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Organic Letters

Pravin Patil, Rudrakshula Madhavachary, Katarzyna Kurpiewska, Justyna Kalinowska-Tłuścik, Alexander Dömling
The morpholine and piperazine with their remarkable physical and biochemical properties are popular heterocycles in organic and medicinal chemistry used in rational property design. However, in the majority of cases these rings are added to an existing molecule in a building block approach thus limiting their substitution pattern and diversity. Here we introduce a versatile de novo synthesis of the morpholine and piperazine rings using multicomponent reaction chemistry. The large scale amenable building blocks can be further substituted at up to four positions, making this a very versatile scaffold synthesis strategy...
January 19, 2017: Organic Letters
Elham Fadaei, Miguel Martín-Arroyo, Mohsen Tafazzoli, David González-Rodríguez
In contrast to more polar media, G-quadruplex assembly reveals remarkably high thermodynamic and kinetic stability in toluene solutions. Depending on the substituents installed at the lipophilic guanosine, either a dodecamer or an octamer complex is formed in the presence of K(+) or Na(+) salts that resist conditions of high dilution and elevated temperatures without exhibiting significant dissociation. Moreover, kinetic exchange between complexed and uncomplexed G is slow enough in NMR to monitor G-quadruplex formation along a day time scale...
January 19, 2017: Organic Letters
Yuanming Li, Armido Studer
The reaction of in situ generated arynes with aryl vinyl sulfoxides provides ortho-arylsulfinylaryl vinyl ethers via aryne σ-bond insertion into the S-O-bond and concomitant stereospecific S-O-vinyl migration. The cascade allows preparing di- or trisubstituted vinyl ethers with excellent stereospecificity. The reactions proceed under mild conditions, the substrate scope is broad, and the products obtained are valuable.
January 19, 2017: Organic Letters
Wei Yang, Jinhuan Dong, Jingyi Wang, Xianxiu Xu
An unprecedented Rh(III)-catalyzed annulation of various benzamides and acrylamides with quinone monoacetals was developed for the facile and efficient one-pot synthesis of bridged nine-membered benzo[c]azonine-1,5(2H)-diones and 2-azabicyclo[4.3.1]dec-4-ene-3,8-diones. It is the first example of synthesis of nine-membered heterocycles through Rh(III)-catalyzed C-H bond functionalization, and both aryl and vinyl C-H bonds are tolerant in this reaction. A plausible mechanism is proposed on the basis of control experiments...
January 19, 2017: Organic Letters
Guojun Wang, Jing Chen, Haining Zhu, Jürgen Rohr
Early acting cyclases play critical roles in programming the polyketide biosynthesis toward certain, distinguished scaffolds. Starting from acetyl-CoA and malonyl-CoA, a one-pot enzymatic total synthesis of an anthracyclinone scaffold, presteffimycinone, was achieved by mixing polyketide synthase (PKS) and early post-PKS enzymes from the biosynthetic pathways of three different types of type II-PKS driven anticancer antibiotics, namely, the mithramycin (aureolic acid-type), gilvocarcin (rearranged angucycline-type), and steffimycin (anthracycline) pathways...
January 19, 2017: Organic Letters
Kuo Xu, Peng-Fei Yang, Ya-Nan Yang, Zi-Ming Feng, Jian-Shuang Jiang, Pei-Cheng Zhang
An approach for discriminating the threo and erythro configurations of polyacetylene glycosides by (1)H NMR spectroscopy was developed. Using acetic acid-d4/D2O as the solvent, a relatively larger (3)JHH value (7.0 Hz) for the acyclic vicinal diol group was unambiguously assigned to the threo configuration, whereas the smaller value (3.5 Hz) was assigned to the erythro configuration. This convenient method requires no hydrolysis or derivatization and is suitable for micromolar concentrations of polyacetylene glycosides...
January 19, 2017: Organic Letters
Shaofang Zhou, Tao Song, He Chen, Zhonglin Liu, Haigen Shen, Chaozhong Li
The trifluoromethylalkynylation of unactivated alkenes with alkynyl sulfones and Togni's reagent was developed. The reaction was catalyzed by 2,4,6-trimethylpyridine, leading to various β-trifluoromethylated alkynes under metal-free conditions with a broad substrate scope and wide functional group compatibility. A mechanism involving catalytic nonchain radical processes is proposed.
January 19, 2017: Organic Letters
Woon Young Song, Dawa Jeong, Jimin Kim, Min Wook Lee, Man Hwan Oh, Hak Joong Kim
Acinetobactin is a major siderophore utilized by the human pathogen Acinetobacter baumannii. The rapid acquisition of drug resistance by A. baumannii has garnered concern globally. Herein, acinetobactin and systematically generated analogues were prepared and characterized; the binding and cellular delivery of Fe(III) by the analogues were evaluated. This investigation not only led to the clarification of the physiologically relevant acinetobactin structure but also revealed several key structural elements for its functionality as a siderophore...
January 19, 2017: Organic Letters
Yusuke Saga, Takeshi Araki, Hiroshi Araya, Kazuki Saito, Mami Yamazaki, Hideyuki Suzuki, Tetsuo Kushiro
Ferns are known to produce onoceroids including onoceranes and serratanes having unusual structures among triterpenes. From the fern Lycopodium clavatum, a novel onoceroid synthase gene was cloned that showed high sequence identity with a previously identified α-onocerin synthase. Functional analysis by coexpression with pre-α-onocerin synthase in yeast led to the production of tohogenol and serratenediol. The result suggested that serratanes are directly biosynthesized from pre-α-onocerin and not from α-onocerin as previously assumed...
January 19, 2017: Organic Letters
Junbin Tang, Shiqing Li, Zheng Liu, Yinsong Zhao, Zhijie She, Vilas D Kadam, Ge Gao, Jingbo Lan, Jingsong You
A cascade double C-H annulation of aldoximes with alkynes to produce benz[a]acridizinium salts is developed by using a simple catalytic system of [Cp*Rh(OAc)2]2 in the presence of Zn(OTf)2 with oxygen as the sole oxidant. In addition, the challenging C-H annulation of aldoximes with alkynes, especially arylalkynes, to synthesize 1H-isoquinolines is also achieved under slightly modified conditions. This protocol provides an efficient one-pot access to multisubstituted dehydroberberinium skeletons from simple starting materials, which can be easily transformed into berberinium and tetrahydroberberine skeletons by controlled hydrogenation...
January 19, 2017: Organic Letters
Rongrong Lin, Liya Cao, F G West
A novel approach to medium-sized cyclic ethers was devised using a Stevens [1,2]-shift of a sulfonium ylide derived from a readily accessible six-membered mixed-monothioacetal precursor. The concise and efficient transformation offers a surprising degree of chirality transfer with observed retention of stereochemical configuration on the anomeric migrating carbon and has been applied as the key step in an enantioselective formal synthesis of (+)-laurencin.
January 19, 2017: Organic Letters
Julien Maury, Wojciech Zawodny, Jonathan Clayden
Treatment of N'-aryl urea derivatives of enantiomerically enriched α-(2-pyridyl) and α-(3-pyridyl)alkylamines with a base leads to the migration of the N'-aryl substituent from N to C in a 'nonclassical' intramolecular nucleophilic aromatic substitution reaction. Both electron-rich and -poor rings migrate successfully. A new quaternary stereogenic center is formed adjacent to the pyridine ring with high stereospecificity, even when the intermediate anion is a presumably planar 2-picolyllithium. Base hydrolysis of the urea gives enantiomerically enriched α-pyridylalkylamines...
January 18, 2017: Organic Letters
Juliette Halli, Michael Bolte, Jan Bats, Georg Manolikakes
A two-step reaction sequence for the highly stereodivergent construction of 1,3-diamines with three continuous stereocenters is reported. This novel method enables the controlled synthesis of any given diastereomer of the 1,3-diamine scaffold from a simple set of starting materials in a highly modular manner. The disclosed approach is based on the reaction of an enamide with an in situ generated N-acylimine followed by a subsequent trapping of the generated intermediate with a suitable nucleophile. By careful choice of starting materials, reagents, and reaction conditions, each stereocenter can be constructed in a highly selective fashion...
January 18, 2017: Organic Letters
Anupam Jana, Karol Grela
An easy and mild functionalization method of tetraoxane derivatives via olefin metathesis is reported. This reaction offers a new method to afford fully functionalized tetraoxanes in high yields. This method is also utilized in the functionalization of bioactive compounds.
January 17, 2017: Organic Letters
Shota Mizuno, Shou Terasaki, Toru Shinozawa, Motoi Kawatsura
The ruthenium-catalyzed regioselective allylic amination of tertiary allylic acetates with several types of amines has been accomplished. The reaction was effectively catalyzed by Cp*RuCl2/5,5'-dimethyl-2,2'-bipyridine or its related ruthenium catalyst systems, and α,α-disubstituted allylic amines were formed as a single regioisomer in moderate to high yields.
January 17, 2017: Organic Letters
Robin Wehlauch, Simone M Grendelmeier, Hideki Miyatake-Ondozabal, Alexander H Sandtorv, Manuel Scherer, Karl Gademann
The synthesis of the Securinega alkaloid secu'amamine E (ent-virosine A) has been accomplished for the first time in 12 steps and 8.5% overall yield. In addition, bubbialine has been prepared and characterized. These two alkaloids and bubbialidine, all featuring an azabicyclo[2.2.2]octane core, were rearranged to their azabicyclo[3.2.1]octane congeners, a framework found in many Securinega alkaloids. These experiments suggest that azabicyclo[2.2.2]octane derivatives could serve as intermediates in the biosynthesis of the rearranged azabicyclo[3...
January 17, 2017: Organic Letters
Melissa Lee, Melanie S Sanford
This letter describes the development of a method for selective remote C(sp(3))-H oxygenation of protonated aliphatic amines using aqueous potassium persulfate. Protonation serves to deactivate the proximal C(sp(3))-H bonds of the amine substrates and also renders the amines soluble in the aqueous medium. These reactions proceed under relatively mild conditions (within 2 h at 80 °C with amine as limiting reagent) and do not require a transition metal catalyst. This method is applicable to a variety of types of C(sp(3))-H bonds, including 3°, 2°, and benzylic C-H sites in primary, secondary, and tertiary amine substrates...
January 17, 2017: Organic Letters
Isai Ramakrishna, Vinod Bhajammanavar, Sumitava Mallik, Mahiuddin Baidya
A practical and step-economical nitroso aldol reaction has been developed based on metal-free direct cross-coupling of ready-stock anilines with silyl enol ethers at room temperature affording α-amino ketones in high yields (up to 82%). The protocol features a one-pot cascade of nitroso compound generation, selective C-N bond formation, and N-O bond cleavage using solely inexpensive and user-friendly Oxone and displays remarkable functional group tolerance. The method was further extended to prepare densely functionalized indoles that are otherwise difficult to synthesize...
January 17, 2017: Organic Letters
Xing-Hao Huang, Ling-Xue Tao, Chang-Qiang Ke, Chunping Tang, Hai-Yan Zhang, Yang Ye, Li-Gen Lin, Sheng Yao
Two dimeric diterpenoids, taxodikaloids A (1) and B (2), have been identified from the seeds of Taxodium ascendens. The diterpenoid structures were established on the basis of comprehensive spectroscopic analysis, and the absolute configuration of taxodikaloid A (1) was further confirmed by single-crystal X-ray diffraction. Both structures feature an unprecedented oxazoline ring linkage connecting two abietane diterpenoid monomers. A plausible biosynthetic pathway for compounds 1 and 2 is proposed. Both compounds show potential neuroprotective activity against Aβ25-35-induced damage in SH-SY5Y cells...
January 17, 2017: Organic Letters
Serena Mantenuto, Cecilia Ciccolini, Simone Lucarini, Giovanni Piersanti, Gianfranco Favi, Fabio Mantellini
A Pd(II)-catalyzed intramolecular oxidative C-H/C-H cross-coupling has been developed for the direct construction of valuable polycyclic heteroarene scaffolds. From a retrosynthetic point of view, the strategic formation of a C-C bond via C(sp(2))-H/C(sp(2))-H dehydrogenative coupling across C3,N-linked biheterocyclic precursors may be useful in de novo syntheses of indole-derived natural products and pharmaceuticals. The reaction exhibited good functional group/heterocycle tolerance, and a proposed mechanism involving an azoylpalladium complex is also supported...
January 17, 2017: Organic Letters
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