- Expedient pyrrolizidine synthesis by propargylsilane addition to N-acyliminium ions followed by gold-catalyzed α-allenyl amide cyclization
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(Chemical Equation Presented) A reaction sequence, involving the addition of (substituted) propargylsilanes to lactam-derived N-acyliminium ions followed by gold-catalyzed cyclization of the resulting α-allenyl amide, is applied in expedient syntheses of
- Breman, Arjen C.,Dijkink, Jan,Van Maarseveen, Jan H.,Kinderman, Sape S.,Hiemstra, Henk
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supporting information; experimental part
p. 6327 - 6330
(2009/12/24)
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- Reactions of iminium ions with Michael acceptors through a Morita-Baylis-Hillman-type reaction: Enantiocontrol and applications in synthesis
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(Chemical Equation Presented) All adducts one way: Iminium ions, generated in situ from the corresponding N,O-acetals, can be used as electrophiles in a Morita-Baylis-Hillman-type reaction with a wide range of Michael acceptors (enones, enals, S- and O-acrylates). The reaction has been rendered asymmetric using sulfide 1 (see scheme; DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene, TMSOTf=trimethylsilyl trifluoromethanesulfonate).
- Myers, Eddie L.,De Vries, Johannes G.,Aggarwal, Varinder K.
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p. 1893 - 1896
(2008/03/12)
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- Isoechinatine, a pyrrolizidine alkaloid from Cynoglossum furcatum
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The pyrrolizidine alkaloids of Cynoglossum furcatum have been isolated and characterized. They are isoechinatine 1, a new pyrrolizidine ester alkaloid, echinatine, neocoramandaline and a free necine heliotridine. Isoechinatine is formulated as 9-(O)-(+)-viridiflorylheliotridine. 3-Hydroxy 6-methylpyridine has also been isolated and characterized.
- Ravikumar,Lakshmanan
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p. 406 - 409
(2007/10/03)
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- Intramolecular Allylstannane Cyclizations in Alkaloid Synthesis: Applications to Pyrrolizidine Alkaloids
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Syntheses of (+/-)-isoretronecanol, (+/-)-supinidine, (-)-dihydroxyheliotridane, and (+)-heliotridine are detailed.The key step in each case involves an intramolecular acyliminium ion cyclization onto a suitably positioned allylstannane for construction o
- Keck, Gary E.,Cressman, Erik N. K.,Enholm, Eric J.
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p. 4345 - 4349
(2007/10/02)
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- Pyrrolizidine Alkaloid Biosynthesis. Synthesis of 3H-Labelled Trachelanthamidine and Isoretronecanol and their Incorporation into Three Pyrrolizidine Bases (Necines)
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(+/-)-Isoretronecanol (22) and (+/-)-trachelanthamidine (24) were prepared by 1,3-dipolar cycloaddition of N-formylproline with ethyl propiolate followed by reduction steps.These 3H-labelled 1-hydroxymethylpyrrolizidines together with putrescine were fed to Senecio isatideus which produces retrorsine (1); S. pleistocephalus which yields rosmarinine (8); and Cynoglossum officinale which affords echinatine (5).The double labelling experiments demonstrated that isoretronecanol is incorporated much more efficiently into rosmarinine than into retrorsine or echinatine, whereas trachelanthamidine is a much more efficient precursor for retrorsine and echinatine.Base hydrolysis of retrorsine and echinatine labelled with trachelanthamidine and of rosmarinine labelled with isoretronecanol established that most of the 3H-label was in the base portions, retronecine (2), heliotridine (6), and rosmarinecine (9), respectively.Further degradation of retronecine and rosmarinecine showed that most of the radioactivity was confined to the β-alanine (4) portion.The biosynthetic pathways to isoretronecanol and trachelanthamidine apparently diverge prior to the formation of these 1-hydroxymethylpyrrolizidines, probably during the cyclisation of an immonium ion (14) to form the 1-formylpyrrolizidines (15) and (17).
- Kunec, Ellen K.,Robins, David J.
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p. 1437 - 1441
(2007/10/02)
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- AN IMPROVED SYNTHESIS OF (+)-HELIOTRIDINE
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An alternative synthesis of (+)-heliotridine was achieved from 7-hydroxy-1-methylene-hexahydro-3H-pyrrolizin-5-one,through conversion of exo-methylene to allylic alcohol part.
- Kano, Shinzo,Yuasa, Yoko,Shibuya, Shiroshi
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p. 253 - 256
(2007/10/02)
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- Pyrrolizidine Alkaloid Analogues. Synthesis of 11-Membered Macrocyclic Diesters of (+)-Heliotridine
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The first synthesis of macrocyclic diesters incorporating (+)-heliotridine has been achieved.Treatment of (+)-heliotridine (1) with different glutaric anhydride derivatives produced mainly the corresponding 9-monoesters of heliotridine.Lactonisation was carried out after formation of the pyridine-2-thiol esters to give a range of 11-membered macrocyclic diesters of heliotridine.The structures of these new pyrrolizidine alkaloid analogues were established by comparison of their (1)H n.m.r. and mass spectra with those of natural macrocyclic pyrrolizidine alkaloids.Attempts to make 10-membered macrocyclic diesters of heliotridine were unsuccessful.
- Hagan, Desmond B.,Robins, David J.
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p. 1165 - 1168
(2007/10/02)
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- THE SYNTHESIS OF HELIOTRIDINE AND RELATED ALKALOIDS
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An efficient synthesis of heliotridine from readily available retronecine was accomplished by nucleophilic displacement of the 7-mesylate, in the 7-mesyl-9-benzoate of retronecine with various cesium carboxylates in DMF, followed by hydrolysis.The synthet
- Glinski, Jan A.,Zalkow, Leon H.
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p. 2857 - 2860
(2007/10/02)
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- FREE RADICAL CYCLIZATIONS IN ALKALOID SYNTHESIS: (+)-HELIOTRIDINE AND (+)-HASTANECINE
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Treatment of phenylthiolactams 5a-5f with tri-n-butyltin hydride and AIBN affords mixtures of reduction and cyclization products.Cyclization products partition between indolizidinones and pyrrolizidinones depending on the terminal alkyne substituent.When
- Choi, Joong-Kwon,Hart, David J.
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p. 3959 - 3972
(2007/10/02)
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- Synthesis of optically active pyrrolizidinediols: (+)-Heliotridine
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A practical synthesis of the unsaturated pyrrolizidinediol (+)-heliotridine (5) is reported, starting from the readily available (S)-malic acid. The azabicyclo[3.3.0]octane ring system has been constructed via a stereoselective acyliminium ion cyclization directed by an acetoxy substituent. A ketene dithioacetal substituent in the cyclization precursor serves both as an efficient cationic cyclization terminator and later as a means of controlling double bound migration regioselectively into the correct position in the pyrrolizidine skeleton.
- Chamberlin,Chung
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p. 3653 - 3656
(2007/10/02)
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