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Organic Letters

Dong Wang, Kálmán J Szabó
In this study, we present the synthesis of new, stereodefined allylboronic acids employed to investigate the stereochemistry of the Cu-catalyzed cross-coupling of allylboronic acids with α-diazoketones. According to our results, this reaction proceeds with retention of the relative configuration of the allylboronic acid substrate. We suggest that the stereoinduction step involves a syn SE2'-type transmetalation of the allylboronic acid substrate with a Cu-carbene species.
March 23, 2017: Organic Letters
Chunxia Wang, Luoqiang Zhang, Jingsong You
Nickel-catalyzed aminoxylation of an unactivated C(sp(3))-H bond with a stable nitroxyl radical has been accomplished for the first time to offer various N-alkoxyamine derivatives, which further enables a one-pot approach to α-formyl acid derivatives. The aminoxylation process reported also provides direct evidence for the oxidative addition of a cyclometallic intermediate with a free radical, which is helpful for the reaction-mechanism study in transition-metal-catalyzed functionalization of inert C(sp(3))-H bonds...
March 23, 2017: Organic Letters
Hui Sun, Bin Cui, Lili Duan, Yue-Ming Li
The preparation of prolinol ether type compounds was realized via MnI2-catalyzed intramolecular iodoamination of unfunctionalized olefins and subsequent ring opening of an aziridinium ion intermediate with alcohols/phenols. In the presence of a catalytic amount of MnI2 and 2 equiv of NaI, intramolecular aminoalkoxylation of different N-benzyl-5-methylhex-4-en-1-amine substrates proceeded readily in alcoholic solvents, leading to 2-(alkoxyalkyl)pyrrolidine products in up to 90% isolated yields.
March 23, 2017: Organic Letters
Subramani Sangeetha, Govindasamy Sekar
An efficient protocol is described for the synthesis of 2-acylbenzo[b]thiophenes from easily accessible 2-iodochalcones through α-C-H functionalization using Cu(OAc)2 catalyst and xanthate as sulfur source. Less reactive 2-bromochalcones also yielded the corresponding 2-acylbenzothiophenes in good yield. The reaction proceeds via in situ incorporation of sulfur followed by copper-catalyzed cyclization to generate 2-acylbenzothiophenes without external acyl source. The synthetic importance is showcased by synthesis of 1-(5-hydroxybenzothiophene-2-yl)ethanone, which is a known pre-mRNA splicing modulator...
March 23, 2017: Organic Letters
Yang Gui, Shi-Kai Tian
A one-pot protocol has been developed for sequential benzyne activation and nucleophilic substitution of enantioenriched tertiary benzylic amines. In the presence of 2-(trimethylsilyl)phenyl triflate and CsF, a range of enantioenriched tertiary benzylic amines were substituted by various nucleophiles, delivering structurally diverse benzylic compounds in moderate to excellent yields with excellent retention of enantiopurity. Importantly, this operationally simple protocol permitted formation of various chiral C-S, C-Se, C-C, and C-N bonds with excellent enantiopurity under metal-free conditions...
March 23, 2017: Organic Letters
Ina Scheipers, Eva Koch, Armido Studer
Palladium-catalyzed γ-arylation of acyclic β,γ-unsaturated carboxylic acids with various aryl iodides is reported. The cascade comprises a decarboxylative γ-palladation of β,γ-unsaturated α,α'-disubstituted carboxylic acids and subsequent C(sp(2))-C(sp(3)) bond formation to provide diaryl vinyl methanes in moderate to good yields and high E/Z-selectivities. Reaction with an enantiomerically pure acid revealed that the process occurs with high stereospecificity.
March 23, 2017: Organic Letters
Jian Chang, Cong Xu, Jie Gao, Fengyun Gao, Dongsheng Zhu, Mang Wang
A complete self-assistance strategy based on Me3SiCF2Br was used in the domino conversion of methylvinylketones into α,α-difluorinated cyclopentanones. Initiated by 5 mol % of nBu4NBr, the multistep reaction occurred in one pot under mild conditions via the in situ formation of silyl dienol ethers, difluorocyclopropanation, thermal vinylcyclopropane-cyclopentene rearrangement, and desilylation. The process takes advantage of the multitasking capability of Me3SiCF2Br as the difluorocarbene source, a silicon-based transfer agent, and a bromine anion releaser...
March 23, 2017: Organic Letters
Paul O Guillen, Karla B Jaramillo, Gregory Genta-Jouve, Frederic Sinniger, Jenny Rodriguez, Olivier P Thomas
The first chemical study of the common species Terrazoanthus onoi, present off the coast of Ecuador, led to the identification of a new family of 2-aminoimidazole alkaloids named terrazoanthines A-C (1-3). Homologues 1 and 2 feature an unprecedented 6-(imidazol-5-yl)benzo[d]imidazole. Acyl substitution pattern and complete configurational assignments were deduced from comparison between experimental and theoretical (13)C NMR and ECD data, respectively. These compounds may represent key derivatives in the biosynthesis of zoanthoxanthins...
March 23, 2017: Organic Letters
Gerui Ren, Qinheng Zheng, Hua Wang
A chemoselective Staudinger reduction/sulfur(VI) fluoride exchange cascade has been developed to join two chemical segments through an aryl sulfamate ester (RNH-SO2-OAr) linkage. Aryl fluorosulfate is exploited in this work as the first tetrahedral electrophilic trap for the in situ generated iminophosphorane. Ten examples using azide-containing compounds are presented.
March 23, 2017: Organic Letters
Taimin Wang, Xiaoguang Duan, Hua Zhao, Shengxian Zhai, Cheng Tao, Huifei Wang, Yun Li, Bin Cheng, Hongbin Zhai
An asymmetric total synthesis of (-)-aspidophylline A has been accomplished. The key transformations include an asymmetric hydride transfer hydrogenation of an α,β-acetylenic ketone and a cationic gold(I)-catalyzed 6-exo-dig cyclization involving an alkynylindole/aminal formation cascade, which enables stereoselective establishment of the requisite quaternary carbon center.
March 23, 2017: Organic Letters
Giorgos S Koutoulogenis, Maroula G Kokotou, Errika Voutyritsa, Dimitris Limnios, Christoforos G Kokotos
A novel and efficient metal-free catalyzed hydroacylation of dialkyl azodicarboxylates is reported. Graphite flakes were found to be the most efficient catalyst among other carbon-based materials to promote this reaction. This unprecedented catalytic activity can be expanded into a wide substrate scope of aliphatic aldehydes bearing various functional groups, leading to the corresponding products in good to excellent yields.
March 23, 2017: Organic Letters
Chieh-Kai Chan, Yu-Lin Tsai, Meng-Yang Chang
CuI/DMSO-mediated intramolecular cycloacetalization/ketalization of o-carbonyl allylbenzenes has been achieved for constructing [6,6,5]-tricycles having a ketal motif in good yields. The expeditious one-step route provides a three C-O bond formation. The key products with the structural framework of a benzofused dioxabicyclo[3.2.1]octane core have been confirmed by X-ray crystallographic analysis. Synthesis of dihydroisocoumarin has been studied.
March 23, 2017: Organic Letters
Bin Zhang, Xiaofei Zhang, Jian Hao, Chunhao Yang
A mild and efficient synthesis of N-substituted-2-fluoroindole derivatives was achieved via Buchwald-Hartwig couplings and a sequential, base-promoted intramolecular nucleophilic reaction-β-fluorine elimination. By employing easily obtained gem-difluorostyrenes and primary arylamines, the scope, advantages, and limitations of this reaction were well investigated. Furthermore, this strategy distinguishes itself by high modularity, operational simplicity, and a wide substrate scope, giving rise to a broad array of 2-fluoroindole derivatives in moderate to excellent yields...
March 23, 2017: Organic Letters
Douglas L Orsi, Brandon J Easley, Ashley M Lick, Ryan A Altman
A nucleophilic addition reaction of aryl thiols to readily available β,β-difluorostyrenes provides α,α-difluoroalkylthioethers. The reaction proceeds through an unstable anionic intermediate, prone to eliminate fluoride and generate α-fluorovinylthioethers. However, the use of base catalysis overcomes the facile β-fluoride elimination, generating α,α-difluoroalkylthioethers in excellent yields and selectivities.
March 23, 2017: Organic Letters
Huamin Wang, Wei Zhou, Mengna Tao, Anjing Hu, Junliang Zhang
The development of electron-demand disfavored [4 + 2] cycloaddition of two electron-deficient reacting partners poses a considerable challenge. An enantioselective aza-[4 + 2] cycloaddition of electron-deficient N-sulfonyl-1-aza-1,3-dienes is possible with vinyl ketones via phosphine catalysis, which provides facile access to a wide range of enantioenriched trifluoromethylated tetrahydropyridines in up to 97% yield with 97% ee and >20:1 dr. The mechanistic study indicated that this cycloaddition proceeds via a tandem intermolecular aza-Rauhut-Currier/intramolecular aza-Michael addition reaction...
March 22, 2017: Organic Letters
Ren Zhao, Wenjun Lu
A β-mesylation of primary sp(3) C-H bonds from simple amides with methanesulfonic anhydride (Ms2O) has been established successfully at 80 °C in a Pd(OAc)2 (catalyst)/K2S2O8 (oxidant)/CF3CH2OH (solvent) system. These amide substrates involve N-monosubstituted linear, branch, or cyclic alkanes, and electron-deficient benzyl compounds. The β-mesylated amide products can be converted easily to β-fluoroamides or β-lactams through inter- or intramolecular SN2 processes.
March 22, 2017: Organic Letters
Santanu Jana, Sumana Mondal, Suvarn S Kulkarni
Herein, we report, for the first time, a strategy to differentiate O4/O4' positions of 1,1'-α,α-trehalose via regioselective protection or site-selective functionalization and its application in the first chemical synthesis of succinoyl trehalose lipids. The biosurfactant glycolipids were obtained in 11-12 steps starting from trehalose in time span of 8-10 days and 11-12% overall yields.
March 22, 2017: Organic Letters
Gaochao Huang, Ruben Shrestha, Kaimin Jia, Brian V Geisbrecht, Ping Li
A four-step enantioselective approach was developed to synthesize anti (1R,2S)-1a and (1S,2R)-1b containing a β-O-4 linkage in good yields. A significant difference was observed for the apparent binding affinities of four stereospecific lignin model compounds with TcDyP by surface plasmon resonance, which was not translated into a significant difference in enzyme activities. The discrepancy may be attributed to the conformational change involving a loop widely present in DyPs upon H2O2 binding.
March 22, 2017: Organic Letters
Thomas P Wyche, Antonio C Ruzzini, Christine Beemelmanns, Ki Hyun Kim, Jonathan L Klassen, Shugeng Cao, Michael Poulsen, Tim S Bugni, Cameron R Currie, Jon Clardy
Three new dentigerumycin analogues are produced by Streptomyces sp. M41, a bacterium isolated from a South African termite, Macrotermes natalensis. The structures of the complex nonribosomal peptide synthetase-polyketide synthase (NRPS/PKS) hybrid compounds were determined by 1D- and 2D-NMR spectroscopy, high-resolution mass spectrometry, and circular dichroism (CD) spectroscopy. Both cyclic and linear peptides are reported, and the genetic organization of the NRPS modules within the biosynthetic gene cluster accounts for the observed structural diversity...
March 22, 2017: Organic Letters
Tomohiro Morita, Tetsuya Satoh, Masahiro Miura
The rhodium(III)-catalyzed ortho-alkenylation of N-Boc-anilines with alkenes such as acrylate ester and styrene proceeds smoothly through C-H bond cleavage. Obtained o-alkenylanilines can be readily transformed to nitrogen-containing fused heteroaromatic compounds including indoles and quinolines.
March 21, 2017: Organic Letters
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