28,563 results match your criteria Organic Letters [Journal]


Organocatalyzed Aerobic Oxidation of Aldehydes to Acids.

Org Lett 2019 Feb 14. Epub 2019 Feb 14.

Department of Chemistry , University of Science and Technology of China , Hefei , Anhui 230026 , China.

The first example organocatalyzed aerobic oxidation of aldehydes to carboxylic acids in both organic solvent and water under mild conditions is developed. As low as 5 mol % N-hydroxyphthalimide was used as the organocatalyst, and molecular O was used as the sole oxidant. No transition metals or hazardous oxidants or cocatalysts were involved. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00101DOI Listing
February 2019

Rh(III)-Catalyzed Synthesis of 3-Amino-4-arylisoquinolinones from 4-Diazoisochroman-3-imines and N-Methoxybenzamides.

Org Lett 2019 Feb 14. Epub 2019 Feb 14.

Department of Chemistry , Zhejiang University , Hangzhou 310027 , P.R. China.

A Rh(III)-catalyzed reaction of N-methoxybenzamides and 4-diazoisochroman-3-imines is described. This method offers a rapid entry to 3-amino-4-arylisoquinolinone architectures from readily available starting materials under mild reaction conditions. A one-pot cascade C-H bond activation/formal [4 + 2] cycloaddition mechanism is proposed. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00290DOI Listing
February 2019

Palladium-Catalyzed Methylation of Aryl, Heteroaryl, and Vinyl Boronate Esters.

Org Lett 2019 Feb 14. Epub 2019 Feb 14.

Department of Chemistry , University of California , Berkeley , California 94720 , United States.

A method for the direct methylation of aryl, heteroaryl, and vinyl boronate esters is reported, involving the reaction of iodomethane with aryl-, heteroaryl-, and vinylboronate esters catalyzed by palladium and PtBuMe. This transformation occurs with a remarkably broad scope and is suitable for late-stage derivatization of biologically active compounds via the boronate esters. The unique capabilities of this method are demonstrated by combining carbon-boron bond-forming reactions with palladium-catalyzed methylation in a tandem transformation. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00025DOI Listing
February 2019

Ligase-Controlled Cyclo-oligomerization of Peptides.

Org Lett 2019 Feb 14. Epub 2019 Feb 14.

School of Biological Sciences , Nanyang Technological University , 60 Nanyang Drive , Singapore 637551.

A biomimetic one-step ligase-catalyzed cyclo-oligomerization mediated by butelase 1, an Asn/Asp-specific ligase, is introduced that is time-, concentration-, length-, and sequence-dependent. This reaction yields cyclic mono-, di-, tri-, and tetramers from peptide precursors containing 3-15 amino acids ended with Asn and a His-Val tail. The cyclomonomers were favored when the peptide lengths were >9 amino acids. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00151DOI Listing
February 2019

Elucidation of the Herbicidin Tailoring Pathway Offers Insights into Its Structural Diversity.

Org Lett 2019 Feb 14. Epub 2019 Feb 14.

State Key Laboratory of Bio-organic and Natural Products Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry , University of Chinese Academy of Sciences (CAS), CAS, Shanghai 200032 , China.

The biosynthetic gene clusters for herbicidins ( hbc) and aureonuclemycin ( anm) were identified in Streptomyces sp. KIB-027 and Streptomyces aureus, respectively. The roles of genes possibly involved in post-core-assembly steps in herbicidin biosynthesis in these clusters and a related her cluster were studied. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00066DOI Listing
February 2019

Aerobic Oxidation of in Situ Generated Cyanine Dyes Leading to DNA Damage.

Org Lett 2019 Feb 14. Epub 2019 Feb 14.

Center for Photochemical Sciences and Chemistry Department , Bowling Green State University , Bowling Green , Ohio 43403 , United States.

DNA damage induced by noncatalytic aerobic oxidation of pyridinocyanine dyes is described. The dyes are generated in situ during spontaneous oxidations of tetrakis- and bis( N-methylpyridin-4-ium)alkane salts. The mechanism of aerobic oxidation of the latter compound is proposed, and a rare direct catalyst-free transition from saturated alkane to a gem-diol is demonstrated. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00194DOI Listing
February 2019

Synthesis of Dibenzophospholes by TfO-Mediated Intramolecular Phospha-Friedel-Crafts-Type Reaction.

Org Lett 2019 Feb 14. Epub 2019 Feb 14.

Department of Applied Chemistry, Graduate School of Engineering , Osaka University , Suita , Osaka 565-0871 , Japan.

A TfO-mediated intramolecular phospha-Friedel-Crafts-type reaction of secondary biarylphosphine oxides has been developed. The reaction is promoted simply by TfO to form the corresponding dibenzophospholes under metal-free conditions. The starting substrates are readily available and easy-to-handle phosphine oxides, and the regioselectivity is controlled by the innate electronic nature. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00219DOI Listing
February 2019

Photochemically Produced Aminocyclobutanes as Masked Dienes in Thermal Electrocyclic Cascade Reactions.

Org Lett 2019 Feb 14. Epub 2019 Feb 14.

School of Chemistry , University of Bristol , Cantock's Close , Bristol , BS8 1TS , U.K.

Cyclobutane products of a triplet sensitized enamide-alkene intramolecular [2 + 2] photocycloaddition have been shown to undergo fragmentation under acidic conditions. This lability has been exploited by inducing a complexity-generating thermal electrocyclic cascade sequence involving the in situ formation of a cyclobutene, followed by electrocyclic ring opening, Diels-Alder cycloaddition, and subsequent lactamization. This combination of excited state photochemistry and thermal electrocyclic cascade reactions allows simple planar molecules to be rapidly transformed into sp-rich scaffolds. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00211DOI Listing
February 2019

Aerobic Oxidative Alkenylation of Weak O-Coordinating Arylacetamides with Alkenes via a Rh(III)-Catalyzed C-H Activation.

Org Lett 2019 Feb 14. Epub 2019 Feb 14.

Department of Chemistry , Indian Institute of Technology Madras , Chennai 600036 , Tamil Nadu , India.

A versatile and site-selective rhodium(III)-catalyzed aerobic oxidative alkenylation of arylacetamides including primary, secondary, and tertiary amides having a weak O-coordinating acetamide directing group with alkenes is described. In the reaction, air was utilized as a sole oxidant. The reaction was compatible with activated alkenes and maleimides. Read More

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http://dx.doi.org/10.1021/acs.orglett.8b04140DOI Listing
February 2019

Hemisquaramide Tweezers as Organocatalysts: Synthesis of Cyclic Carbonates from Epoxides and CO.

Org Lett 2019 Feb 14. Epub 2019 Feb 14.

Division of Applied Chemistry, Graduate School of Natural Science and Technology , Okayama University , Tsushima, Okayama 700-8530 , Japan.

Hemisquaramide tweezers, a new family of H-bond donor organocatalysts, are reported. The catalysts could be synthesized within two steps. Among them, H-binaphthyl-linked hemisquaramide 7 markedly accelerated the synthesis of cyclic carbonates from epoxides and CO. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00117DOI Listing
February 2019

Complexity and Diversity Generation in the Biosynthesis of Fumiquinazoline-Related Peptidyl Alkaloids.

Org Lett 2019 Feb 14. Epub 2019 Feb 14.

State Key Laboratory of Bioactive Substance and Function of Natural Medicines , Institute of Materia Medica, Chinese Academy of Medical Sciences & Peking Union Medical College , Beijing 100050 , P.R. China.

Fumiquinazolines are multicyclic peptidyl alkaloids where FAD-dependent oxidases are main tailing redox enzymes in their biosynthesis. Here, we characterized the use of an α-KG/Fe(II)-dependent dioxygenase (α-KGD) as a new strategy in Nature to increase structural complexity in fumiquinazolines biosynthesis by elucidating the concise three enzymes biosynthetic pathway of heptacyclical alanditrypinone (1). Further genome mining led to the discovery of additional gene cluster with α-KGD and trimodular NRPS as partner, which generates diverse fumiquinazolines. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00260DOI Listing
February 2019

Diagonally π-Extended Perylene-Based Bis(heteroacene) for Chiroptical Activity and Integrating Luminescence with Carrier-Transporting Capability.

Org Lett 2019 Feb 14. Epub 2019 Feb 14.

State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering , Hunan University , Changsha 410082 , P. R. China.

We report the synthesis and characterization of a novel bis(heteroacene), in which four benzothiophene units diagonally fused to a twisted perylene and spatially arranged in a double helical-like structure. The described compound yielded chiroptically active atropisomers with a perfect CD response and furthermore circularly polarized luminescence with a g of ∼1.09 × 10. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00152DOI Listing
February 2019

DNA-Compatible [3 + 2] Nitrone-Olefin Cycloaddition Suitable for DEL Syntheses.

Org Lett 2019 Feb 14. Epub 2019 Feb 14.

Department of Chemistry and Chemical Biology , Harvard University , 12 Oxford Street , Cambridge , Massachusetts 02138 , United States.

The limited scope of DNA-compatible chemistry restricts the types of chemical features that can be incorporated into DNA-encoded libraries (DELs). Here, a method to synthesize DNA-conjugated polycyclic isoxazolidines via a [3 + 2] nitrone-olefin cycloaddition is described. The reaction is compatible with many olefin-containing substrates and diverse N-alkylhydroxylamines. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00017DOI Listing
February 2019

Nitration-Peroxidation of Alkenes: A Selective Approach to β-Peroxyl Nitroalkanes.

Org Lett 2019 Feb 13. Epub 2019 Feb 13.

Department of Chemistry , Renmin University of China , Beijing 100872 , China.

Nitration-peroxidation of alkenes for the synthesis of β-peroxyl nitroalkanes has been developed by using tert-butyl nitrite and tert-butyl hydroperoxide. The method presents a new and selective difunctionalization of alkenes to introduce a nitro group and a peroxyl group across the double bonds of alkenes under mild conditions. A radical reaction pathway is proposed by experimental and theoretical studies. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00266DOI Listing
February 2019

Rh(II)/Brønsted Acid Catalyzed General and Highly Diastereo- and Enantioselective Propargylation of in Situ Generated Oxonium Ylides and C-Alkynyl N-Boc N,O-Acetals: Synthesis of Polyfunctional Propargylamines.

Org Lett 2019 Feb 13. Epub 2019 Feb 13.

Key Laboratory of Medicinal Chemistry for Natural Resource, Ministry of Education, School of Chemical Science and Technology , Yunnan University , Kunming 650091 , China.

The first metal/organo cooperatively catalyzed asymmetric reaction of C-alkynyl N-Boc-protected N,O-acetals with in situ generated oxonium ylides has been developed. This new type of propargylation allows for the efficient synthesis of structurally diverse unreported chiral propargylamines bearing oxa-quaternary stereocenters. The reaction features unprecedented substrate scope and high diastereo- and enantioselectivity. Read More

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http://dx.doi.org/10.1021/acs.orglett.8b04051DOI Listing
February 2019

Alstonlarsines A-D, Four Rearranged Indole Alkaloids from Alstonia scholaris.

Org Lett 2019 Feb 13. Epub 2019 Feb 13.

State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering , Lanzhou University , Lanzhou 730000 , People's Republic of China.

Four indole alkaloids, alstonlarsines A-D (1-4), were isolated from Alstonia scholaris and structurally characterized. Compound 1 possesses a new carbon skeleton with a cage-shaped 9-azatricyclo[4.3. Read More

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http://pubs.acs.org/doi/10.1021/acs.orglett.9b00230
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http://dx.doi.org/10.1021/acs.orglett.9b00230DOI Listing
February 2019
2 Reads

Perhydrolysis in Ethereal HO Mediated by MoO(acac): Distinct Chemoselectivity between Ketones, Ketals, and Epoxides.

Org Lett 2019 Feb 12. Epub 2019 Feb 12.

State Key Laboratory of Bioorganic and Natural Products Chemistry, Center for Excellence in Molecular Synthesis , Shanghai Institute of Organic Chemistry and the University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road , Shanghai 200032 , China.

Ketones, ketals, and epoxides were converted into corresponding hydroperoxides in high yields by reaction with ethereal HO in the presence of a catalytic amount of MoO(acac) with distinct (to date unattainable) chemoselectivity. Read More

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http://pubs.acs.org/doi/10.1021/acs.orglett.9b00425
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http://dx.doi.org/10.1021/acs.orglett.9b00425DOI Listing
February 2019
4 Reads

Synthesis of 2-(2-Oxo-2-phenylethyl)cyclopentanone by Rhodium-Catalyzed Tandem Alkynyl Cyclobutanols Hydroacylation and Semipinacol Rearrangement.

Org Lett 2019 Feb 12. Epub 2019 Feb 12.

State Key Laboratory of Organometallic Chemistry , Shanghai Institute of Organic Chemistry , Center for Excellence in Molecular Synthesis, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road , Shanghai 200032 , P. R. China.

A rhodium-catalyzed tandem reaction of alkynyl cyclobutanols with salicylaldehydes has been developed. The reaction offers a new and atom-economical approach for the selective preparation of multisubstituted 2-(2-oxo-2-phenylethyl)cyclopentanone in high yields under mild reaction conditions with tolerance of a broad range of substituted alkynyl cyclobutanols and salicylaldehyes. The isolation of intermediate suggests that the reaction proceeds through a sequential process of intermolecular hydroacylation and semipinacol rearrangement. Read More

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http://pubs.acs.org/doi/10.1021/acs.orglett.8b03973
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http://dx.doi.org/10.1021/acs.orglett.8b03973DOI Listing
February 2019
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Copper-Catalyzed Aminoboration from Hydrazones To Generate Borylated Pyrazoles.

Org Lett 2019 Feb 12. Epub 2019 Feb 12.

Department of Chemistry , University of California, Irvine , Irvine , California 92697-2025 , United States.

Herein we report an aminoboration reaction that employs inexpensive, Earth-abundant, and commercially available Cu(OTf) as an effective catalyst in the direct addition of B-N σ bonds to C-C π bonds, generating borylated pyrazoles, which are useful building blocks for drug discovery. By nature of the mechanism, the reaction produces exclusively one regioisomer and tolerates groups incompatible with alternative lithiation/borylation and iridium-catalyzed C-H activation/borylation methods. The reaction can be scaled up, and the resulting isolable pyrazole pinacol boronates can be further functionalized through palladium-catalyzed Suzuki cross-coupling reactions. Read More

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http://pubs.acs.org/doi/10.1021/acs.orglett.8b04038
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http://dx.doi.org/10.1021/acs.orglett.8b04038DOI Listing
February 2019
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Multicomponent Synthesis of Isoindolinones by Rh Relay Catalysis: Synthesis of Pagoclone and Pazinaclone from Benzaldehyde.

Org Lett 2019 Feb 12. Epub 2019 Feb 12.

Key Laboratory of the Ministry of Education for Advanced Catalysis Materials , Zhejiang Normal University , 688 Yingbin Road , Jinhua 321004 , China.

A practical one-pot isoindolinone synthesis enabled by Rh catalysis was developed. The advantage of this protocol is that it does not require pre-preparation of amide substrates, because Rh participates in two reactions independently. This mild, operationally multicomponent process transforms a wide variety of commercially available aldehydes into the corresponding γ-lactams in good yields, thereby demonstrating that N-pyridin-2-yl benzamide is an effective directing group. Read More

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http://dx.doi.org/10.1021/acs.orglett.8b04026DOI Listing
February 2019

Asymmetric Transfer Hydrogenation of Heterobicyclic Alkenes with Water as Hydrogen Source.

Org Lett 2019 Feb 12. Epub 2019 Feb 12.

YMU-HKBU Joint Laboratory of Traditional Natural Medicine , Yunnan Minzu University , Kunming 650500 , China.

The asymmetric transfer hydrogenation of heterobicyclic alkenes was accomplished by using water as the sole hydrogen source. The transformation was co-catalyzed by Pd(OAc)/Zn(OTf) dual catalyst with metallic zinc as reducing agent. Various azabenzonorbornadienes and oxabenzonorbornadienes were transformed to the corresponding chiral 1,2-dihydronaphthalenes by the asymmetric reductive ring-opening reactions with good to excellent enantioselectivities. Read More

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http://pubs.acs.org/doi/10.1021/acs.orglett.9b00059
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http://dx.doi.org/10.1021/acs.orglett.9b00059DOI Listing
February 2019
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Iodine(III)-Catalyzed Electrophilic Nitration of Phenols via Non-Brønsted Acidic NO Generation.

Org Lett 2019 Feb 12. Epub 2019 Feb 12.

Department of Chemistry, Graduate School of Sciences , Kyoto University , Sakyo, Kyoto 606-8502 , Japan.

The first catalytic procedure for the electrophilic nitration of phenols was developed using iodosylbenzene as an organocatalyst based on iodine(III) and aluminum nitrate as a nitro group source. This atom-economic protocol occurs under mild, non-Brønsted acidic and open-flask reaction conditions with a broad functional-group tolerance including several heterocycles. Density functional theory (DFT) calculations at the (SMD:MeCN)Mo8-HX/(LANLo8+f,6-311+G*) level indicated that the reaction proceeds through a cationic pathway that efficiently generates the NO ion, which is the nitrating species under neutral conditions. Read More

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http://dx.doi.org/10.1021/acs.orglett.8b04141DOI Listing
February 2019

Site-Selective and Enantioselective α,β,γ-Functionalization of 5-Alkylidenefuran-2(5 H)-ones: A Route to Polycyclic γ-Lactones.

Org Lett 2019 Feb 12. Epub 2019 Feb 12.

Institute of Organic Chemistry , Lodz University of Technology , Żeromskiego 116 , 90-924 Łódź , Poland.

A new strategy for a direct α,β,γ-functionalization of the γ-lactone framework in the corresponding 5-alkylidenefuran-2(5 H)-ones is reported. The developed approach is based on a stereocontrolled cascade reaction with 2-mercaptocarbonyl compounds proceeding in a sequence of thia-Michael/aldol/oxa-Michael reactions. Such a synthetic strategy allows for a construction of a unique polycyclic architecture containing γ-lactone, tetrahydrofuran, and tetrahydrothiophene ring systems. Read More

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http://dx.doi.org/10.1021/acs.orglett.8b03796DOI Listing
February 2019

Genome Mining of Streptomyces atratus SCSIO ZH16: Discovery of Atratumycin and Identification of Its Biosynthetic Gene Cluster.

Org Lett 2019 Feb 12. Epub 2019 Feb 12.

CAS Key Laboratory of Tropical Marine Bio-resources and Ecology, Guangdong Key Laboratory of Marine Materia Medica, RNAM Center for Marine Microbiology , South China Sea Institute of Oceanology, Chinese Academy of Sciences , Guangzhou 510301 , China.

Genome mining of the deep sea-derived Streptomyces atratus SCSIO ZH16 enabled the activation of a cyclodepsipeptide gene cluster and isolation of its cinnamic acid-bearing product, atratumycin (1). Atratumycin's structure was elucidated on the basis of extensive spectroscopic experiments, X-ray data, and Marfey's method; a plausible biosynthesis and tailoring modification of 1 are also proposed and investigated. Additionally, atratumycin is active against Mycobacteria tuberculosis H37Ra and H37Rv with MICs of 3. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00208DOI Listing
February 2019

In Situ Activation of Disulfides for Multicomponent Reactions with Isocyanides and a Broad Range of Nucleophiles.

Org Lett 2019 Feb 11. Epub 2019 Feb 11.

College of Chemistry and Chemical Engineering , Shanghai University of Engineering Science 333 Longteng Road , Shanghai 201620 , China.

Activation of disulfides with N-halogen succinimide in the presence of TEMPO allows insertion reaction by an isocyanide, the product of which can further accept a wide range of nucleophiles for the generation of isothioureas and related molecular moieties. This new procedure overcomes previous methods that accept essentially only aryl amines as the third nucleophilic component. The diverse nucleophiles usable in our new protocol make this approach a general method for de novo synthesis of many S-containing heterocycles. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00275DOI Listing
February 2019

Synthesis of Amino-Substituted α- and δ-Carbolines via Metal-Free [2 + 2 + 2] Cycloaddition of Functionalized Alkyne-Nitriles with Ynamides.

Org Lett 2019 Feb 8. Epub 2019 Feb 8.

Collaborative Innovation Center of New Drug Research and Safety Evaluation, Henan Province, Key Laboratory of Advanced Drug Preparation Technologies, Ministry of Education, School of Pharmaceutical Sciences, and College of Chemistry and Molecular Engineering , Zhengzhou University , Zhengzhou , Henan 450001 , P. R. China.

A metal-free [2 + 2 + 2] cycloaddition of alkyne-cyanamides or ynamide-nitriles with ynamides is described for the efficient synthesis of amino-substituted α- and δ-carbolines. This novel methodology is environmentally friendly and allows for highly regioselective access to carboline derivatives in good to excellent yields with wide functional group tolerance. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00021DOI Listing
February 2019

1,4-Palladium Shift/C(sp)-H Activation Strategy for the Remote Construction of Five-Membered Rings.

Org Lett 2019 Feb 8. Epub 2019 Feb 8.

University of Basel , Department of Chemistry , St. Johanns-Ring 19 , CH-4056 Basel , Switzerland.

1, n-Metal shift is an elegant alternative approach enabling the functionalization of remote C-H bonds from simple precursors. In this work, we report a novel and simple Pd-catalyzed domino reaction involving 1,4-palladium shift and C(sp)-H activation and leading to (fused) five-membered rings. This method allowed access to a broad range of valuable arylidene γ-lactams and indanones and was applied to the formal synthesis of (-)-pyrrolam. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00187DOI Listing
February 2019

Cystobactamids 920-1 and 920-2: Assignment of the Constitution and Relative Configuration by Total Synthesis.

Org Lett 2019 Feb 8. Epub 2019 Feb 8.

Institut für Organische Chemie und Biomolekulares Wirkstoffzentrum (BMWZ) der Leibniz Universität Hannover , Schneiderberg 1B , 30167 Hannover , Germany.

Total synthesis of cystobactamid 920-1 and its epimer has allowed an unambiguous assignment of the relative and absolute configuration of the natural product. A careful structural analysis of each isomer using both NMR and computational techniques also prompted a constitutional revision of the structures originally reported for cystobactamids 920-1 and 920-2, and has provided further insight into the unique conformational preferences of the cystobactamid family. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00058DOI Listing
February 2019

Photoinduced Transition-Metal-Free Cross-Coupling of Aryl Halides with H-Phosphonates.

Org Lett 2019 Feb 8. Epub 2019 Feb 8.

The State Key Laboratory of Applied Organic Chemistry , Lanzhou University , 222 Tianshui Road , Lanzhou 730000 , People's Republic of China.

Photoinduced transition-metal- and photosensitizer-free cross-coupling of aryl halides (including Ar-Cl, Ar-Br, and Ar-I) with H-phosphonates (including dialkyl phosphonates and diarylphosphine oxides) is reported. Various functional groups were tolerated, including ester, methoxy, dimethoxy, alkyl, phenyl, trifluoromethyl, and heterocyclic compounds. This simple and green strategy provides a practical pathway to synthesize arylphosphine oxides. Read More

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http://pubs.acs.org/doi/10.1021/acs.orglett.8b04081
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http://dx.doi.org/10.1021/acs.orglett.8b04081DOI Listing
February 2019
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Hydrogen-Bond-Controlled Formal Meta-Selective C-H Transformations and Regioselective Synthesis of Multisubstituted Aromatic Compounds.

Org Lett 2019 Feb 8. Epub 2019 Feb 8.

Institute for Materials Chemistry and Engineering , Kyushu University , 6-1 Kasugakoen , Kasuga-shi , Fukuoka 816-8580 , Japan.

The meta-selective introduction of functional groups into aromatic substrates was successfully achieved by hydrogen-bond-controlled meta-selective C-H borylation and successive conversion of the boryl group to other functional groups. By this method a wide range of functional groups could be introduced without isolation of the borylated intermediates. The desired meta-functionalized aromatic products were obtained in a one-pot manner even on a gram scale. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00030DOI Listing
February 2019

Discovery and Heterologous Biosynthesis of the Burnettramic Acids: Rare PKS-NRPS-Derived Bolaamphiphilic Pyrrolizidinediones from an Australian Fungus, Aspergillus burnettii.

Org Lett 2019 Feb 8. Epub 2019 Feb 8.

Department of Molecular Sciences , Macquarie University , Sydney , New South Wales 2109 , Australia.

The burnettramic acids are a new class of antibiotics from an Australian fungus Aspergillus burnettii. The rare bolaamphiphilic scaffold consists of β-d-mannose linked to a pyrrolizidinedione unit via a 26-carbon chain. The most abundant metabolite displayed potent in vitro antifungal activity. Read More

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http://dx.doi.org/10.1021/acs.orglett.8b04042DOI Listing
February 2019

Electrochemical Aminoselenation and Oxyselenation of Styrenes with Hydrogen Evolution.

Org Lett 2019 Feb 8. Epub 2019 Feb 8.

College of Chemistry , Nanchang University , Nanchang 330031 , Jiangxi , P.R. China.

The use of additive-free conditions is an ideal approach to prepare organoselenium reagents from readily available unsaturated substrates. Thus, we report the electro-induced aminoselenation and oxyselenation of styrenes without any acids or oxidants as additives. This transformation is compatible with various functional groups, which leads to vicinal difunctionalized organoselenium compounds. Read More

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http://dx.doi.org/10.1021/acs.orglett.8b03274DOI Listing
February 2019

Minnamide A, a Linear Lipopeptide from the Marine Cyanobacterium Okeania hirsuta.

Org Lett 2019 Feb 7. Epub 2019 Feb 7.

Department of Chemistry , Keio University , 3-14-1, Hiyoshi , Kohoku-ku, Yokohama , Kanagawa 223-8522 , Japan.

Minnamide A is a lipopeptide with a unique repeating structure consisting of hydroxy and proposed β-branched methyl groups. The absolute configuration of minnamide A was determined by a combination of chemical degradation, chiral HPLC analyses, and synthetic methods. Minnamide A showed growth-inhibitory activity toward HeLa cells with an IC value of 0. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00135DOI Listing
February 2019

Iridium-Catalyzed Benzylamine C-H Alkenylation Enabled by Pentafluorobenzoyl as the Directing Group.

Org Lett 2019 Feb 7. Epub 2019 Feb 7.

Key Laboratory of Green Chemistry & Technology, Ministry of Education College of Chemistry , Sichuan University Chengdu 610064 , P.R. China.

The first iridium-catalyzed oxidative alkeynylation of benzylamines with acrylates enabled by a new directing group pentafluorobenzoyl has been developed. The reaction proceeded efficiently in the presence of silver acetate as oxidant and chlorobenzene as solvent. A good range of benzylamines could be selectively monoalkenylated without interfering with further aza-Michael addition. Read More

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http://dx.doi.org/10.1021/acs.orglett.8b04005DOI Listing
February 2019

Critical Role of Achiral Guest Molecules in Planar Chirality Inversion of Alanine-Appended Pillar[5]arenes.

Org Lett 2019 Feb 7. Epub 2019 Feb 7.

Department of Chemistry and Research Institute of Natural Sciences Gyeongsang National University , Jinju 52828 , Korea.

Planar chirality inversion of pillar[5]arenes bearing d- or l-alanine substituents on both rims was investigated upon addition of guest molecules having pyridinium or imidazole moieties and long alkyl chains. The d- and l-alanine-substituted pillar[5]arenes exhibited pS and pR planar chirality, respectively. However, this planar chirality was inverted upon inclusion of certain achiral molecules, comprising pyridinium or imidazole moieties and long alkyl chains with terminal hydroxyl or methyl groups. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00277DOI Listing
February 2019
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(+)- and (-)-Preuisolactone A: A Pair of Caged Norsesquiterpenoidal Enantiomers with a Tricyclo[4.4.0.0]decane Carbon Skeleton from the Endophytic Fungus Preussia isomera.

Org Lett 2019 Feb 7. Epub 2019 Feb 7.

Graduate School of Pharmaceutical Sciences , The University of Tokyo , Bunkyo-ku, Tokyo 113-0033 , Japan.

A pair of enantiomeric norsesquiterpenoids, (+)- and (-)-preuisolactone A (1) [(+)-1 and (-)-1)] featuring an unprecedented tricyclo[4.4.0. Read More

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http://dx.doi.org/10.1021/acs.orglett.8b04123DOI Listing
February 2019

aza-Wittig Reaction with Nitriles: How Carbonyl Function Switches from Reacting to Activating.

Org Lett 2019 Feb 7. Epub 2019 Feb 7.

Department of Chemistry , Lomonosov Moscow State University , Leninskie gory 1-3 , Moscow 119991 , Russia.

Transformations of α-EWG-substituted (electron-withdrawing group, EWG) γ-azidobutyronitriles proceeding via unusual aza-Wittig reactions between the phosphazene and nitrile functions and affording pyrrole-derived iminophosphazenes were developed. α-EWGs were found to control chemoselectivity and, depending on their nature, act as CN group activators (e.g. Read More

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http://dx.doi.org/10.1021/acs.orglett.8b04135DOI Listing
February 2019
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Amichalasines A-C: Three Cytochalasan Heterotrimers from Aspergillus micronesiensis PG-1.

Org Lett 2019 Feb 7. Epub 2019 Feb 7.

Hubei Key Laboratory of Natural Medicinal Chemistry and Resource Evaluation, School of Pharmacy, Tongji Medical College , Huazhong University of Science and Technology , Wuhan 430030 , China.

Amichalasines A-C (1-3), which represent a new type of cytochalasan heterotrimers, were isolated from Aspergillus micronesiensis PG-1. Compounds 1 and 2 possess an undecacyclic 5/6/11/5/5/6/6/5/11/6/5 ring system, and 3 has an additional furan ring with a dodecacyclic 5/6/11/5/5/6/6/5/5/11/6/5 ring system. 1 and 2 exhibited potent cytotoxic activities through apoptosis induction mediated by caspase-3 activation and PARP degradation, and their IC values against HL60 cells were 1. Read More

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http://pubs.acs.org/doi/10.1021/acs.orglett.8b04066
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http://dx.doi.org/10.1021/acs.orglett.8b04066DOI Listing
February 2019
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Catalyst-Free, Direct Electrochemical Tri- and Difluoroalkylation/Cyclization: Access to Functionalized Oxindoles and Quinolinones.

Org Lett 2019 Feb 7. Epub 2019 Feb 7.

Institut für Organische und Biomolekulare Chemie , Georg-August-Universität , Tammannstraße 2 , 37077 Göttingen , Germany.

The catalyst-free electrochemical di- and trifluoromethylation/cyclization of N-substituted acrylamides was realized under external oxidant-free conditions. The strategy provides expedient access to fluoroalkylated oxindoles and 3,4-dihydroquinolin-2(1 H)-ones with ample scope and broad functional group tolerance by mild, direct electrolysis of sodium sulfinates in an undivided cell. Detailed mechanistic studies provided strong support for a SET-based reaction manifold. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00361DOI Listing
February 2019
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Palladium-Catalyzed Oxidative Allylation of Sulfoxonium Ylides: Regioselective Synthesis of Conjugated Dienones.

Org Lett 2019 Feb 6. Epub 2019 Feb 6.

Key Laboratory of Functional Molecular Engineering of Guangdong Province, Guangdong Engineering Research Center for Green Fine Chemicals, School of Chemistry and Chemical Engineering , South China University of Technology , Guangzhou 510640 , P. R. China.

The first examples of palladium-catalyzed allylic C-H oxidative allylation of sulfoxonium ylides to afford the corresponding conjugated dienones with moderate to good yields have been established. The features of this novel conversion include mild reaction conditions, wide substrate scope, and excellent regioselectivity. Read More

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http://dx.doi.org/10.1021/acs.orglett.8b03606DOI Listing
February 2019

Cytorhizins A-D, Four Highly Structure-Combined Benzophenones from the Endophytic Fungus Cytospora rhizophorae.

Org Lett 2019 Feb 6. Epub 2019 Feb 6.

State Key Laboratory of Applied Microbiology Southern China, Guangdong Provincial Key Laboratory of Microbial Culture Collection and Application, Guangdong Open Laboratory of Applied Microbiology , Guangdong Institute of Microbiology , Guangzhou 510070 , China.

Cytorhizins A-D, four novel polyketide heterodimers, were isolated from the endophytic fungus Cytospora rhizophorae A761. These new compounds shared an unprecedented 6/6/5/6/8 or 6/6/5/6/7 pentacyclic ring system and fused as a fascinating cagelike skeleton, embodying by a polyoxygenated isopentyl unit and a highly structure-combined benzophenone scaffold. Their structures were elucidated by extensive spectroscopic analyses and X-ray diffraction techniques. Read More

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http://dx.doi.org/10.1021/acs.orglett.8b04107DOI Listing
February 2019
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Enantioselective Total Synthesis of (-)-Δ-Tetrahydrocannabinol via N-Heterocyclic Carbene Catalysis.

Org Lett 2019 Feb 6. Epub 2019 Feb 6.

School of Chemistry , Monash University , Clayton , Victoria 3800 , Australia.

Enantioselective syntheses of (-)-Δ-tetrahydrocannabinol ((-)-Δ-THC) and (-)-Δ-THC have been achieved in eight and 10 steps, respectively, from a known cinnamic acid. The syntheses take advantage of an enantioselective N-heterocyclic carbene (NHC)-catalyzed (4 + 2) annulation between donor-acceptor cyclobutanes and cinnamoyl fluorides to construct the highly enantioenriched cycloxyl β-lactone shown. Having constructed this A-ring precursor, elaboration to (-)-Δ-THC is achieved through β-lactone alcoholysis followed by oxidation, dual decarboxylation, trimethylation, and cationic cyclization. Read More

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http://pubs.acs.org/doi/10.1021/acs.orglett.9b00198
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http://dx.doi.org/10.1021/acs.orglett.9b00198DOI Listing
February 2019
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Photosensitized, Energy-Transfer-Mediated Cyclization of 2-(1-Arylvinyl)benzaldehydes to Anthracen-9-(10 H)-ones.

Org Lett 2019 Feb 6. Epub 2019 Feb 6.

Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences , Nanyang Technological University , Singapore 637371 , Singapore.

A visible-light-induced photocatalytic intramolecular cyclization of 2-(1-arylvinyl)benzaldehydes is reported. The reaction is promoted in the presence of an Ir photocatalyst and an amine base at room temperature under the irradiation of blue LEDs, affording 10-methylanthracen-9(10 H)-one derivatives in moderate to good yields with tolerance to various functional groups. A series of mechanistic experiments suggest that the reaction proceeds via energy transfer from the excited Ir photocatalyst to the substrate to generate a diradical, which then undergoes 1,5-hydrogen shift, 6π electrocyclization, and aromatization leading to the cyclic product. Read More

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http://dx.doi.org/10.1021/acs.orglett.9b00182DOI Listing
February 2019

Formal [4 + 2] Cycloadditions of Anhydrides and α,β-Unsaturated N-Tosyl Ketimines.

Org Lett 2019 Feb 5. Epub 2019 Feb 5.

Department of Chemistry , University of California , One Shields Ave , Davis , California 95616 , United States.

A method for the diastereoselective synthesis of highly substituted β-enamino ketones from anhydrides and ketone-derived imines is reported. Cyclic, enolizable anhydrides undergo a base-promoted conjugate addition reaction with α,β-unsaturated N-tosyl ketimines, followed by an intramolecular acylation to give formal [4 + 2] cycloaddition products. The carboxylic acid-containing products are formed with modest selectivity for the cis-diastereomer and can be fully epimerized to the trans-diastereomer upon esterification. Read More

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http://pubs.acs.org/doi/10.1021/acs.orglett.8b04091
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http://dx.doi.org/10.1021/acs.orglett.8b04091DOI Listing
February 2019
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Synthesis of Chiral α-Aminosilanes through Palladium-Catalyzed Asymmetric Hydrogenation of Silylimines.

Org Lett 2019 Feb 5. Epub 2019 Feb 5.

The asymmetric hydrogenation of silylimines was first developed by using a palladium complex of a P-stereogenic diphosphine ligand as the catalyst, affording the valuable chiral α-aminosilanes with quantitative conversions and excellent enantioselectivities (up to 99% ee). Read More

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http://dx.doi.org/10.1021/acs.orglett.8b04073DOI Listing
February 2019
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Hydride Transfer Involved Redox-Neutral Cascade Cyclizations for Construction of Spirocyclic Bisoxindoles Featuring a [3,4]-Fused Oxindole Moiety.

Org Lett 2019 Feb 5. Epub 2019 Feb 5.

College of Chemistry and Pharmaceutical Sciences , Qingdao Agricultural University , Qingdao 266109 , China.

The hydride transfer involved redox-neutral cascade cyclization has been developed to construct the spirocyclic bisoxindoles featuring a [3,4]-fused oxindole moiety from rationally designed C4-amine-substituted isatins, affording the diverse tricyclic [3,4]-fused oxindoles with three consecutive chiral centers in good yields and excellent diastereoselectivities (>20:1). Read More

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http://pubs.acs.org/doi/10.1021/acs.orglett.8b04100
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http://dx.doi.org/10.1021/acs.orglett.8b04100DOI Listing
February 2019
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Site-Selective and Stereoselective C-H Functionalization of N-Cyclopropylamides via a Directed Remote Metalation Strategy.

Org Lett 2019 Feb 4. Epub 2019 Feb 4.

Department of Chemistry and Biotechnology, School of Science , Tallinn University of Technology , Tallinn 12618 , Estonia.

A new methodology for site-selective and stereoselective C-H functionalization of aminocyclopropanes via directed remote lithiation has been developed. Treatment of N-directing group (DG = pivaloyl, tetramethylsuccinimidoyl) arylcyclopropanes with t-BuLi results in a clean β-lithiation and, following quench with electrophiles, leads to a range of cyclopropane derivatives. Sequential double lithiation-methylation to give a dimethylated cyclopropane has been achieved. Read More

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http://dx.doi.org/10.1021/acs.orglett.8b03955DOI Listing
February 2019

Mechanistic Insight into the Catalytic Staudinger Ligation.

Org Lett 2019 Feb 4. Epub 2019 Feb 4.

Institute for Molecules and Materials , Radboud University , Heyendaalseweg 135 , 6525 AJ Nijmegen , The Netherlands.

Organophosphorus-catalyzed Staudinger ligation between carboxylic acids and azides in the presence of phenylsilane reductant produces amides. NMR-based mechanistic investigations revealed that the catalytic Staudinger ligation does not proceed via reduction of phosphine oxide but rather via reduction of iminophosphorane, which can subsequently undergo several transformations to produce the amide product. Read More

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http://pubs.acs.org/doi/10.1021/acs.orglett.8b04035
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http://dx.doi.org/10.1021/acs.orglett.8b04035DOI Listing
February 2019
2 Reads