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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

AbstractEfforts 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. more

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Abstract: Enaminoketones and esters are gaining increased interest, particularly cyclic-β-enaminoesters, which are known as important intermediates for the synthesis of heterocycles and natural products, because the enantioselective preparation of highly functionalized compounds is of central importance in synthetic chemistry. Enaminones are versatile synthetic intermediates that combine the ambident nucleophilicity of enamines with the ambident eletrophilicity of enones. Enaminoketones and enaminonitriles have proven to be versatile building blocks for the synthesis of various heterocycles such as pyridine, pyrimidine and pyrrole derivatives. Enaminones systems have "enone" character, and may act as acceptors in both 1,2 and 1,4-additions. In this way the enaminone serves as a scaffold for annulation, and can gain access to systems such as pyrroles indolizidines, quinolizidines and perhydroindoles, all of which are common motifs in alkaloid structures. Enaminones are frequently employed as building blocks for the preparation of a variety of bicyclic compounds of biological interest and have been recently recognized as potential anticonvulsant compounds. Since a large number of developments in the use of enaminones in heterocyclic synthesis have occurred, a review of the recent developments in the synthetic approaches, covering the literature since 1995 until 2004, to these interesting molecules and their useful chemical transformations and biological activity can be considered of considerable value.

150 citations

Journal ArticleDOI
Abstract: A variety of β-enamino ketones and esters have been synthesized in high to exellent yields by reacting β-dicarbonyl compounds with amines in the presence of a catalytic amount of indium tribromide. The reaction proceeds smoothly at room temperature in a short reaction time under solvent-free conditions.

117 citations

Journal ArticleDOI
Abstract: Bismuth(III) trifluoroacetate has been found to be an extremely efficient catalyst for the preparation of β-enaminones in water. In addition, by employing this catalyst, high regio- and chemoselective enamination of carbonyl compounds was achieved.

106 citations

Journal ArticleDOI
TL;DR: Although disguised as a 6-endo-dig cyclization, the reagents employed in the transformation play a direct role in bond making and bond breaking, thus changing the mode of addition.
Abstract: A new reaction for the preparation of enaminones has been discovered. This method employs β-amino acids as starting materials to allow diversification as well as incorporation of chirality. The β-amino acids, once converted to ynones, are readily cyclized to the desired six-membered enaminone via a two-step, one-pot protocol. Although disguised as a 6-endo-dig cyclization, the reagents employed in the transformation play a direct role in bond making and bond breaking, thus changing the mode of addition.

80 citations

Journal ArticleDOI
Abstract: A convenient synthesis of 5-oxo-1,2,3,5-tetrahydropyrrolo[1,2- a ]quinoline-4-carboxylic acids, tricyclic analogues of the quinolone antibiotics, is described. Key steps in the route are a novel zinc-mediated Reformatsky reaction between diethyl bromomalonate and N -arylpyrrolidine-2-thiones 18 , and cyclisation of the resulting diethyl pyrrolidinylidenemalonate intermediates 19 in polyphosphoric acid. The products proved to be devoid of biological activity.

77 citations

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01 Jan 1991
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.

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