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Organic Letters

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https://www.readbyqxmd.com/read/30240223/iridium-catalyzed-enantioselective-and-diastereoselective-allylation-of-dioxindoles-a-one-step-synthesis-of-3-allyl-3-hydroxyoxindoles
#1
Rui He, Shanchao Wu, Haoming Tang, Xiaohong Huo, Zhenliang Sun, Wanbin Zhang
An iridium-catalyzed asymmetric allylation of dioxindoles, 3-hydroxyoxindoles, regulated by prosthetic groups has been accomplished under mild conditions. The methodology is applicable to a diverse array of 3-hydroxyoxindole and cinnamyl acetate substrates. A range of 3-allyl-3-hydroxyoxindoles containing vicinal tetrasubstituted and trisubstituted stereocenters can be efficiently synthesized in one-step with excellent enantioselectivity (up to >99% enaniomeric excess (ee)) and good diastereoselectivity (up to 11:1 diastereomeric ratio (dr))...
September 21, 2018: Organic Letters
https://www.readbyqxmd.com/read/30239209/palladium-catalyzed-2-2-2-annulation-via-transformations-of-multiple-c-h-bonds-one-pot-synthesis-of-diverse-indolo-3-2-a-carbazoles
#2
K Shiva Kumar, Siddi Ramulu Meesa, Praveen Kumar Naikawadi
A Pd-catalyzed novel cascade reaction has been developed for the synthesis of indolo[3,2 a]carbazoles involving multiple C-H transformation-annulations between the indoles and alkynes. The method involves molecular oxygen as the sole oxidant and is an effective and step-economic process.
September 21, 2018: Organic Letters
https://www.readbyqxmd.com/read/30234993/well-defined-phosphine-free-iron-catalyzed-n-ethylation-and-n-methylation-of-amines-with-ethanol-and-methanol
#3
Alexis Lator, Sylvain Gaillard, Albert Poater, Jean-Luc Renaud
An iron(0) complex bearing a cyclopentadienone ligand catalyzed N-methylation and N-ethylation of aryl and aliphatic amines with methanol or ethanol in mild and basic conditions through a hydrogen autotransfer borrowing process is reported. A broad range of aromatic and aliphatic amines underwent mono- or dimethylation in high yields. DFT calculations suggest molecular hydrogen acts not only as a reducing agent but also as an additive to displace thermodynamic equilibria.
September 20, 2018: Organic Letters
https://www.readbyqxmd.com/read/30234990/diastereoselective-synthesis-of-tetrahydroquinolines-via-4-2-annulation-between-in-situ-generated-p-quinone-methides-and-nitroalkenes
#4
Junwei Wang, Xiang Pan, Jian Liu, Lin Zhao, Ying Zhi, Kun Zhao, Lihong Hu
A formal [4 + 2] annulation reaction between in situ generated p-quinone methides and nitroalkenes via an aza-Michael/1,6-conjugate addition reaction sequence has been developed in which manganese dioxide is used as the oxidant to promote in situ formation of o-tosylaminophenyl-substituted p-QMs. Under mild conditions, this unprecedented cascade reaction readily occurs in good yield, providing straightforward access to a series of 4-aryl-substituted tetrahydroquinolines.
September 20, 2018: Organic Letters
https://www.readbyqxmd.com/read/30234313/structures-and-synthesis-of-hitoyopodins-bioactive-aromatic-sesquiterpenoids-produced-by-the-mushroom-coprinopsis-cinerea
#5
Junnosuke Otaka, Takeshi Shimizu, Yushi Futamura, Daisuke Hashizume, Hiroyuki Osada
The structures of sesquiterpenoids hitoyopodin A (1) and its hydroxy derivatives 2 and 3 from the mushroom Coprinopsis cinerea are reported. Their absolute structures (1-3) with a benzoxabicyclo[3.2.1]octane core were determined by spectroscopy, X-ray crystallography, and total synthesis of 1. Compound 1 displays antiproliferative activity against HL-60 cancer cells and the malarial parasite Plasmodium falciparum. It is proposed that 1 acts as a crucial precursor in the biosynthesis of 2, 3, and lagopodins.
September 20, 2018: Organic Letters
https://www.readbyqxmd.com/read/30234312/asymmetric-c%C3%AE-alkylation-of-proline-via-chirality-transfers-of-conformationally-restricted-proline-derivative-application-to-the-total-synthesis-of-amathaspiramide-f
#6
Hyunkyung Cho, Jae Eui Shin, Seokwoo Lee, Hongjun Jeon, Soojun Park, Sanghee Kim
An efficient strategy for the asymmetric synthesis of Cα-tetrasubstituted proline derivatives from proline has been established. A nitrogen-fused bicyclic system was devised to control the stereodynamics of proline. Through N-quaternizations with allylic electrophiles followed by [2,3]-rearrangements, the bicyclic proline system delivered enantioenriched Cα-tetrasubstituted prolines. This strategy was applied to the concise total synthesis of (-)-amathaspiramide F.
September 20, 2018: Organic Letters
https://www.readbyqxmd.com/read/30234310/metal-free-formal-inverse-electron-demand-diels-alder-reaction-of-1-2-diazines-with-ynamides
#7
Jian Xue, Erhui Gao, Xiao-Na Wang, Junbiao Chang
A highly effective metal-free formal inverse-electron-demand Diels-Alder reaction of 1,2-diazines with ynamides has been developed. This catalytic protocol is more environmentally friendly and allows for the construction of 2-aminonaphthalenes and 2-aminoanthracenes from 1,2-diazines and ynamides in good to high yields with wide diversity and functional group tolerance.
September 20, 2018: Organic Letters
https://www.readbyqxmd.com/read/30234309/glucosyltransferase-capable-of-catalyzing-the-last-step-in-neoandrographolide-biosynthesis
#8
Yuan Li, Hui-Xin Lin, Jian Wang, Jian Yang, Chang-Jiang-Sheng Lai, Xing Wang, Bao-Wei Ma, Jin-Fu Tang, Yong Li, Xin-Lin Li, Juan Guo, Wei Gao, Lu-Qi Huang
ApUGT, a diterpene glycosyltransferase from Andrographis paniculata, could transfer a glucose to the C-19 hydroxyl moiety of andrograpanin to form neoandrographolide. This glycosyltransferase has a broad substrate scope, and it can glycosylate 26 natural and unnatural compounds of different structural types. This study provides a basis for exploring the glycosylation mechanism of ent-labdane-type diterpenes and plays an important role in diversifying the structures used in drug discovery.
September 20, 2018: Organic Letters
https://www.readbyqxmd.com/read/30234306/palladium-0-catalyzed-intermolecular-cascade-dearomatization-reaction-of-%C3%AE-naphthol-derivatives-with-propargyl-carbonates
#9
Lu Ding, Shu-Li You
A Pd(0)-catalyzed intermolecular cascade dearomatization reaction of β-naphthol derivatives with propargyl carbonates was described. In the presence of a Pd complex derived from Pd2 dba3 and rac-BINAP, various spironaphthalenones were obtained in excellent yields (up to 95%) and with high chemoselectivity (C/O > 20:1) in most cases.
September 20, 2018: Organic Letters
https://www.readbyqxmd.com/read/30232898/enantioselective-and-divergent-syntheses-of-alstoscholarisines-a-e-and-their-enantiomers
#10
Lu Hu, Qi Li, Licheng Yao, Bai Xu, Xia Wang, Xuebin Liao
Concise, enantioselective, and divergent syntheses of alstoscholarisines A and E are presented in 8 and 9 steps, respectively; alstoscholarisine E has never been accessed before. A boron-mediated aldol reaction and Rh-catalyzed cycloisomerization were exploited to access stereoisomers 8 and 9 as key intermediates. The challenging sterically congested alstoscholarisine core was furnished by a reductive transannular cyclization in the final steps. This strategy was also used for the syntheses of enantiomers of alstoscholarisines A and E...
September 20, 2018: Organic Letters
https://www.readbyqxmd.com/read/30232896/total-synthesis-of-asperphenins-a-and-b
#11
Jia-Lei Yan, Yingying Cheng, Jing Chen, Ranjala Ratnayake, Long H Dang, Hendrik Luesch, Yian Guo, Tao Ye
The first total synthesis of asperphenins A and B has been accomplished in a concise, highly stereoselective fashion from commercially available materials (15 steps, 9.7% and 14.2% overall yields, respectively). The convergent route featured the judicious choice of protecting groups, fragment assembly strategy and a late-stage iron-catalyzed Wacker-type selective oxidation of an internal alkene to the corresponding ketone.
September 20, 2018: Organic Letters
https://www.readbyqxmd.com/read/30232895/iridium-catalyzed-unreactive-c-sp-3-h-amination-with-2-2-2-trichloroethoxycarbonyl-azide
#12
Tao Zhang, Xuejiao Hu, Xunqing Dong, Guigen Li, Hongjian Lu
An additive-assisted iridium-catalyzed directed C(sp3 )-H amination with 2,2,2-trichloroethoxycarbonyl azide as an amino source is reported. Both carboxylate anions and the corresponding cations in the additives are crucial to achieve satisfactory efficiency. Sodium acetate or n-pentanoic acid can promote the amination of various primary C(sp3 )-H bonds adjacent to secondary, tertiary, and quaternary carbons in ketoximes or N-aromatic heterocycles, respectively, providing a practical route to versatile β-amino ketoxime and N-heteroaryl ethanamine derivatives...
September 20, 2018: Organic Letters
https://www.readbyqxmd.com/read/30232894/rhodium-catalyzed-arylzincation-of-alkynes-ligand-control-of-1-4-migration-selectivity
#13
Jialin Ming, Tamio Hayashi
The addition of arylzinc reagents ArZnCl 1 to alkynes 2 was found to be catalyzed by rhodium complexes in the presence of a catalytic amount of zinc chloride. The selectivity in giving 2-arylalkenylzinc species 3 or ortho-alkenylarylzinc species 4, the latter of which is generated through 1,4-Rh migration from alkenyl to aryl in the catalytic cycle, is controlled by the ligands on rhodium. Ligands cod and binap gave 3 and 4, respectively, with high selectivity.
September 20, 2018: Organic Letters
https://www.readbyqxmd.com/read/30232893/palladium-mediated-site-selective-c-h-radio-iodination
#14
Emmanuelle Dubost, Victor Babin, Florian Benoist, Alexandra Hébert, Pierre Barbey, Céline Chollet, Jean-Philippe Bouillon, Alain Manrique, Grégory Pieters, Frédéric Fabis, Thomas Cailly
The palladium-mediated C-H radio-iodination of arenes using sodium iodide as the primary isotopic source is reported and performed without chemical know-how in 30 min and applied to the synthesis of complex radio-iodinated compounds of biological interest.
September 20, 2018: Organic Letters
https://www.readbyqxmd.com/read/30232891/zn-oac-2-catalyzed-c3-carbonylacetylation-of-indoles-with-%C3%AE-diazoketones-involving-wolff-rearrangement
#15
Xinwei Hu, Fengjuan Chen, Yuanfu Deng, Huanfeng Jiang, Wei Zeng
Zn(OAc)2 -catalyzed highly regioselective carbonylacetylation of indoles and pyrroles with α-diazoketones has been developed. This transformation involves a combination of Wolff rearrangement/cross-coupling relay and provides an efficient approach to versatile 3-carbonylacetylindoles and 2-carbonylacetylpyrroles with a broad range of functional group tolerance.
September 20, 2018: Organic Letters
https://www.readbyqxmd.com/read/30230341/diversity-oriented-syntheses-of-%C3%AE-substituted-%C3%AE-amino-%C3%AE-lactam-peptide-mimics-with-constrained-backbone-and-side-chain-residues
#16
Azade Geranurimi, William D Lubell
α- N-(Fmoc)Amino-γ-lactam dipeptides with a variety of β-substituents were synthesized stereoselectively with minimal β-elimination by routes employing, respectively, Mitsunobu chemistry and cyclic sulfamidate nucleophilic ring opening from trans- and cis-β-hydroxy-α-amino-γ-lactam precursors. This diversity-oriented method provides stereochemically pure dipeptide mimics bearing Cys, Ser, Thr, Dap, Dab, His, and other amino acid residues with constrained backbone and side chain conformations.
September 19, 2018: Organic Letters
https://www.readbyqxmd.com/read/30230338/total-biosynthesis-of-brassicicenes-identification-of-a-key-enzyme-for-skeletal-diversification
#17
Akihiro Tazawa, Ying Ye, Taro Ozaki, Chengwei Liu, Yasushi Ogasawara, Tohru Dairi, Yusuke Higuchi, Nobuo Kato, Katsuya Gomi, Atsushi Minami, Hideaki Oikawa
The biosynthetic pathway of brassicicenes, derived from the phytopathogen Pseudocercospora fijiensis, was fully reconstituted. Heterologous expression of the eight genes highly expressed in infected leaf tissues generated a new brassicicene derivative as a final product. Together with the characterization of P450 from Alternaria brassicicola, a late stage of the biosynthetic pathway, which generates remarkable structural diversity, has been proposed. Notably, a unique P450 that converts 3 to the structurally distinct 4 and 6 was identified...
September 19, 2018: Organic Letters
https://www.readbyqxmd.com/read/30226789/selective-oxidative-dearomatization-of-angular-tetracyclic-phenols-by-controlled-irradiation-under-air-synthesis-of-an-angucyclinone-type-double-peroxide-with-anticancer-properties
#18
María J Cabrera-Afonso, Silvia R Lucena, Ángeles Juarranz, Antonio Urbano, M Carmen Carreño
Angular tetracyclic p-peroxyquinols, p-quinols, and a pentacyclic double peroxide, showing anticancer properties, were synthesized from the corresponding phenols by an environmentally friendly solvent- and wavelength-controlled irradiation under air in the absence of an external photosensitizer.
September 18, 2018: Organic Letters
https://www.readbyqxmd.com/read/30226784/chemical-ecogenomics-guided-discovery-of-phytotoxic-%C3%AE-pyrones-from-the-fungal-wheat-pathogen-parastagonospora-nodorum
#19
Hang Li, Jinyu Hu, Haochen Wei, Peter S Solomon, Daniel Vuong, Ernest Lacey, Keith A Stubbs, Andrew M Piggott, Yit-Heng Chooi
A biosynthetic gene cluster that is significantly upregulated in the fungal wheat pathogen Parastagonospora nodorum during plant infection was reconstructed heterologously in Aspergillus nidulans. This led to the discovery of five new α-pyrone polyketides, alternapyrones B-F (2-6). Compounds 5 and 6, which contain a highly substituted dihydrofuran, exhibited phytotoxicity on wheat seed germination. It is demonstrated that only three enzymes, one highly reducing polyketide synthase and two multifunctional P450 oxygenases, are needed to synthesize the structurally complex products...
September 18, 2018: Organic Letters
https://www.readbyqxmd.com/read/30226778/2-6-bis-trifluoromethyl-phenylboronic-esters-as-protective-groups-for-diols-a-protection-deprotection-protocol-for-use-under-mild-conditions
#20
Naoyuki Shimada, Sari Urata, Kenji Fukuhara, Takao Tsuneda, Kazuishi Makino
The application of 2,6-bis(trifluoromethyl)phenyl boronic acid ( o-FXylB(OH)2 ; o-FXyl = 2,6-(CF3 )2 C6 H3 ) as a recoverable and reusable protective agent for diols is described. The resulting cyclic boronic esters are water- and air-stable and tolerant to various organic transformations. Moreover, they can be deprotected under mild conditions. This methodology was applied to the synthesis of a highly conjugated enetriyne natural product with anti-angiogenic activities.
September 18, 2018: Organic Letters
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