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https://www.readbyqxmd.com/read/29755145/remote-c-h-functionalization-via-selective-hydrogen-atom-transfer
#1
Leah M Stateman, Kohki M Nakafuku, David A Nagib
The selective functionalization of remote C-H bonds via intramolecular hydrogen atom transfer (HAT) is transformative for organic synthesis. This radical-mediated strategy provides access to novel reactivity that is complementary to closed-shell pathways. As modern methods for mild generation of radicals are continually developed, inherent selectivity paradigms of HAT mechanisms offer unparalleled opportunities for developing new strategies for C-H functionalization. This review outlines the history, recent advances, and mechanistic underpinnings of intramolecular HAT as a guide to addressing ongoing challenges in this arena...
April 2018: Synthesis
https://www.readbyqxmd.com/read/29662252/scalable-synthesis-of-hydrido-disiloxanes-from-silanes-a-one-pot-preparation-of-1-3-diphenyldisiloxane-from-phenylsilane
#2
Joseph A Buonomo, Carter G Eiden, Courtney C Aldrich
A simple, one-pot, and high-yielding synthesis of 1,3-diphenyldisiloxane is presented. The preparation of similar symmetrical disiloxane materials is also accomplished with this same protocol. This mechano-chemical procedure is efficient and highly scalable, furnishing a convenient route to hydrido-disiloxanes from widely accessible commercially available silanes.
January 2018: Synthesis
https://www.readbyqxmd.com/read/29568140/a-general-protocol-for-radical-anion-3-2-cycloaddition-enabled-by-tandem-lewis-acid-photoredox-catalysis
#3
Adrian G Amador, Evan M Sherbrook, Zhan Lu, Tehshik P Yoon
We report herein a method for intermolecular [3 + 2] cycloaddition between aryl cyclopropyl ketones and alkenes involving the combination of Lewis acid and photoredox catalysis. In contrast to other more common methods for [3 + 2] cycloaddition, these conditions operate using a broad range of both electron-rich and electron-deficient reaction partners. The critical factors predicting the success of these reactions is the redox potential of the cyclopropyl ketone and the ability of the alkene to stabilize a key radical intermediate...
2018: Synthesis
https://www.readbyqxmd.com/read/29507449/1-3-4-oxadiazole-and-heteroaromatic-fused-1-2-4-triazole-synthesis-using-diverted-umpolung-amide-synthesis
#4
Kazuyuki Tokumaru, Kalisankar Bera, Jeffrey N Johnston
Umpolung Amide Synthesis (UmAS) has emerged as a superior alternative to conventional amide synthesis methods based on carbonyl electrophiles in a range of situations, particularly when epimerization-prone couplings are prescribed. In an unanticipated development during our most recent studies, it was discovered that diacyl hydrazide products from UmAS were not formed as intermediates when using an acyl hydrazide as the amine acceptor. This resulted in a new preparation of 1,3,4-oxadiazoles from α-bromonitroalkane donors...
October 2017: Synthesis
https://www.readbyqxmd.com/read/28690345/n-heterocyclic-carbene-and-chiral-br%C3%A3-nsted-acid-cooperative-catalysis-for-a-highly-enantioselective-4-2-annulation
#5
Dian-Feng Chen, Tomislav Rovis
A chiral NHC/Brønsted acid cooperative catalysis system has been developed for asymmetric annulation of functionalized benzaldehydes and activated ketones through dearomative generation of dienolate.
January 2017: Synthesis
https://www.readbyqxmd.com/read/28090124/practical-synthetic-procedures-for-the-iron-catalyzed-intermolecular-olefin-aminohydroxylation-using-functionalized-hydroxylamines
#6
Cheng-Liang Zhu, Deng-Fu Lu, Jeffrey D Sears, Zhen-Xin Jia, Hao Xu
A set of practical synthetic procedures for the iron-catalyzed intermolecular olefin aminohydroxylation reactions in gram scale is reported. In these transformations, a bench-stable functionalized hydroxylamine is applied as the amination reagent. This method is compatible with a broad range of synthetically valuable olefins including those that are incompatible with the existing aminohydroxylation methods. It also provides valuable amino alcohol building blocks with regio- and stereo-chemical arrays that are complementary to known methods...
September 2016: Synthesis
https://www.readbyqxmd.com/read/28890578/detrifluoroacetylative-generation-of-halogenated-enolates-practical-access-to-perhalogenated-ketones-and-alkenes
#7
Kaluvu Balaraman, Max Moskowitz, Yang Liu, Christian Wolf
Sequential chlorination/fluorination of aromatic trifluoroacetylated ketones gives 1-aryl 2-chloro-2,4,4,4-tetrafluoro-butan-1,3-dione hydrates that are used for the synthesis of ketones and alkenes exhibiting a terminal bromochlorofluoromethyl group. The hydrates undergo detrifluoroacetylative cleavage and subsequent bromination in the presence of a copper(II)bisoxazoline catalyst, K2CO3 and NBS at room temperature. The corresponding bromochlorofluoromethyl ketones can be applied in Wittig and Horner-Wadsworth-Emmons reactions and dibromoalkenylations...
August 2016: Synthesis
https://www.readbyqxmd.com/read/27681860/asymmetric-synthesis-of-dipropionate-derivatives-through-catalytic-hydrogenation-of-enantioenriched-e-ketene-heterodimers
#8
Shi Chen, Mukulesh Mondal, Ahmad A Ibrahim, Kraig A Wheeler, Nessan J Kerrigan
A highly diastereoselective approach to dipropionate derivatives through Pd/C-catalyzed hydrogenation of enantioenriched E-ketene heterodimers is described. Catalytic hydrogenation of the E-isomer of ketene heterodimer β-lactones (12 examples) provides access to syn,anti-β-lactones (dipropionate derivatives) bearing up to three stereogenic centers (dr up to 49:1), and with excellent transfer of chirality (ee up to >99%).
August 2016: Synthesis
https://www.readbyqxmd.com/read/27482123/improved-synthesis-of-mdl-73811-a-potent-adometdc-inhibitor-and-anti-trypanosomal-compound
#9
Anthony J Brockway, Casey C Cosner, Oleg A Volkov, Margaret A Phillips, Jef K De Brabander
An improved synthesis of MDL 73811 - a potent AdoMetDC (S-adenosylmethionine decarboxylease) inhibitor and anti-trypanosomal compound with in vivo activity has been completed in four steps from commercially available 2',3'-O-isopropylideneadenosine. Utilization of Mitsunobu chemistry was crucial for the reliable and scalable introduction of the 5'-methylamine moiety, which was problematic using traditional activation/displacement chemistry as previously reported. All reactions in this synthesis were run on gram-scale resulting in a five-fold increase in yield over the original synthesis...
July 2016: Synthesis
https://www.readbyqxmd.com/read/27413246/synthesis-of-5-hydroxymethylcytidine-and-5-hydroxymethyl-uridine-modified-rna
#10
Christian Riml, Ronald Micura
We report on the syntheses of 5-hydroxymethyl-uridine [5hm(rU)] and -cytidine [5hm(rC)] phosphoramidites and their incorporation into RNA by solid-phase synthesis. Deprotection of the oligonucleotides is accomplished in a straightforward manner using standard conditions, confirming the appropriateness of the acetyl protection used for the pseudobenzylic alcohol moieties. The approach provides robust access to 5hm(rC/U)-modified RNAs that await applications in pull-down experiments to identify potential modification enzymes...
April 2016: Synthesis
https://www.readbyqxmd.com/read/27152053/acetoxy-substituted-cyclopropane-dicarbonyls-as-stable-donor-acceptor-acceptor-cyclopropanes
#11
Yahaira Reyes, Keith T Mead
A study of cyclopropanations of oxy-substituted ethenes with ethyl α-diazoaroyl acetates is described. Whereas trimethylsilyl vinyl ether and ethyl vinyl ether gave dihydrofuran products, stable cyclopropanes were isolated when vinyl acetate was used. Yields ranged from 0-87%, depending on the nature and position of the aryl ring substituent.
October 2015: Synthesis
https://www.readbyqxmd.com/read/26806984/iron-catalyzed-diastereoselective-intramolecular-olefin-aminobromination-with-bromide-ion
#12
Jun-Shan Tian, Cheng-Liang Zhu, Yun-Rong Chen, Hao Xu
A new iron-catalyzed diastereoselective aminobromination method is reported for both internal and terminal olefins (yield up to 90% and dr up to >20:1). In this transformation, a functionalized hydroxylamine and bromide ion were used as the nitrogen and bromine source, respectively. This method is compatible with a broad range of olefins and provides a convenient approach to synthetically valuable vicinal bromo primary amines. Our studies suggest that both the diastereoselectivity and enantioselectivity for the olefin aminobromination can be controlled by iron catalysts...
June 2015: Synthesis
https://www.readbyqxmd.com/read/26568642/synthesis-of-a-series-of-novel-3-9-disubstituted-phenanthrenes-as-analogues-of-known-nmda-receptor-allosteric-modulators
#13
Mark W Irvine, Guangyu Fang, Richard Eaves, Maria B Mayo-Martin, Erica S Burnell, Blaise M Costa, Georgia R Culley, Arturas Volianskis, Graham L Collingridge, Daniel T Monaghan, David E Jane
9-Substituted phenanthrene-3-carboxylic acids have been reported to have allosteric modulatory activity at the NMDA receptor. This receptor is activated by the excitatory neurotransmitter L-glutamate and has been implicated in a range of neurological disorders such as schizophrenia, epilepsy and chronic pain and neurodegenerative disorders such as Alzheimer's disease. Herein, the convenient synthesis of a wide range of novel 3,9-disubstituted phenanthrene derivatives starting from a few common intermediates is described...
June 1, 2015: Synthesis
https://www.readbyqxmd.com/read/26508806/rhodium-catalyzed-intermolecular-5-1-and-5-2-cycloadditions-using-1-4-enynes-with-an-electron-donating-ester-on-the-3-position
#14
Casi M Schienebeck, Wangze Song, Angela M Smits, Weiping Tang
Various 3-acyloxy-1,4-enynes could be employed in rhodium-catalyzed intermolecular [5+1] and [5+2] cycloadditions with CO or alkynes, respectively. The rate of these cycloadditions could be accelerated significantly by using 1,4-enynes with an electron-donating ester on the 3-position. The scope of rhodium-catalyzed [5+1] and [5+2] cycloadditions were examined by using 1,4-enynes bearing an electron-donating ester.
May 2015: Synthesis
https://www.readbyqxmd.com/read/26752794/an-asymmetric-organocatalytic-quadruple-domino-reaction-employing-a-vinylogous-friedel-crafts-michael-michael-aldol-condensation-sequence
#15
Arne R Philipps, Lars Fritze, Nico Erdmann, Dieter Enders
An organocatalytic quadruple cascade initiated by a Friedel-Crafts-type reaction is described. The (S)-diphenylprolinol trimethylsilyl ether catalyzed reaction yields highly functionalized cyclohexenecarbaldehydes bearing a 1,1-bis[4-(dialkylamino)phenyl]ethene moiety and three contiguous stereogenic centers. The reaction tolerates various functional groups and all products are obtained with very good diastereoselectivity and with virtually complete enantiomeric excess.
April 2, 2015: Synthesis
https://www.readbyqxmd.com/read/27003951/efficient-syntheses-of-vitamin-k-chain-shortened-acid-metabolites
#16
Aaron M Teitelbaum, Michele Scian, Wendel L Nelson, Allan E Rettie
Vitamin K sequentially undergoes ω-oxidation followed by successive rounds of β-oxidation to ultimately produce two chain-shortened carboxylic acid metabolites, vitamin K acid 1 and vitamin K acid 2. Two facile syntheses of these acid metabolites are described, each starting from commercially available menadione-cyclopentadiene adduct 3. Vitamin K acid 1 was synthesized in five steps via alkylation with a geranyl halide followed by subsequent oxidation reactions, while fully retaining the trans configuration of the side chain 2',3'-double bond...
April 2015: Synthesis
https://www.readbyqxmd.com/read/26722133/organocatalytic-asymmetric-domino-michael-henry-reaction-of-indolin-3-ones-with-o-formyl-%C3%AE-nitrostyrenes
#17
Suruchi Mahajan, Pankaj Chauhan, Charles C J Loh, Server Uzungelis, Gerhard Raabe, Dieter Enders
A highly diastereo- and enantioselective domino Michael/Henry reaction of 1-acetylindolin-3-ones with o-formyl-(E)-β-nitrostyrenes catalyzed by low loading of a quinine-derived amine-squaramide provides the corresponding indolin-3-one derivatives bearing four adjacent stereogenic centers in good to high yields and with excellent stereoselectivities.
April 1, 2015: Synthesis
https://www.readbyqxmd.com/read/26722132/organocatalytic-asymmetric-synthesis-of-dihydroisoquinolinones-via-a-one-pot-aza-henry-hemiaminalization-oxidation-sequence
#18
Robert Hahn, Ehsan Jafari, Gerhard Raabe, Dieter Enders
The asymmetric organocatalytic one-pot synthesis of trans-3,4-disubstituted 3,4-dihydroisoquinolin-1(2H)-ones is described. Starting from 2-(nitromethyl)benzaldehydes and various N-protected aldimines, 5 mol% of a quinine-based squaramide organocatalyst was used to synthesize the title compounds as virtually single diastereomers via an aza-Henry-hemiaminalization-oxidation sequence. Moderate to good yields (39-78%) and moderate to very good enantioselectivities (40-95% ee) were reached.
February 1, 2015: Synthesis
https://www.readbyqxmd.com/read/28250502/effect-of-substituents-and-stability-of-transient-aluminum-aminals-in-the-presence-of-nucleophiles
#19
Francis J Barrios, Brannon C Springer, Robert A Hazlitt, David A Colby
Disubstituted hydroxylamines were synthesized and used to form aluminum-amide complexes. These reagents masked carbonyl groups in situ from nucleophilic addition. The stability and utility of the aluminum-aminals are presented in the context of selectively controlling nucleophilic addition on substrates with multiple carbonyl groups.
January 2015: Synthesis
https://www.readbyqxmd.com/read/25598556/-3-2-cycloaddition-reactions-of-oxyallyl-cations
#20
Hui Li, Jimmy Wu
The (3+2)-cycloaddition reaction involving oxyallyl cations has proven to be a versatile and efficient approach for the construction of five-membered carbo- and heterocycles, which are prevalent frameworks in natural products and pharmaceuticals. The following article will provide a brief summary of recent disclosures on this process featuring chemo-, regio- and diastereoselective oxyallyl cycloadditions with both electron-rich and electron-deficient 2π partners.
January 2015: Synthesis
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