Enaminones: versatile intermediates for natural product synthesis*
30 Jun 1999-Pure and Applied Chemistry (International Union of Pure and Applied Chemistry)-Vol. 71, Iss: 6, pp 979-988
TL;DR: In this article, an overview of the chemistry of enaminones and related compounds containing the structural unit N-CaC-Z (Za COR, CO2R, CN, NO2, S O 2Ar, etc.).
Abstract: Efforts in our laboratories to devise a general approach to the synthesis of alkaloids focus on the versatile reactivity of enaminones and related compounds containing the structural unit N-CaC-Z (Za COR, CO2R, CN, NO2 ,S O 2Ar, etc.). This lecture presents an overview of our research with these useful building blocks. Themes to be elaborated include chemo- selectivity and diastereoselectivity in reactions of enaminones, and the challenge of controlling absolute stereochemistry.
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TL;DR: In this paper, the title compound, 3-(4-(phenylamino)phenylmoylamino)-cyclohex-2-enone, β-enaminone, was synthesized by the treatment of 1,3-cycloenanedione with p-amino diphenylamine and its crystal structure determined.
Abstract: The title compound, 3-(4-(phenylamino)phenylamino)cyclohex-2-enone, β-enaminone of 1,3-cyclohexanedione and p-amino diphenylamine (C18H18N2O) was prepared and characterized by 1H-NMR, 13C-NMR, Elemental analysis and IR spectroscopy as well as single crystal X-ray diffraction. These results indicate the predominance of the keto-enol tautomerism. Molecular conformation around the central disubstituted benzene ring is affected by the tautomerism and two steric effects between side molecular groups and mono substituted benzene ring. Electron delocalizations due to these effects have been observed in the molecular structure, the structure being stabilized by some intermolecular hydrogen bonds. The title compound, 3-(4-(phenylamino)phenylamino)cyclohex-2-enone, was synthesized by the treatment of 1,3-cyclohexanedione with p-amino diphenylamine and its crystal structure determined. According to 1H and 13C NMR data the newly prepared β-enaminone compound exists as the E-s-E-s-Z conformation. This is consistent with X-ray crystallographic study.
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TL;DR: Two synthetic pathways to substituted hexahydroimidazo[1,2-a]pyridines, which may serve as precursors ofaza-alkaloids, were investigated in this paper.
Abstract: Department of Chemistry, Eastern Michigan University, Ypsilanti, Michigan 48179, USAReceived July 28, 2008Two synthetic pathways to substituted hexahydroimidazo[1,2-a]pyridines, which may serve as precursors ofaza-alkaloids, were investigated. The first involves the condensation of a bisnucleophilic enediaminoester anda biselectrophile. The second involves attachment to nitrogen of the carbon chain skeleton required to form thesix-memberd ring, before formation of the enediaminoester. Several substituted hexahydroimidazo[1,2-a]pyridines were synthesized via these two approaches.Key Words : Aza-alkaloid, Heterocyclic compounds, IndolizidineIntroductionAlkaloids are naturally occurring organic compoundscontaining nitrogen atoms. Many alkaloids have importantand unique pharmacological activities. Alkaloids have beenisolated not only from well known sources such as plants ornative drugs but also from animals, insects, marine organisms,and microorganisms. Examples of well known alkaloidsinclude morphine, nicotine, cocaine, and quinine. Thealkaloids which are related to this research are izidinealkaloids
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TL;DR: In this article, a wide range of N-(ethoxycarbonylmethyl)enaminones, prepared by the Eschenmoser sulfide contraction between N(ethoxy carbonyl methyl)pyrrolidine-2-thione and various bromomethyl aryl and hetero-aryl ketones, underwent cyclization in the presence of silica gel to give ethyl 6-(hetero)aryl-2,3-dihydro-1H-Pyrrolizine-5-carboxylates within minutes
Abstract: A wide range of N-(ethoxycarbonylmethyl)enaminones, prepared by the Eschenmoser sulfide contraction between N-(ethoxycarbonylmethyl)pyrrolidine-2-thione and various bromomethyl aryl and heteroaryl ketones, underwent cyclization in the presence of silica gel to give ethyl 6-(hetero)aryl-2,3-dihydro-1H-pyrrolizine-5-carboxylates within minutes upon microwave heating in xylene at 150 °C. Instead of functioning as a nucleophile, the enaminone acted as an electrophile at its carbonyl group during the cyclization. Yields of the bicyclic products were generally above 75%. The analogous microwave-assisted reaction to produce ethyl 2-aryl-5,6,7,8-tetrahydroindolizine-3-carboxylates from (E)-ethyl 2-[2-(2-oxo-2-arylethylidene)piperidin-1-yl]acetates failed in nonpolar solvents, but occurred in ethanol at lower temperature and microwave power, although requiring much longer time. A possible mechanism for the cyclization is presented, and further functionalization of the newly created pyrrole ring in the dihydropyrrolizine core is described.
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TL;DR: In the title compound, C21H17NO, the phenyl ring directly linked to the carbonyl group is oriented at an angle of 7.3 (2)° with respect to the aniline ring.
Abstract: In the title compound, C21H17NO, the phenyl ring directly linked to the carbonyl group is oriented at an angle of 7.3 (2)° with respect to the aniline ring, and at an angle of 55.6 (2)° with respect to the other phenyl ring. There is an intramolecular hydrogen bond involving the NH group and the carbonyl O atom. The crystal structure is stabilized by weak C—H⋯π interactions, which link the molecules into a herringbone arrangement.
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Cites methods from "Enaminones: versatile intermediates..."
...It is therefore not surprising that many synthetic methods have been developed for the preparation of these compounds (Greenhill, 1977; Michael et al., 1999; Elassar & El-Khair, 2003)....
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TL;DR: In this article, an effective one-pot, multicomponent, and solvent-free reaction for conjugated enaminones containing three alkyl carboxylate groups was described.
Abstract: An effective, one-pot, multicomponent, and solvent-free reaction for synthesis of conjugated enaminones containing three alkyl carboxylate groups is described. The reaction of primary amine, alkyl acetoacetate, and dialkyl acetylenedicarboxylate obtained the title compound in good yields in a short time.
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References
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01 Jan 1991
TL;DR: In this paper, the total synthesis of amaryllidaceae alkaloids has been studied using radical cyclization reactions in total syntheses of naturally occurring indole alkaloid.
Abstract: Chapter headings. Carbon-13 and proton NMR shift assignments and physical constants of diterpenoid alkaloids. Supercritical fluid extraction of alkaloids. Recent advances in the total synthesis of amaryllidaceae alkaloids. Applications of radical cyclization reactions in total syntheses of naturally occurring indole alkaloids.
1,263 citations
Book•
29 Jun 1993
TL;DR: This paper presents the first total Synthesis of several Natural Products Based On Alkyne-Co2(Co2)6 Complexes, and discusses the design and synthesis of Cooperative "Pinwheel" Fluorescent Sensors, and the application of Silicon-Ass Intramolecular Cross-Coupling.
Abstract: Chapter 1. The Total Synthesis Of Luzopeptins. Chapter 2. Synthesis of Geldanamycin Using Glycolate Aldol Reactions. Chapter 3. From Methylene Bridged Glycoluril Dimers To Cucurbit[N]Uril Analogs With Some Detours Along The Way. Chapter 4. Application Of Silicon-Assisted Intramolecular Cross-Coupling In Total Synthesis Of (+)-Brasilenyne. Chapter 5. Samarium(II) Promoted Ketyl Olefin Cyclizations Applied To The Total Syntheses Of (-)-Steganone And (+)-Isoschizandrin. Chapter 6. The Synthesis Of Polycavernoside A. An Example Of Conformationally Guided Macrolactonization. Chapter 7. First Total Synthesis Of Several Natural Products Based On Alkyne-Co2(Co)6 Complexes. Chapter 8. Total Synthesis Of Myriaporones 1, 3, and 4. Chapter 9. Adventures In Natural Product Synthesis: From Deep Sea Sponge To Pilot Plant. The Large Scale Total Synthesis Of The Marine Natural Product (+)-Discodermolide. Chapter 10. Synthesis Of Aprepitant. Chapter 11. Total Synthesis And Mechanism Of Action Studies On The Antitumor Alkaloid,(-)-Agelastatin A. Chapter 12. Design And Synthesis of Cooperative "Pinwheel" Fluorescent Sensors. Chapter 13. Functionalization Of Pyridines And Thiazoles Via The Halogen-Dance Reaction, Application To The Total Synthesis Of Caerulomycin C And WS75624 B. Chapter 14. Diastereoselective Intramolecular 4+3 Cycloaddition And An Enantioselective Total Synthesis Of (+)-Dactylol.
175 citations
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