Showing papers on "Annulation published in 1988"
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01 Jan 1988
TL;DR: Robinson Annelation Aldol Condensation Cyclization by Michael and Aldol Combination, Claisen and Dieckmann Reactions Intramolecular Alkylation Cationic Cyclization Diels$Alder Reactions Other Thermal Processes Radical Cyclization Synthesis of Small-Ring Compounds Ring Expansion and Contraction Transitory Annelations as mentioned in this paper.
Abstract: Robinson Annelation Aldol Condensation Cyclization by Michael and Aldol Combination, Claisen, and Dieckmann Reactions Intramolecular Alkylation Cationic Cyclization Diels$Alder Reactions Other Thermal Processes Radical Cyclization Synthesis of Small-Ring Compounds Ring Expansion and Contraction Transitory Annelation.
66 citations
64 citations
TL;DR: In this article, a general procedure for cyclopentane synthesis based on free-radical cyclization of thioacetals is described, which permits the rapid assembly of various ring systems bearing useful functionality for use in total synthesis.
61 citations
TL;DR: In this article, the dehydrobromination of (Z)-2-bromovinyl silyl ethers has been employed in the first synthesis of trialkylsilyloxyethyne derivatives.
54 citations
TL;DR: The enaminoester 1-benzyl-2-(ethoxycarbonylmethylene)-imidazolidine undergoes N-acylation and conjugate C-addition with α,β-unsaturated acyl imidazolides to afford imidazo[1,2- a ]pyridones.
49 citations
TL;DR: Cycloaddition d'azido-8 oxo-6 octadiene-2,4oate de methyle en hydroxy-4 aza-1bicyclo [3.1.0] hexaneacrylate-6 of methyle que l'on transforme ensuite en oxo 7 pyrrolizinecarboxylates-1
Abstract: Cycloaddition d'azido-8 oxo-6 octadiene-2,4oate de methyle en hydroxy-4 aza-1bicyclo [3.1.0] hexaneacrylate-6 de methyle que l'on transforme ensuite en oxo-7 pyrrolizinecarboxylates-1
46 citations
TL;DR: In this article, a new cyclopentenone annulation reaction was developed, which involves the in situ epoxidation [tBuOOH, VO(acac)2] of vinyl allenes 1a-f in 40~70% yield.
44 citations
TL;DR: A synyhesis protocol involving beta-lithiation of 2-(2-pyridinyl)indoles (4 → 5) and subsequent reaction with bromoacetaldehyde leads to the indol[2,3-a]quinolzine(1) ring system.
44 citations
TL;DR: The total synthesis of retigeranic acid 1 was achieved in 14 steps from menthene as mentioned in this paper, with the key features involved the vinylcyclopropanation of enone 6 with the dienolate anion of 5 to furnish Vinylcyclopropane 4 and its rearrangement to pentacycle 3 in an overall cyclopentene annulation sequence.
43 citations
TL;DR: The aza-Wittig reaction of iminophosphoranes derived from N-substituted o-azidobenzamides or 2-(o-azido) phenyl benzimidazole with isocyanates, carbon dioxide or carbon disulphide, lead to functionalized 4(3H)-quinazolinones and benziminidazo [1,2-c]quinazolines respectively.
43 citations
TL;DR: Methylene-cyclopentane and -cyclohexane derivatives were synthesized by the reaction of 2-methylene-propane-1,3-diol diacetate with dicarbanions under the palladium catalysis as mentioned in this paper.
TL;DR: In this paper, the B-ring of daunomycinone is formed by reaction of 3-(methoxycarbonyl)-5-hexynoate 1 with the naphthyl carbene complexes 4/5.
Abstract: Tetracarbonyl-Chelat-Carben-Komplexe des Chroms 4, 5 und 18 reagieren mit terminalen Alkinen unter regiospezifischer Anellierung der Carbenliganden zu Schlusselprodukten der Anthracyclinon-Synthese. Aus 3-(Methoxycarbonyl)-5-hexinsaureester 1 und den Naphthylcarben-Komplexen 4/5 wird der B-Ring des Daunomycinons aufgebaut. Das Metall wird aus den Anthracenol-Komplexen 6/7 unter CO-Druck als Hexacarbonylchrom zuruckgewonnen. Konventionelle Schritte fuhren zum Tetracyclus 14/15, der als Vorstufe des Daunomycinons C und dessen 4-Demethoxy-Analogon dient. Die Anellierung des Anisyl-Komplexes 18 durch die Propargylcyclohexandione 16/17 liefert unter Aufbau des C-Rings nach Ruckgewinnung des Metalls die Naphthol-Derivate 21/22. Schlusselschritte zum tetracyclischen Diketon 25, einer bekannten Vorstufe des 11-Deoxydaunomycinons E, sind die Kettenverlangerung des Ketones 23 mit Isocyanmethyl-p-tolylsulfon zur Carbonsaure 24 und deren Cyclisierung mit TFA/TFAA.
carbene Ligands as Anthracyclinone Synthons, 61). — Metal Carbene Chelates as key Reagents in Syntheses of the Daunomycinone Series: Regiospecific Annulation of Arylcarbene Ligands as a Strategy towards the Synthesis of Rings B and C
Reaction of tetracarbonyl carbene chelates of chromium 4, 5, and 18 with terminal alkynes leads to regiospecific annulation of the carbene ligands to give key intermediates in anthracyclinone synthesis. The B-ring of daunomycinone is formed by reaction of 3-(methoxycarbonyl)-5-hexynoate 1 with the naphthylcarbene complexes 4/5. The metal is recycled as hexacarbonylchromium by decomplexation of the anthracenol complexes 6/7 under CO pressure. Conventional steps lead to the tetracyclic systems 14/15 which serve as precursors to daunomycinone C and its 4-demethoxy analogue. The synthesis of ring C involves the annulation of the anisyl complex 18 by the propargylcyclohexanediones 16/17, and — after cleavage of the metal — leads to the naphthol derivatives 21/22. The functionalization of the ketone 23 to give the acid 24 via isocyanomethyl p-tolyl sulfone and the cyclization using TFA/TFAA are key steps towards the tetracyclic diketone 25 which is a well-known precursor of 11-deoxydaunomycinone E.
TL;DR: In this article, annulation of carbo- or heteroaromatic rings at the 1 2 positions can activate 3-cyanoindolizines as 1,3-dipolar species.
TL;DR: In this paper, a number of useful annulation methods were developed and these annulation sequences played key roles in effecting total syntheses of the sesquiter-penoids (+)-axamide-1 and (+)-axisisonitrile-1, the diterpenoid (+)-(14S)- dolasta-1(15),7,9-trien-l4-ol, and the sesterterpenoid (2)-palauolide.
Abstract: The preparation and synthetic uses of a number of bifunctional reagents (5-chloro-2-trimethylstannyl-2-pentene and related substances, (~)-1-bromo-4-methyl-3-trimethylstannyl-2-pentene, and alkyl (z)- and (~)-2,3-bis(trimethylstannyl)-2-alkenoates) are described. In this work a number of useful annulation methods were developed and these annulation sequences played key roles in effecting total syntheses of the sesquiter- penoids (+)-axamide-1 and (+)-axisonitrile-1, the diterpenoid (+)-(14S)- dolasta-1(15),7,9-trien-l4-ol, and the sesterterpenoid (2)-palauolide. A versatile synthesis of functionalized, stereochemically defined tetra- substituted alkenes, starting from cr,j3-acetylenic esters, has been developed.
TL;DR: In this paper, a general approach to the synthesis of iridoid aglycones is reported, where a combination of Claisen rearrangement/nitrile oxide cycloaddition sequence has permitted the facile annulation of a highly functionalized cyclopentane ring onto a simple glycal derived from D-xylal.
TL;DR: The reaction of amines with 2,3-diphenylsulfonyl-1, 3-butadiene produces 3-pyrrolines which are readily oxidized to 3-phenyl sulfonyl pyrroles as mentioned in this paper.
TL;DR: The first direct annelation to the 1,2,4-triazine ring based on the diaddition of bifunctional nucleophiles at C-5 and C-6 was reported in this article.
TL;DR: The title compound 1 has been synthesized from diol 3a, either directly or after protection of the two hydroxy groups as benzyl ethers, by an intramolecular Pauson-Khand bis-annulation, followed by catalytic hydrogenation and oxidation in overall yields ranging from 15% (free diol) to 35% (dibenzyl ether) as discussed by the authors.
TL;DR: In this paper, a new strategy for the synthesis of five, six, and seven-membered rings by use of novel allyl-silane reagents is described, and preliminary details of this strategy are discussed.
TL;DR: In this article, the iodo ketones were treated with n-butyllithium in tetrahydrofuran (THF) at low temperatures and the cis-fused bicyclic alcohols were converted into bicyclic tertiary alcohols.
TL;DR: The use of cerium (III) chloride alters the chemoselectivity of the reaction of the Grignard reagent with ester-acetals and also greatly improves the efficiency of reaction with lactones as discussed by the authors.