- Activating Imides with Triflic Acid: A General Intramolecular Aldol Condensation Strategy Toward Indolizidine, Quinolizidine, and Valmerin Alkaloids
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A simple, inexpensive, step economic, and highly modular synthetic strategy to access izidine alkaloids is described. The key step is a TfOH-promoted intramolecular aldol condensation between enol and cyclic imide moieties. This cyclization strategy can be employed within an aza-Robinson annulation framework and represents a general tool to build fused bicyclic amines. To illustrate the power of this method, we describe the preparation of (±)-coniceine, (±)-quinolizidine, (±)-tashiromine, (±)-epilupinine, and the core of (±)-valmerins.
- Quevedo-Acosta, Yovanny,Jurberg, Igor D.,Gamba-Sánchez, Diego
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supporting information
p. 239 - 243
(2020/01/02)
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- Palladium-Catalyzed Dearomative Cyclocarbonylation by C-N Bond Activation
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A fundamentally novel approach to bioactive quinolizinones is based on the palladium-catalyzed intramolecular cyclocarbonylation of allylamines. [Pd(Xantphos)I2], which features a very large bite angle, has been found to facilitate the rapid carbonylation of azaarene-substituted allylamines into bioactive quinolizinones in good to excellent yields. This transformation represents the first dearomative carbonylation and is proposed to proceed by palladium-catalyzed C-N bond activation, dearomatization, CO insertion, and a Heck reaction.
- Yu, Hui,Zhang, Guoying,Huang, Hanmin
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p. 10912 - 10916
(2015/09/15)
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- Reductive transformations of unsaturated azabicyclic nitrolactams
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Using different reducing methods unsaturated indolizidine and quinolizidine lactams substituted with a nitro group were transformed into various alkaloid-like derivatives. Hydrogen transfer and palladium catalyzed hydrogenation gave compounds of ketolactam or lactam type meanwhile the nitro group was eliminated. On the other hand, in presence of Raney-nickel catalyst the nitro compounds were reduced to diastereomeric amino derivatives whose stereochemistry was elucidated by NMR spectroscopy. Using sodium bis-dimethoxy-ethoxy-aluminum-hydride (Red-Al) as reducing agent an unexpected tricyclic azetidine was isolated and characterized.
- Pilipecz, Mihály Viktor,Varga, Tamás Róbert,Scheiber, Pál,Mucsi, Zoltán,Fàvre-Mourgues, Amélie,Boros, Sándor,Balázs, László,Tóth, Gábor,Nemes, Péter
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p. 5547 - 5553
(2012/09/07)
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- Synthesis and transformations of sulfur-substituted indolizidines and quinolizidines
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3-Sulfolenes 1a-b underwent [4+2] cycloaddition reactions with p-toluenesulfonyl isocyanate to give tetrahydropyridinones 3a-b. Through N-detosylation of 3a-b and subsequent intramolecular cyclization, indolizidine 5a and quinolizidine 5b were synthesized
- Chou, Shang-Shing P.,Ho, Chung-Wen
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p. 8551 - 8554
(2007/10/03)
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- Rearrangements of bicyclic nitrones to lactams: Comparison of photochemical and modified barton conditions
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The rearrangement of nitrones to lactams can be carried out by photochemical activation or by treatment with Tf2O followed by KOH-promoted rearrangement (a modification of conditions originally introduced by Barton). Substrates in which the nit
- Zeng, Yibin,Smith, Brenton T.,Hershberger, John,Aube, Jeffrey
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p. 8065 - 8067
(2007/10/03)
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- Intramolecular Schmidt reactions of alkyl azides with ketones: Scope and stereochemical studies
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The intramolecular Schmidt reaction of alkyl azides and ketones has been demonstrated. The reaction is proposed to occur via initial attack of an azide on a ketone activated by a variety of protic or Lewis acids, including trifluoroacetic acid, titanium tetrachloride, and others. The resulting azidohydrin undergoes a direct rearrangement to afford the product amide and molecular nitrogen. When cyclic ketones are used, fused bicyclic lactams of types encountered in a wide variety of natural products are obtained. Although the distance allowed between the carbonyl group and the alkyl azide is quite restricted, the reaction is general with respect to the ketone component, including acyclic ketones and cyclic substrates ranging from standard to large ring sizes. The reaction also succeeds with aldehydes, although elimination or hydride migration products compete. In several cases examined the reaction was found to proceed with retention of configuration at the migrating carbon. Competing reactions with β-diketones and α,β-unsaturated ketones were found to predominate over ring expansion.
- Milligan, Gregory L.,Mossman, Craig J.,Aubé, Jeffrey
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p. 10449 - 10459
(2007/10/03)
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- Syntheses of nitrogen heterocycles by means of amine-directed carbonylation and hydrocarbonylation
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Amine-directed carbonylation of 2-allylpiperidine (5) gives 8-methyl-1-azabicyclononan-9-one (7) with extremely high regio- and stereoselectivity, which is promoted by a stoichiometric amount of 2 in the presence of hydrogen chloride.A c
- Zhang, Zhaoda,Ojima, Iwao
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p. 281 - 289
(2007/10/02)
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- Amide-directed hydrocarbonylation of N-alkenylamides and α-alkenyllactams
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The amide-directed Rh-catalyzed hydroformylation and Pd-catalyzed hydroesterification of N-allylamides give the iso-aldehyde and ester, respectively, with good regioselectivity.The Rh- and Co2Rh2(CO)12-catalyzed reactions of N-methallylamide give an 1-acyl-2-formylpyrrolidine through a novel double carbonylation and an 1-acylpyrrolidine through reductive annulation, respectively, with excellent selectivity.A cyclic hemiamidal, N-benzoyl-2-hydroxy-4-methylpyrrolidine, the key intermediate for the double carbonylation and the reductive annulation, is obtained selectively in a Rh4(CO)12-catalyzed reaction of N-methallylamide.The hydrocarbonylations of this cyclic hemiamidal catalyzed by RhCl(PPh3)3, Co2Rh2(CO)12, and Co2(CO)8 give the corresponding double carbonylation product (2-formylpyrrolidine), reductive annulation product (pyrrolidine), and amidocarbonylation product (proline), respectively, in excellent yield and selectivity.The mechanisms of the novel double carbonylation and the reductive annulation is studied on the basis of deuterium-labeling experiments, and it is found that these reactions proceed via enamide intermediate followed by extremely regioseletive metal hydride addition to the enamide.The Rh-catalyzed hydrocarbonylations of the α-methallyl-γ- and δ-lactams in triethyl orthoformate followed by treatment with TFA give the corresponding 1-azabicycloalkenones via bicyclic hemiamidals through annulation in excellent overall yields.The Co2Rh2(CO)12-catalyzed reactions of these α-methallyl lactams give the corresponding 1-azabicycloalkanones as the sole isolable products in high yields.The RhCl(PPh3)3-catalyzed hydrocarbonylation of 6-allylpiperidin-2-one givesa mixture of 1-azabicyclo and 1-azabicyclo products.However, the addition of phosphines to the Rh catalyst remarkably improves the normal selectivity (n/iso = 9) to give 1-azabicyclodec-2-en-10-one as the predominant product.
- Ojima, Iwao,Zhang, Zhaoda
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p. 253 - 276
(2007/10/02)
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- Hypervalent Organoiodine Reagents in the Transannular Functionalisation of Medium-sized Lactams: Synthesis of 1-Azabicyclo Compounds
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The amidyl radical intermediates, produced by photolysis of medium-sized lactams 7-heptanelactam (1), 8-octanelactam (3), and 9-nonanelactam (6) in the presence of (diacetoxyiodo)benzene (DIB) and iodine, undergo transannular hydrogen abstraction to afford intramolecularly functionalised compounds such as oxoindolizidines (4) and (5) and the 1-azabicyclodecan-2-one (7) that are obtained in high yield from lactams (3) and (6), respectively.
- Dorta, R. L.,Francisco, C. G.,Suarez, E.
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p. 1168 - 1169
(2007/10/02)
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- Bicyclization of aza-compounds by positive halide ions. II. Lactams and some related cyclizations
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Anodic oxidation of lactams in the presence of halide ions produced excellent yields of bicyclic compounds with reactants having rings in the range of eight to ten atoms (C7 to C9).Smaller rings did not react to form bicyclic products and larger rings gave reduced yields.Attempts were made to cyclize non-cyclic amides and to bicyclize cycloheptyl and cyclooctyl acetamide with limited success.
- Elofson, Richard M.,Gadallah, Fahmi F.,Laidler, James K.
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p. 2770 - 2773
(2007/10/02)
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- A CONVENIENT SYNTHESIS OF 1-AZABICYCLOALKANES AND THEIR LACTAMS VIA CUPRATES OF FORMAMIDINES
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Piperidine and pyrrolidine formamidines, transformed into their α-metalloderivatives are alkylated with bifunctional electrophiles and cyclized, on formamidine removal, to the title compounds.
- Edwards, Philip D.,Meyers, A. I.
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p. 939 - 942
(2007/10/02)
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