticals, and the number of approved fluorinated drugs is increasing each decade. Therefore, new approaches for accessing fluorinated nitrogen heterocycles are of great significance. A novel, scalable, and metal-free method for accessing a wide range of fluorinated indoles is described. This oxidative-dearomatization-enabled approach assembles 2-trifluoromethyl NH-indole products from simple commercially available anilines with hexafluoroacetylacetone in the presence of an organic oxidant. The nature of the aniline N-capping group is critical for the success of this new reaction. Furthermore, the indole products contain a 3-trifluoroacetyl group, which can be exploited to access a plethora of useful functional groups.

Co-reporter:Pradipta Das and Jon T. Njardarson
Organic Letters 2015 Volume 17(Issue 16) pp:4030-4033
Publication Date(Web):August 6, 2015
DOI:10.1021/acs.orglett.5b01937
Two new approaches for forming 1,2,3,6-tetrahydropyridines are reported. Both reactions employ a strategic phosphate substituent on the nitrogen atom. In the presence of an additional phosphate substituent (X = P = O(OEt)2) an anionic cascade can by triggered upon treatment with base. Alternatively, when X = H the same 1,2,3,6-tetrahydropyridine product can be accessed via an acid catalyzed cyclization.
Co-reporter:Isaac Chogii ;Dr. Jon T. Njardarson
Angewandte Chemie International Edition 2015 Volume 54( Issue 46) pp:13706-13710
Publication Date(Web):
DOI:10.1002/anie.201506559

Abstract

An asymmetric [3+2] annulation reaction to form 3-pyrroline products is reported. Upon treatment with lithium diisopropylamide, readily available ethyl 4-bromocrotonate is deprotonated and trapped with Ellman imines selectively at the α-position to yield enantiopure 3-pyrroline products. This new method is compatible with aryl, alkyl, and vinyl imines. The efficacy of the method is showcased by short asymmetric total syntheses of (−)-supinidine, (−)-isoretronecanol, and (+)-elacomine. This novel annulation approach also works for an aldehyde, thus providing access to a 2,5-dihydrofuran product in a single step from simple precursors. By modifying the structure of the carbanion nucleophile, an asymmetric vinylogous aza-Darzens reaction can be realized.

Co-reporter:Isaac Chogii ;Dr. Jon T. Njardarson
Angewandte Chemie 2015 Volume 127( Issue 46) pp:13910-13914
Publication Date(Web):
DOI:10.1002/ange.201506559

Abstract

An asymmetric [3+2] annulation reaction to form 3-pyrroline products is reported. Upon treatment with lithium diisopropylamide, readily available ethyl 4-bromocrotonate is deprotonated and trapped with Ellman imines selectively at the α-position to yield enantiopure 3-pyrroline products. This new method is compatible with aryl, alkyl, and vinyl imines. The efficacy of the method is showcased by short asymmetric total syntheses of (−)-supinidine, (−)-isoretronecanol, and (+)-elacomine. This novel annulation approach also works for an aldehyde, thus providing access to a 2,5-dihydrofuran product in a single step from simple precursors. By modifying the structure of the carbanion nucleophile, an asymmetric vinylogous aza-Darzens reaction can be realized.

Co-reporter:Brandon R. Smith ; Candice M. Eastman
Journal of Medicinal Chemistry 2014 Volume 57(Issue 23) pp:9764-9773
Publication Date(Web):September 25, 2014
DOI:10.1021/jm501105n
The diversity of elements among U.S. Food and Drug Administration (FDA) approved pharmaceuticals is analyzed and reported, with a focus on atoms other than carbon, hydrogen, oxygen, and nitrogen. Our analysis reveals that sulfur, chlorine, fluorine, and phosphorous represent about 90% of elemental substitutions, with sulfur being the fifth most used element followed closely by chlorine, then fluorine and finally phosphorous in the eighth place. The remaining 10% of substitutions are represented by 16 other elements of which bromine, iodine, and iron occur most frequently. The most detailed parts of our analysis are focused on chlorinated drugs as a function of approval date, disease condition, chlorine attachment, and structure. To better aid our chlorine drug analyses, a new poster showcasing the structures of chlorinated pharmaceuticals was created specifically for this study. Phosphorus, bromine, and iodine containing drugs are analyzed closely as well, followed by a discussion about other elements.
Co-reporter:Edon Vitaku ; David T. Smith
Journal of Medicinal Chemistry 2014 Volume 57(Issue 24) pp:10257-10274
Publication Date(Web):September 25, 2014
DOI:10.1021/jm501100b
Nitrogen heterocycles are among the most significant structural components of pharmaceuticals. Analysis of our database of U.S. FDA approved drugs reveals that 59% of unique small-molecule drugs contain a nitrogen heterocycle. In this review we report on the top 25 most commonly utilized nitrogen heterocycles found in pharmaceuticals. The main part of our analysis is divided into seven sections: (1) three- and four-membered heterocycles, (2) five-, (3) six-, and (4) seven- and eight-membered heterocycles, as well as (5) fused, (6) bridged bicyclic, and (7) macrocyclic nitrogen heterocycles. Each section reveals the top nitrogen heterocyclic structures and their relative impact for that ring type. For the most commonly used nitrogen heterocycles, we report detailed substitution patterns, highlight common architectural cores, and discuss unusual or rare structures.
Co-reporter:Elizabeth A. Ilardi ; Edon Vitaku
Journal of Medicinal Chemistry 2014 Volume 57(Issue 7) pp:2832-2842
Publication Date(Web):October 8, 2013
DOI:10.1021/jm401375q
Among carbon, hydrogen, oxygen, and nitrogen, sulfur and fluorine are both leading constituents of the pharmaceuticals that comprise our medicinal history. In efforts to stimulate the minds of both the general public and expert scientist, statistics were collected from the trends associated with therapeutics spanning 12 disease categories (a total of 1969 drugs) from our new graphical montage compilation: disease focused pharmaceuticals posters. Each poster is a vibrant display of a collection of pharmaceuticals (including structural image, Food and Drug Administration (FDA) approval date, international nonproprietary name (INN), initial market name, and a color-coded subclass of function) organized chronologically and classified according to an association with a particular clinical indication. Specifically, the evolution and structural diversity of sulfur and the popular integration of fluorine into drugs introduced over the past 50 years are evaluated. The presented qualitative conclusions in this article aim to promote innovative insights into drug development.
Co-reporter:Qingliang Yang, Cristian Draghici, Jon T. Njardarson, Fang Li, Brandon R. Smith and Pradipta Das  
Organic & Biomolecular Chemistry 2014 vol. 12(Issue 2) pp:330-344
Publication Date(Web):21 Nov 2013
DOI:10.1039/C3OB42191K
The evolution of the synthetic strategy resulting in a total synthesis of vinigrol is presented. Oxidative dearomatization/intramolecular Diels–Alder cycloaddition has served as the successful cornerstone for all of the approaches. Extensive radical cyclization efforts to form the tetracyclic core resulted in interesting and surprising reaction outcomes, none of which could be advanced to vinigrol. These cyclization obstacles were successfully overcome by using Heck instead of radical cyclizations. The total synthesis features a trifluoroethyl ether protecting group being used for the first time in organic synthesis. The logic of its selection and the group's importance beyond protecting the C8a hydroxyl group is presented along with a discussion of strategies for its removal. Because of the compact tetracyclic cage the route is built around many unusual reaction observations and solutions have emerged. For example, a first of its kind Grob fragmentation reaction featuring a trifluoroethyl leaving group has been uncovered, interesting interrupted selenium dioxide allylic oxidations have been observed as well as intriguing catalyst and counterion dependent directed hydrogenations.
Co-reporter:Boying Guo, Edon Vitaku, Jon T. Njardarson
Tetrahedron Letters 2014 Volume 55(Issue 21) pp:3232-3234
Publication Date(Web):21 May 2014
DOI:10.1016/j.tetlet.2014.04.028
Presented in this Letter is a mild new method to stereoselectively ring open 1,1-disubstituted vinyl oxiranes using dialkyl dithiophosphate nucleophiles. This new reaction proceeds in toluene at room temperature to afford tri- and tetrasubstituted allylic alcohols with high Z-selectivity. The syn relationship between the alcohol and the newly incorporated dithiophosphate moiety presented an opportunity to evaluate the anionic hopping properties of the ring opening product. Treatment of the ring opening product with base results in a facile phosphate hopping followed by a selective thiolate 3-exo-trig instead of a 5-exo-tet cyclization.
Co-reporter:David T. Smith ; Jon T. Njardarson
Angewandte Chemie International Edition 2014 Volume 53( Issue 17) pp:4278-4280
Publication Date(Web):
DOI:10.1002/anie.201400502
Co-reporter:David T. Smith ; Jon T. Njardarson
Angewandte Chemie 2014 Volume 126( Issue 17) pp:4364-4366
Publication Date(Web):
DOI:10.1002/ange.201400502
Co-reporter:Daniel J. Mack and Jon T. Njardarson
ACS Catalysis 2013 Volume 3(Issue 2) pp:272
Publication Date(Web):January 14, 2013
DOI:10.1021/cs300771d
New catalytic ring-expansion reactions of strained ring (hetero- and carbocyclic) substrates reported in the last six years (2006–2012) are presented. As evident from the diversity of new approaches, this is a vibrant area of research. Metals ranging from magnesium to gold have been used as catalysts. Some of these reactions allow access to enantioenriched products by employing catalysts decorated with chiral organic motifs (primarily C-2 symmetric).Keywords: catalysis; cyclobutane; cyclopropane; heterocycles; ring expansion; strained rings
Co-reporter:B. Guo and J. T. Njardarson  
Chemical Communications 2013 vol. 49(Issue 92) pp:10802-10804
Publication Date(Web):14 Oct 2013
DOI:10.1039/C3CC46660D
Dialkyl dithiophosphates selectively ring open vinyl oxetanes in excellent yields under mild reaction conditions to form useful allylic thiophosphate products with high Z-selectivity.
Co-reporter:Qingliang Yang, Jon T. Njardarson
Tetrahedron Letters 2013 Volume 54(Issue 51) pp:7080-7082
Publication Date(Web):18 December 2013
DOI:10.1016/j.tetlet.2013.10.097
A trifluoroethyl (TFE) ether is specifically introduced as a protecting group in organic chemistry. Its first strategic application and removal in the total synthesis of vinigrol is discussed. Two lithium base mediated deprotection strategies for its removal are presented in this Letter. In one deprotection approach, the trifluoroethyl ether is converted to a difluorovinyl ether and then catalytically cleaved using osmium tetraoxide, while in the second approach a difluorovinyl anion is formed and trapped with an electrophilic oxygen reagent (MoOPH) to form a labile difluoroacetate. To further aid the reader, a summary of approaches for forming trifluoroethyl ethers is included as well as a discussion of alternate deprotection strategies.
Co-reporter:Elizabeth A. Ilardi, Edon Vitaku, and Jon T. Njardarson
Journal of Chemical Education 2013 Volume 90(Issue 10) pp:1403-1405
Publication Date(Web):September 13, 2013
DOI:10.1021/ed4002317
Disease Focused Posters is a new, free, and readily accessible collection of graphical timelines that arrange the vast number of FDA approved pharmaceuticals according to a specific theme. Capitalizing on the elegance of structural imagery and the innovative functions of organic compounds, each poster (in its simplistic appearance) has the capacity to communicate a wealth of information that appeals to the educational desires of the public, from the non-scientist to the expert.Keywords: Applications of Chemistry; Continuing Education; Drugs/Pharmaceuticals; General Public; Graduate Education/Research; Inquiry-Based/Discovery Learning; Internet/Web-Based Learning; Natural Products; Organic Chemistry; Upper-Division Undergraduate;
Co-reporter:Elizabeth A. Ilardi and Jon T. Njardarson
The Journal of Organic Chemistry 2013 Volume 78(Issue 19) pp:9533-9540
Publication Date(Web):September 11, 2013
DOI:10.1021/jo401776s
Ring expansion reactions of strained vinylic heterocyclic substrates have attracted the attention of the synthetic community for decades. Strategic manipulations of these organic architectures enable access to many useful synthetic intermediates. This paper highlights various methods for the ring expansion of vinyloxiranes, -thiiranes, and -aziridines described in the literature from 1964 to 2013.
Co-reporter:Qingliang Yang; Jon T. Njardarson;Dr. Cristian Draghici;Dr. Fang Li
Angewandte Chemie International Edition 2013 Volume 52( Issue 33) pp:8648-8651
Publication Date(Web):
DOI:10.1002/anie.201304624
Co-reporter:Daniel J. Mack; Jon T. Njardarson
Angewandte Chemie International Edition 2013 Volume 52( Issue 5) pp:1543-1547
Publication Date(Web):
DOI:10.1002/anie.201208412
Co-reporter:Qingliang Yang; Jon T. Njardarson;Dr. Cristian Draghici;Dr. Fang Li
Angewandte Chemie 2013 Volume 125( Issue 33) pp:8810-8813
Publication Date(Web):
DOI:10.1002/ange.201304624
Co-reporter:Daniel J. Mack; Jon T. Njardarson
Angewandte Chemie 2013 Volume 125( Issue 5) pp:1583-1587
Publication Date(Web):
DOI:10.1002/ange.201208412
Co-reporter:Thomas J. L. Mustard ; Daniel J. Mack ; Jon T. Njardarson ;Paul Ha-Yeon Cheong
Journal of the American Chemical Society 2012 Volume 135(Issue 4) pp:1471-1475
Publication Date(Web):December 31, 2012
DOI:10.1021/ja310065z
Density functional theory computations of the Cu-catalyzed ring expansion of vinyloxiranes is mediated by a traceless dual Cu(I)-catalyst mechanism. Overall, the reaction involves a monomeric Cu(I)-catalyst, but a single key step, the Cu migration, requires two Cu(I)-catalysts for the transformation. This dual-Cu step is found to be a true double Cu(I) transition state rather than a single Cu(I) transition state in the presence of an adventitious, spectator Cu(I). Both Cu(I) catalysts are involved in the bond forming and breaking process. The single Cu(I) transition state is not a stationary point on the potential energy surface. Interestingly, the reductive elimination is rate-determining for the major diastereomeric product, while the Cu(I) migration step is rate-determining for the minor. Thus, while the reaction requires dual Cu(I) activation to proceed, kinetically, the presence of the dual-Cu(I) step is untraceable. The diastereospecificity of this reaction is controlled by the Cu migration step. Suprafacial migration is favored over antarafacial migration due to the distorted Cu π-allyl in the latter.
Co-reporter:Daniel J. Mack and Jon T. Njardarson  
Chemical Science 2012 vol. 3(Issue 11) pp:3321-3325
Publication Date(Web):31 Aug 2012
DOI:10.1039/C2SC21007J
We report how mechanistically inspired metal additive choices result in acceleration of the copper catalyzed vinyl aziridine ring expansion reaction. Most importantly, we demonstrate how the use of in situ reducing agents significantly accelerates the reaction, suggesting a copper(I) active species. These acceleration results were confirmed using Cu(hfacac)(cod) as catalyst. NMR kinetic studies revealed the relative importance of olefin and sulfonamide electronics on the reaction rate and established the order of both catalyst and substrate, which together favored a new copper(I) insertion mechanism.
Co-reporter:Daniel J. Mack, Lindsay A. Batory, and Jon T. Njardarson
Organic Letters 2012 Volume 14(Issue 1) pp:378-381
Publication Date(Web):December 21, 2011
DOI:10.1021/ol203129d
Detailed in this account are our efforts toward efficient oxacycle syntheses. Two complementary approaches are discussed, with both employing chemoselective allyl ether activation and rearrangement as the key step. Vinyl substituted oxiranes and oxetanes provide a single step access to dihydropyrans and tetrahydrooxepines. Oxiranes proved to be poor substrates, while oxetanes were slightly better. An alternative approach using substituted allyl ethers proved successful and addressed the limitations encountered in the ring expansions.
Co-reporter:Daniel J. Mack, Boying Guo and Jon T. Njardarson  
Chemical Communications 2012 vol. 48(Issue 63) pp:7844-7846
Publication Date(Web):02 Jul 2012
DOI:10.1039/C2CC33551D
Unsaturated cyclic ethers can be mildly and selectively reduced with catalytic amounts of B(C6F5)3 in the presence of an alkylsilane. The allylic position is preferentially reduced with minimal or no scrambling of olefin geometry. For electronically equivalent substrates, steric factors guide the reducing agent to the least substituted site.
Co-reporter:Daniel J. Mack, Jun Isoe, Roger L. Miesfeld, Jon T. Njardarson
Bioorganic & Medicinal Chemistry Letters 2012 Volume 22(Issue 16) pp:5177-5181
Publication Date(Web):15 August 2012
DOI:10.1016/j.bmcl.2012.06.076
A collection of Golgicide A (GCA) analogs has been synthesized and evaluated in larval and adult mosquito assays. Commercially available GCA is a mixture of four compounds. One enantiomer (GCA-2) of the major diastereomer in this mixture was shown to be responsible for the unique activity of GCA. Structure–activity studies (SAR) of the GCA architecture suggested that the pyridine ring was most easily manipulated without loss or gain in new activity. Eighteen GCA analogs were synthesized of which five displayed distinct behavior between larval and adult mosquitos, resulting in complete mortality of both Aedes aegypti and Anopheles stephensi larvae. Two analogs from the collection were shown to be distinct from the rest in displaying high selectivity and efficiency in killing An. stephensi larvae.
Co-reporter:Cristian Draghici and Jon T. Njardarson
Journal of Chemical Education 2012 Volume 89(Issue 8) pp:1080-1082
Publication Date(Web):May 23, 2012
DOI:10.1021/ed2006423
Chemistry By Design is a new educational Web site that contains a continuously growing database of natural product and pharmaceutical syntheses. It focuses on providing visitors with an opportunity to learn about the wonders of synthetic organic chemistry by browsing published sequences and viewing each synthetic step individually. Emphasis has been placed on exploiting the wonderful graphical language of organic chemistry to most effectively communicate the educational content as well as to allow visitors to test their knowledge in a variety of different ways. Chemistry By Design is also available as a free application for both Apple iOS and Android devices.Keywords: Computer-Based Learning; Drugs/Pharmaceuticals; General Public; Graduate Education/Research; Internet/Web-Based Learning; Organic Chemistry; Problem Solving/Decision Making; Synthesis; Upper-Division Undergraduate;
Co-reporter:Boying Guo;Gregg Schwarzwalder; Jon T. Njardarson
Angewandte Chemie 2012 Volume 124( Issue 23) pp:5773-5776
Publication Date(Web):
DOI:10.1002/ange.201201367
Co-reporter:Fang Li;David Calabrese;Matthew Brichacek;Ivy Lin; Jon T. Njardarson
Angewandte Chemie 2012 Volume 124( Issue 8) pp:1974-1977
Publication Date(Web):
DOI:10.1002/ange.201108261
Co-reporter:Boying Guo;Gregg Schwarzwalder; Jon T. Njardarson
Angewandte Chemie International Edition 2012 Volume 51( Issue 23) pp:5675-5678
Publication Date(Web):
DOI:10.1002/anie.201201367
Co-reporter:Fang Li;David Calabrese;Matthew Brichacek;Ivy Lin; Jon T. Njardarson
Angewandte Chemie International Edition 2012 Volume 51( Issue 8) pp:1938-1941
Publication Date(Web):
DOI:10.1002/anie.201108261
Co-reporter:Jon T. Njardarson
Tetrahedron 2011 67(40) pp: 7631-7666
Publication Date(Web):
DOI:10.1016/j.tet.2011.06.079
Co-reporter:Nicholas A. McGrath, Matthew Brichacek, and Jon T. Njardarson
Journal of Chemical Education 2010 Volume 87(Issue 12) pp:1348-1349
Publication Date(Web):October 1, 2010
DOI:10.1021/ed1003806
A new free graphical teaching tool that highlights the beautiful organic architectures of the top selling pharmaceuticals is detailed on two posters. In addition to the multitude of teaching and data-mining opportunities these posters offer, they were also created to emphasize the central role organic chemists play in the development of new therapeutics.Keywords (Audience): General Public; Upper-Division Undergraduate; Keywords (Domain): Organic Chemistry; Keywords (Pedagogy): Inquiry-Based/Discovery Learning; Keywords (Topic): Applications of Chemistry; Drugs/Pharmaceuticals; Natural Products; Keywords (descriptor): CLIC;
Co-reporter:B. Guo and J. T. Njardarson
Chemical Communications 2013 - vol. 49(Issue 92) pp:NaN10804-10804
Publication Date(Web):2013/10/14
DOI:10.1039/C3CC46660D
Dialkyl dithiophosphates selectively ring open vinyl oxetanes in excellent yields under mild reaction conditions to form useful allylic thiophosphate products with high Z-selectivity.
Co-reporter:Daniel J. Mack, Boying Guo and Jon T. Njardarson
Chemical Communications 2012 - vol. 48(Issue 63) pp:NaN7846-7846
Publication Date(Web):2012/07/02
DOI:10.1039/C2CC33551D
Unsaturated cyclic ethers can be mildly and selectively reduced with catalytic amounts of B(C6F5)3 in the presence of an alkylsilane. The allylic position is preferentially reduced with minimal or no scrambling of olefin geometry. For electronically equivalent substrates, steric factors guide the reducing agent to the least substituted site.
Co-reporter:Daniel J. Mack and Jon T. Njardarson
Chemical Science (2010-Present) 2012 - vol. 3(Issue 11) pp:NaN3325-3325
Publication Date(Web):2012/08/31
DOI:10.1039/C2SC21007J
We report how mechanistically inspired metal additive choices result in acceleration of the copper catalyzed vinyl aziridine ring expansion reaction. Most importantly, we demonstrate how the use of in situ reducing agents significantly accelerates the reaction, suggesting a copper(I) active species. These acceleration results were confirmed using Cu(hfacac)(cod) as catalyst. NMR kinetic studies revealed the relative importance of olefin and sulfonamide electronics on the reaction rate and established the order of both catalyst and substrate, which together favored a new copper(I) insertion mechanism.
Co-reporter:Qingliang Yang, Cristian Draghici, Jon T. Njardarson, Fang Li, Brandon R. Smith and Pradipta Das
Organic & Biomolecular Chemistry 2014 - vol. 12(Issue 2) pp:NaN344-344
Publication Date(Web):2013/11/21
DOI:10.1039/C3OB42191K
The evolution of the synthetic strategy resulting in a total synthesis of vinigrol is presented. Oxidative dearomatization/intramolecular Diels–Alder cycloaddition has served as the successful cornerstone for all of the approaches. Extensive radical cyclization efforts to form the tetracyclic core resulted in interesting and surprising reaction outcomes, none of which could be advanced to vinigrol. These cyclization obstacles were successfully overcome by using Heck instead of radical cyclizations. The total synthesis features a trifluoroethyl ether protecting group being used for the first time in organic synthesis. The logic of its selection and the group's importance beyond protecting the C8a hydroxyl group is presented along with a discussion of strategies for its removal. Because of the compact tetracyclic cage the route is built around many unusual reaction observations and solutions have emerged. For example, a first of its kind Grob fragmentation reaction featuring a trifluoroethyl leaving group has been uncovered, interesting interrupted selenium dioxide allylic oxidations have been observed as well as intriguing catalyst and counterion dependent directed hydrogenations.
(S,E)-N-(2-((tert-Butyldimethylsilyl)oxy)ethylidene)-2-methylpropane-2-sulfinamide
7-Benzofuranol, 2,3-dihydro-
Carbamic acid, [4-(phenylmethoxy)phenyl]-, 1,1-dimethylethyl ester
Carbamic acid, (4-methoxyphenyl)-, 9H-fluoren-9-ylmethyl ester
TERT-BUTYL N-(2,4-DIMETHOXYPHENYL)CARBAMATE