Browsing by Author "Marazano, Christian"

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    An access to some functionalized azocine derivatives.
    (2000) Gil, Laurent Frédéric; Gil, Rossimiriam Pereira de Freitas; Santos, Daniela Cristina dos; Marazano, Christian
    The syntheses, from readily accessible 3-alkyl-4-methoxy-1,3,4,5-tetrahydropyridine 1, of functionalized 1,6,7,8-tetrahydroazocine 7 and 1,2,7,8-tetrahydroazocine 9 are reported.
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    An enantioselective synthesis of isoquinuclidines from 3-substituted chiral pyridinium salts.
    (2001) Santos, Daniela Cristina dos; Gil, Rossimiriam Pereira de Freitas; Gil, Laurent Frédéric; Marazano, Christian
    A new enantioselective approach to chiral isoquinuclidines, such as 15, 18 and 21, is reported. The key step of these syntheses is a cycloaddition between chiral dihydropyridines 14 or 20, now readily available from tetrahydropyridinium salts 6 or 11, and achiral dienophiles. The reaction proceeds with a very good endo-selectivity and moderate d.e.
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    Microwave-promoted synthesis of chiral pyridinium salts.
    (2005) Viana, Gustavo Henrique Ribeiro; Santos, Itamar Carolino dos; Alves, Rosemeire Brondi; Gil, Laurent Frédéric; Marazano, Christian; Gil, Rossimiriam Pereira de Freitas
    The synthesis of several chiral pyridinium salts via Zincke_s reaction can be easily accomplished by domestic microwave oven irradiation. Yield enhancements, reduction of reaction time, and less racemization were observed under microwave heating when compared to conventional heating in similar conditions.
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    Stereocontrolled alkylation of chiral pyridinium salt toward a short enantioselective access to 2-alkyl- and 2,6-dialkyl-1,2,5,6-tetrahydropyridines.
    (2000) Bertin, Bérangère Guilloteau; Compère, Delphine; Gil, Laurent Frédéric; Marazano, Christian; Das, Bhupesh C.
    Treatment of salts 1a–b with Grignard reagents gives, after reduction of the resulting unstable dihydropyridines 7, the tetrahydropyridines 8a–c, with modest selectivities but in very few steps and under practical conditions. Higher stereoand regioselectivities are obtained with salt 1c which gives the tetrahydropyridines 15a–e. In addition, the dihydropyrid- Introduction The enantioselective synthesis of six-membered nitrogen heterocycles has been the subject of a large number of studies during the past few years due to the interest of these intermediates in natural alkaloid and medicinal chemistry. As a consequence, efficient methods are now available for preparing chiral 2- and 2,6-substituted piperidines.[1] However, few methods are available concerning the corresponding enantiopure substituted tetrahydropyridines.[2] Therefore, we now present a strategy which is briefly summarized in Scheme 1. The main features of this approach are: (a) selective alkylation with Grignard reagents[3–5] of pyridinium salts 1 (Scheme 1), now readily available from chiral primary amines;[6] (b) protonation of the resulting dihydropyridines 2 to give dihydropyridinium salt equivalents 3;[7] (c) additional treatment with a Grignard reagent affording the 2,6-disubstituted tetrahydropyridines 4. Scheme 1. General strategy for the enantioselective construction of substituted tetrahydropyridines The interest of this approach is illustrated by the short synthesis from salt 1c (Scheme 2) of (2)-lupetidin, (1)- solenopsin A and indolizidines (2)-5 and (2)-6, this last synthesis being designed as an example of further ring elaboration of the tetrahydropyridines 4. [a] Institut de Chimie des Substances Naturelles, C.N.R.S. Avenue de la Terrasse, 91198 Gif-Sur-Yvette CEDEX, France Fax: (internat.) 1 33-1/69077247 E-mail: marazano@icsn.cnrs-gif.fr [b] Departamento de Quimica, ICEB, Universidad Federal de Ouro Preto, Campus Morro de Cruzeiro, 35400.00, Ouro Preto, MG, Brazil Eur. J. Org. Chem. 2000, 139121399 Ó WILEY-VCH VerlagGmbH, D-69451Weinheim, 2000 14342193X/00/040821391 $ 17.501.50/0 1391 ine intermediates 11b cyclize to give the new oxazolidine derivatives 12a–e, which turn out to be good precursors of the 2,6-trans-disubstituted tetrahydropyridines 21a–e. Selective syntheses of (–)-lupetidin, (+)-solenopsin, and indolizidines (–)-5 and (–)-6 are presented as representative examples of applications.
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    Synthesis of new azocine derivatives and their functionalization by nucleophilic addition to their iminium salts.
    (2005) Trindade, Angela Cristina Leal Badaró; Santos, Daniela Cristina dos; Gil, Laurent Frédéric; Marazano, Christian; Gil, Rossimiriam Pereira de Freitas
    A route to the eight-membered nitrogen heterocycles 20a,b is described starting from the 3-alkyl-N-benzylpyridinium salts 14a,b. These azocine derivatives were converted into their respective iminium salts 11 by treatment with methanesulfonic acid. A study concerning the regioselectivity of nucleophilic additions to these salts is presented. Nucleophiles like Introduction Azocine derivatives are an important and diverse class of compounds that are found in a range of natural and nonnatural products. These eight-membered nitrogen heterocycles are present in complex structures of many natural substances such apparicine (1),[1] magallanesine (2),[2] and manzamine A (3),[3] an important antitumoral marine alkaloid (Figure 1). Among the nonnatural products, the more commonly found azocines are substituted and fully or partly reduced. These compounds have found application as therapeutic agents in view of their various biological properties, for example as antimalarials, antitussives, nasal decongestants, antihypertensives, and analgesics.[4] Another large and much-studied class of compounds containing the azocine ring is synthetic benzofuroazocines (4), which, due their structure close to that of hypnoanalgesics, possess important activity in the central nervous system (CNS).[5] Finally, these monocyclic medium rings have also found use as synthetic intermediates, for example, in the synthesis of the pyrrolizidine ring system,[6] and they constitute important medium-size cycles in conformational studies. [a] Departamento de Química, ICEx, UFMG Av. Antônio Carlos, 6627, Belo Horizonte, MG, Brazil Fax: +55-031-3499-5700 E-mail: rossi@ciclope.lcc.ufmg.br [b] Departamento de Farmácia, SCS, UFPR, Av. Pref. Lothário Meissner, 3400, Jd. Botânico, Curitiba, PR, Brazil [c] Departamento de Química, ICEB, UFOP, Campus Morro do Cruzeiro, Ouro Preto, MG, Brazil [d] Institut de Chimie des Substances Naturelles, Avenue de la Terrasse, 91198, Gif-sur-Yvette, France © 2005 Wiley-VCH Verlag GmbH & Co. 1052 KGaA, Weinheim DOI: 10.1002/ejoc.200400728 Eur. J. Org. Chem. 2005, 1052–1057 hydride or Grignard reagents react selectively in the 2-position to give adducts such as 22 and 23, while azide and phenylthiolate attack the 6-position to give 24 and 25, respectively.