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Organic Letters

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https://www.readbyqxmd.com/read/27808520/organocatalytic-synthesis-of-methylene-bridged-n-heterobiaryls
#1
David E Stephens, Vu T Nguyen, Bhuwan Chhetri, Emily R Clark, Hadi D Arman, Oleg V Larionov
A one-step synthesis of 1,1'- and 2,2'-methylene-bridged N-heterobiaryls directly from the corresponding N-heterocycles in a reaction with methylmagnesium chloride in the presence of catalytic amounts of N,N,N',N'-tetramethylethylenediamine under thermal and microwave conditions is reported. The split-and-merge methylenation of 2,2'-N-heterobiaryls and the direct ortho-alkylation of quinoline and isoquinoline with Grignard reagents have also been developed. Mechanistic studies identified several intermediates and provided insight into the formation and roles of magnesium hydride species in the process...
November 3, 2016: Organic Letters
https://www.readbyqxmd.com/read/27808517/pd-catalyzed-suzuki-miyaura-and-hiyama-denmark-couplings-of-aryl-sulfamates
#2
Patrick R Melvin, Nilay Hazari, Megan Mohadjer Beromi, Hemali P Shah, Michael J Williams
Using a recently discovered precatalyst, the first Pd-catalyzed Suzuki-Miyaura reactions using aryl sulfamates that occur at room temperature are reported. In complementary work, it is demonstrated that a related precatalyst can facilitate the coupling of aryl silanolates, which are less toxic and reactive nucleophiles than boronic acids with aryl chlorides. By combining our results using modern electrophiles and nucleophiles, the first Hiyama-Denmark reactions using aryl sulfamates are reported.
November 3, 2016: Organic Letters
https://www.readbyqxmd.com/read/27808516/dioxygen-promoted-pd-catalyzed-aminocarbonylation-of-organoboronic-acids-with-amines-and-co-a-direct-approach-to-tertiary-amides
#3
Long Ren, Xinwei Li, Ning Jiao
A direct approach from organoboronic acids and amines to tertiary amides via Pd-catalyzed aerobic aminocarbonylation has been developed. The presence of O2 significantly promotes the efficiency of this transformation. This method uses commercially available organoboronic acids and cheap CO and O2 (1 atm), which renders amides an easy synthesis with broad substrate scope and high functional group tolerance.
November 3, 2016: Organic Letters
https://www.readbyqxmd.com/read/27805818/pybidine-ni-oac-2-catalyzed-michael-aldol-reaction-of-methyleneindolinones-and-thiosalicylaldehydes-for-stereochemically-divergent-thiochromanyl-spirooxindoles
#4
Takayoshi Arai, Tomoya Miyazaki, Hiroki Ogawa, Hyuma Masu
(S,S)-Diphenylethylenediamine-derived bis(imidazolidine)pyridine (PyBidine)-Ni(OAc)2 complex catalyzed the asymmetric Michael/aldol reaction of methyleneindolinone and thiosalicylaldehyde to produce (2'R,3S,4'R)-thiochromanyl-spirooxindole having three contiguous stereogenic centers.
November 2, 2016: Organic Letters
https://www.readbyqxmd.com/read/27805816/synthesis-of-difluoroalkylated-arenes-by-hydroaryldifluoromethylation-of-alkenes-with-%C3%AE-%C3%AE-difluoroarylacetic-acids-under-photoredox-catalysis
#5
Bin Yang, Xiu-Hua Xu, Feng-Ling Qing
A visble-light-induced hydroaryldifluoromethylation of alkenes with α,α-difluoroarylacetic acids for preparation of difluoroalkylated arenes has been developed. This reaction proceeds through the hypervalent iodine reagent promoted decarboxylation and subsequent radical hydroaryldifluoromethylation.
November 2, 2016: Organic Letters
https://www.readbyqxmd.com/read/27805814/selective-%C3%AE-deuteration-of-amines-and-amino-acids-using-d2o
#6
Basujit Chatterjee, Varadhan Krishnakumar, Chidambaram Gunanathan
Monohydrido-bridged ruthenium complex [{(η(6)-p-cymene)RuCl}2(μ-H-μ-Cl)] catalyzes (catalyst load: 0.5-1 mol %) α-selective deuteration of primary and secondary amines, amino acids, and drug molecules using deuterium oxide (D2O) as a deuterium source. Mechanistic investigations revealed N-H activation of amines, which was also established by single-crystal X-ray analysis of an intermediate. β-Hydride elimination on amide ligand results in formation of imine-ligated ruthenium intermediate and subsequent 1,3-deuteride migrations to imine ligand leading to the selective deuteration at the α-CH2 protons of amine functionality is proposed...
November 2, 2016: Organic Letters
https://www.readbyqxmd.com/read/27805411/n-sulfanylethylaminooxybutyramide-seaoxy-a-crypto-thioester-compatible-with-fmoc-solid-phase-peptide-synthesis
#7
Shugo Tsuda, Masayoshi Mochizuki, Ken Sakamoto, Masaya Denda, Hideki Nishio, Akira Otaka, Taku Yoshiya
An N-sulfanylethylaminooxybutyramide (SEAoxy) has been developed as a novel thioester equivalent for native chemical ligation. SEAoxy peptide was straightforwardly synthesized by conventional Fmoc solid-phase peptide synthesis without a problem. Moreover, SEAoxy peptide could be directly applied to native chemical ligation owing to the intramolecular N-to-S acyl shift that releases the peptide-thioester in situ. This methodology was successfully applied to the synthesis of two bioactive peptides.
November 2, 2016: Organic Letters
https://www.readbyqxmd.com/read/27802059/agno2-as-the-no-source-for-the-synthesis-of-substituted-pyrazole-n-oxides-from-n-propargylamines
#8
Bingxiang Yuan, Fuming Zhang, Zhuomei Li, Shenghua Yang, Rulong Yan
A straightforward method for synthesizing the pyrazole N-oxides from N-propargylamines and AgNO2 through oxidation/cyclization reaction had been developed. AgNO2 was used as the NO source for the first time to synthesize pyrazole N-oxides. Various substituted groups on N-propargylamines proceeded smoothly, and the desired products were obtained in good yields.
November 1, 2016: Organic Letters
https://www.readbyqxmd.com/read/27802052/lanesoic-acid-a-cytotoxic-zwitterion-from-theonella-sp
#9
Jaime Rodríguez, Carlos Jiménez, María Blanco, Guillermo Tarazona, Rogelio Fernández, Carmen Cuevas
Lanesoic acid (1) was isolated and characterized from Theonella sp. during PharmaMar's ongoing program to study cytotoxic substances from marine sources. Its planar structure, elucidated by spectral analysis (NMR, IR, UV, and MS), possesses an unusual skeleton containing a tetrahydropyrimidine cation that is stabilized as a zwitterion by an internal carboxylate counterion. The stereostructure of 1 was deduced from ROESY-NOESY, J-based configurational analysis (JBCA), and density functional theory (DFT) computational calculations fitted using the recently published DP4+ parameter...
November 1, 2016: Organic Letters
https://www.readbyqxmd.com/read/27802047/dichotomy-of-reductive-addition-of-amines-to-cyclopropyl-ketones-vs-pyrrolidine-synthesis
#10
Oleg I Afanasyev, Alexey A Tsygankov, Dmitry L Usanov, Denis Chusov
An interesting catalytic dichotomy was discovered: switching between simple ligand-free catalysts leads to fundamentally different outcomes of reductive reaction between amines and α-carbonylcyclopropanes. Whereas a rhodium catalyst leads to the traditional reductive amination product, ruthenium catalysis enables a novel reaction of pyrrolidine synthesis via ring expansion. The protocols do not require an external hydrogen source and employ carbon monoxide as a deoxygenative agent. The developed methodologies are perfectly compatible with a number of synthetically important functionalities such as ester, carboxyl, bromo, and Cbz moieties...
November 1, 2016: Organic Letters
https://www.readbyqxmd.com/read/27802043/synthesis-of-the-gpr40-partial-agonist-mk-8666-through-a-kinetically-controlled-dynamic-enzymatic-ketone-reduction
#11
Alan M Hyde, Zhijian Liu, Birgit Kosjek, Lushi Tan, Artis Klapars, Eric R Ashley, Yong-Li Zhong, Oscar Alvizo, Nicholas J Agard, Guiquan Liu, Xiuyan Gu, Nobuyoshi Yasuda, John Limanto, Mark A Huffman, David M Tschaen
A scalable and efficient synthesis of the GPR40 agonist MK-8666 was developed from a simple pyridine building block. The key step to set the stereochemistry at two centers relied on an enzymatic dynamic kinetic reduction of an unactivated ketone. Directed evolution was leveraged to generate an optimized ketoreductase that provided the desired trans alcohol in >30:1 dr and >99% ee. Further, it was demonstrated that all four diastereomers of this hydroxy-ester could be prepared in high yield and selectivity...
November 1, 2016: Organic Letters
https://www.readbyqxmd.com/read/27797535/stereocontrolled-access-to-enantiopure-7-substituted-cis-and-trans-octahydroindoles
#12
Elena Ghirardi, Rosa Griera, Miriam Piccichè, Elies Molins, Israel Fernández, Joan Bosch, Mercedes Amat
Cyclocondensation of (R)-phenylglycinol with stereoisomeric mixtures (racemates, cis/trans) of 3-substituted 2-oxocyclohexaneacetates stereoselectively afforded tricyclic oxazoloindolone lactams, from which straightforward procedures for the stereocontrolled formation of enantiopure 7-substituted octahydroindoles with a variety of stereochemical patterns have been developed. The methodology has been successfully applied to the synthesis of (+)-α-lycorane.
October 31, 2016: Organic Letters
https://www.readbyqxmd.com/read/27797526/nucleophilic-tetrafluoroethylation-employing-in-situ-formed-organomagnesium-reagents
#13
Alena Budinská, Jiří Václavík, Václav Matoušek, Petr Beier
Tetrafluoroalkyl bromides are metalated with equimolar iPrMgCl·LiCl (Turbo Grignard) to form organomagnesium compounds which are stable at low temperatures and react with various electrophiles (aldehydes, ketones, CO2, cyclic sulfate and sulfamidate, N-sulfonylimines, nitrone, chlorophosphate, nonaflyl azide) to afford novel functionalized tetrafluoroethylene-containing products. Ease of operation, excellent selectivity, high nucleophilicity, and enhanced stability of the reactive species together with a broad substrate scope comprise a highly attractive nucleophilic tetrafluoroethylation protocol affording unique synthetic building blocks...
October 31, 2016: Organic Letters
https://www.readbyqxmd.com/read/27797211/electrostatically-enhanced-phosphoric-acids-a-tool-in-br%C3%A3-nsted-acid-catalysis
#14
Jie Ma, Steven R Kass
A novel type of phosphoric acid catalyst with enhanced reactivity is reported. These compounds possess one or two positively charged centers which electrostatically activate them. This is illustrated in several bond-forming transformations including Friedel-Crafts and Diels-Alder reactions as well as a ring-opening polymerization. Rate accelerations corresponding to orders of magnitude are observed.
October 31, 2016: Organic Letters
https://www.readbyqxmd.com/read/27797210/a-short-diastereoselective-total-synthesis-of-%C3%A2-vibralactone
#15
Alexander J Leeder, Robert J Heap, Lynda J Brown, Xavier Franck, Richard C D Brown
A total synthesis of the (±)-vibralactone has been achieved in 11 steps and 16% overall yield from malonic acid. Key steps include a highly diastereoselective allylation of an α-formyl ester containing an all carbon α-quaternary center, a Pd-catalyzed deallylative β-lactonization, and an aldehyde-selective Wacker oxidation of a terminal alkene.
October 31, 2016: Organic Letters
https://www.readbyqxmd.com/read/27797208/p-chlorobenzyl-ether-a-p-methoxybenzyl-ether-in-disguise
#16
Agnete H Viuff, Mads Heuckendorff, Henrik H Jensen
In the chemistry of polyfunctionalized organic compounds, protecting groups that can undergo mild and selective cleavage while still being stable during the entire synthetic sequence are often required. In this work, we present a straightforward conversion of the robust p-chlorobenzyl ether into the more labile and well-described p-methoxybenzyl ether using palladium catalysis. This reaction was demonstrated to be high yielding and compatible with a wide range of functionalities, thereby providing a useful supplement to the conventional ether protecting groups...
October 31, 2016: Organic Letters
https://www.readbyqxmd.com/read/27796096/high-valent-palladium-promoted-formal-wagner-meerwein-rearrangement
#17
Hongmiao Wu, Bin Yang, Lin Zhu, Ronghua Lu, Guigen Li, Hongjian Lu
An oxy-palladation, formal Wagner-Meerwein rearrangement and fluorination cascade has been established for generating fluorinated oxazolidine-2,4-diones and oxazolidin-2-ones. The reaction has a broad substrate scope in which both aryl and alkyl groups can be utilized as efficient migrating groups. Experimental evidence suggests that the reaction is initiated by anti-oxy-palladation of the olefin, followed by oxidative generation of an alkyl Pd(IV) intermediate and a concerted migration-fluorination.
October 31, 2016: Organic Letters
https://www.readbyqxmd.com/read/27792349/relay-rh-ii-pd-0-dual-catalysis-selective-construction-of-cyclic-all-quaternary-carbon-centers
#18
Zi-Sheng Chen, Xiao-Yan Huang, Jin-Ming Gao, Kegong Ji
A novel relay Rh(II)/Pd(0) dual catalysis strategy that promotes the divergent reaction of α-diazo-carbonyl compounds with allylic carboxylates for the selective construction of cyclic all-quaternary carbon centers has been developed. This binary catalyst system rendered domino C-H insertion/allylic alkylation process under mild conditions. Remarkably, the domino catalytic reaction shows good selectivity and excellent tolerance to various functionalities and is operationally simple.
October 28, 2016: Organic Letters
https://www.readbyqxmd.com/read/27792345/enantioselective-organocatalytic-synthesis-of-2-oxopiperazines-from-aldehydes-identification-of-the-elusive-epoxy-lactone-intermediate
#19
Nikolaos Kaplaneris, Constantinos Spyropoulos, Maroula G Kokotou, Christoforos G Kokotos
An organocatalytic linchpin catalysis approach was envisaged to convert simple aldehydes into enantioenriched 2-oxopiperazines. A four-step reaction sequence (chlorination, oxidation, substitution, and cyclization) was developed and led to different substitution patterns in high yields and selectivities. The reaction mechanism was studied, and the previously elusive epoxy lactone intermediate was identified by HRMS.
October 28, 2016: Organic Letters
https://www.readbyqxmd.com/read/27791384/synthesis-of-a-nucleobase-modified-protide-library
#20
Ling-Jie Gao, Steven De Jonghe, Piet Herdewijn
A new method for the construction of (aryloxy)phosphoramidate nucleoside prodrugs is presented. An (aryloxy)phosphoramidate ribose derivative as key building block was used for coupling with a number of nucleobases under Vorbrüggen reaction conditions yielding the protected ProTides in excellent yields. Selective hydrolysis of the acetoxy groups on the sugar moiety afforded a series of the desired ProTides. The advantage of this approach, when compared to classical procedures, is the greater flexibility for achieving structural variety of the nucleobase moiety...
October 28, 2016: Organic Letters
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