Showing papers on "Annulation published in 1986"
TL;DR: In this paper, the power of cycloadditions for ring formation derives from the potential for chemo-, regio-, diastereo-, and enantioselectivity, and three types of conjunctive reagents appear to be promising candidates: (1) selected 4-alky-lidene-4,5-dihydro-3H-pyrazoles, (2) 2-[(trimethylsilyl)methyl]allyl esters and halides, and (3) alkylidenecycloprop
Abstract: The power of cycloadditions for ring formation derives from the potential for chemo-, regio-, diastereo-, and enantioselectivity. Trimethylenemethane (TMM) and its equivalents offer the possibility of extending such benefits to the synthesis of five-membered rings. Three types of conjunctive reagents appear to be promising candidates: (1) selected 4-alky-lidene-4,5-dihydro-3H-pyrazoles, (2) 2-[(trimethylsilyl)methyl]allyl esters and halides, and (3) alkylidenecyclopropanes. Thermal reactions, especially intramolecular ones, effect the cycloaddition of the pyrazoles to olefins–especially electron-poor olefins. The latter two precursors require a catalyst, notably a palladium complex, to unlock the synthetic potential. With the 2-[(trimethylsilyl)methyl]allyl esters, a general chemo-, regio-, and diastereoselective cycloaddition with typical Diels-Alder dienophiles forms methylenecyclopentanes in both inter- and intramolecular fashion. A tin analogue allows extension of this cycloaddition to aldehydes, and, in a related sequence, to ketones and imines to form 3-methylenete-trahydrofurans and 3-methylenepyrrolidines with excellent diastereoselectivity. The 2-[(tri-methylsilyl)methyl]allyl esters also serve to effect net methylenecyclopentane annulation to cyclic enols. Such adducts can further undergo three-carbon intercalation or combined ring contraction-spiroannulation simply by the use of either a nucleophilic or electrophilic trigger. Alkylidenecyclopropanes undergo cycloadditions to both electron-rich and electron-poor olefins when stimulated by metal catalysts, especially palladium. A complementary regiochemistry to the approach based upon silicon conjunctive reagents is observed. The availability of these cycloadditions provides new strategies for the synthesis of natural products.
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TL;DR: A short total synthesis of the bacterial coenzyme methoxatin (1) (4,5-dihydro-4, 5-dioxo-1H-pyrrolo[2,3-f]quinoline-2,7,9-tricarboxylic acid) is described in this article.
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TL;DR: In this paper, a unified mechanistic model for the reaction of manganese(III) acetate with carboxylic acids and alkenes is proposed. But the model does not consider the role of α-H acidity of the carboxyl acid component, electron deficient radical additions, metal complexed organic radicals, and the importance of an oxo-centered manganized triangle in the lactone annulation reaction.
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TL;DR: Synthese de tri-, tetra-and pentamethylene-1,6 1H-pyridones-2 a partir de methoxy-2 pyridine et d'ω-[perhydropyrannyl-2oxy] propyl-, -butyl- and -pentyllithiums as discussed by the authors.
Abstract: Synthese de tri-, tetra- et pentamethylene-1,6 1H-pyridones-2 a partir de methoxy-2 pyridine et d'ω-[perhydropyrannyl-2oxy] propyl-, -butyl- et -pentyllithiums
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38 citations
TL;DR: In this paper, 3-amino-5-methyl-(or 5-phenyl)thiophene-2-carbonitriles 7 and 8 were obtained in a single step by conjugate addition of mercaptoacetonitrile (generated in situ) to substituted acetylenic nitriles 4 and 5 and annelation of intermediate vinylic thioethers.
TL;DR: Annelation de R-3 thiophenecarbaldehyde-2, -carboxylate-2 de methyle et -carbonitrile-2 and R-4 thiophen carboxylates-3 de methylene and carbonitrile, avec des accepteurs de Michael: obtention de benzo disubstitues-5,6 as mentioned in this paper.
Abstract: Annelation de R-3 thiophenecarbaldehyde-2, -carboxylate-2 de methyle et -carbonitrile-2 et de R-4 thiophenecarboxylate-3 de methyle et -carbonitrile-3 avec des accepteurs de Michael: obtention de benzo [b] thiophenes disubstitues-5,6 et de leurs derives amino ou hydroxy-7 et d'amino- ou hydroxy-4 benzo [c] thiophenes disubstitues-5,6
TL;DR: In this article, the Kraus method was used to transform 3-cyano-1(3H)-isobenzofuranone into (1R*, 3R*, 4R*)-pyrano-γ-lactones.
Abstract: Reaction of lithiated 3-cyano-1(3H)-isobenzofuranone (7) with 5-substituted 2-furfuralacetones 6a-c and subsequent O-methylation of the resulting naphthohydroquinones afforded 2-acetyl-3-furylnaphthalenes 8a-c in good yields. Annulation of the dialkoxyphthalides 12a, b with 6a could also be carried out to give 13a, b. The 5-tert-butoxy-2-furyl compounds were stereoselectively transformed into (1R*, 3R*, 4R*)-pyrano-γ-lactones 16a, 18a, b in high yields by a modification of the Kraus method (LiAlH4 reduction followed by treatment of the product carbinol with p-toluenesulfonic acid (TsOH) in acetonitrile and then with 1, 8-diazabicyclo[5.4.0]undec-7-ene in toluene at low temperatures). The 5-methoxy-2-furyl compound 9b also afforded 16a stereoselectively in one step (treatment with TsOH), but this compound was less effective as a substrate of the pyrano-γ-lactone annulation since a side reaction leading to the spiro-γ-lactone 17 became significant. The 5-phenylthio compound 9c failed to give 16a under a variety of conditions.
TL;DR: In this article, δ-oxoketendithioacetals derived from acyclic and cyclic ketones are shown to react with benzylmagnesium chloride to give novel naphthoannelated aromatic compounds by sequential 1,4-and 1,2-additions followed by subsequent cycloaromatization of the resulting carbinols.
TL;DR: In this article, a new CC bond was formed and arising of a 5-hexenyl radical, which further undergoes to 5-exo-trigonal cyclization with a cyclopentane ring annulation.
TL;DR: In this paper, three photochemical methods aiming primarily at syntheses of cyclopentanoid natural products are described: (A) the development and synthetic applications of four generations of tricyclooctanone-type key intermediates all products of oxadi-ir-methane rearrangements are reviewed.
Abstract: Three photochemical methods aiming primarily at syntheses of cyclopentanoid natural products are described: (A) The development and synthetic applications of four generations of tricyclooctanone-type key intermediates all products of oxadi-ir-methane rearrangements are reviewed. Most recent achievements are the total syntheses of (-)-5-oxosilphiperfol-6-ene and of (-)-coriolin. (B) The [2+2] photocycloaddition of 2-trimethylsiloxybutadiene to a number of standard enones proved to be quite a general reaction with appreciable yields. This finding is surprising since dienes in general are known to quench enone triplets efficiently and hence suppress chemical reactions. Both the high substrate concentrations, which can be employed in the present procedure, and the remarkable regioand stereocontrol of the addition processes qualify this annulation as a valuable synthetic method. One photoproduct is the point of departure for an expedient assembly of the basic pentalenolactone skeleton. (C) Spirocyclic chiral 1,3-dioxenones, prepared in a one-step procedure, served for highly selective asymmetric [2+2] d. Mayo-type photocycloadditions with various olef ins. The value of this novel method is documented by an exploratory preparative example, a short synthesis of (+)-grandisol.
TL;DR: In this paper, a new annulation process was developed for the efficient synthesis of the bicyclic keto esters 1 and 6, desired intermediates for the total synthesis of bilobalide.
TL;DR: Synthese de R-3 coumarines et des derives methyl-4 par reaction du salicylaldehyde ou dacetophenone, d'un acide carboxylique (R−CH 2 −COOH) and de chlorure de dichlorophosphoryloxymethylene dimethyl ammonium dans le dichloromethane en presence de triethylamine (R=phenyl, phenoxy, benzyl,phenacyl, ethoxycarbonyl) as discussed by the authors.
Abstract: Synthese de R-3 coumarines et des derives methyl-4 par reaction du salicylaldehyde ou d'acetophenone, d'un acide carboxylique (R−CH 2 −COOH) et de chlorure de dichlorophosphoryloxymethylene dimethyl ammonium dans le dichloromethane en presence de triethylamine (R=phenyl, phenoxy, benzyl, phenacyl, ethoxycarbonyl)
TL;DR: In this paper, the sequential ene reaction annelation sequence has been shown to be applicable to 2-and 3- substituted methylenecycloalkanes, and indenone 8a has been prepared from 4a in one pot in 60% yield.
TL;DR: A simple, one pot, stereoconvergent synthesis of spirocycles has been achieved in excellent yield and further studies on one step bifunctional annulating reagents have resulted in the development of a new allylsilane based cyolopentannulation reaction.
TL;DR: An efficient cationic cyclization reaction has been developed to prepare substituted naphthalenes as discussed by the authors, which can be used for the synthesis of polynuclear aromatic hydrocarbons and C-glycosyl anthraquinones.
TL;DR: In this article, the intramolecular cyclopentene annulation methodology was used to synthesize linear tricyclopentanoids of the hirsutane class or nonlinear members of the isocomene class.
Abstract: The intramolecular cyclopentene annulation methodology which combines the cyclopropanation of dienic diazoketones and the vinylcyclopropane rearrangement is utilized to synthesize linear tricyclopentanoids of the hirsutane class or nonlinear members of the isocomene class. The requisite diene precursors, endocyclic or exocyclic, respectively, are obtained from acylcyclopentenes via orthoester Claisen rearrangement of either allyl or propargyl alcohols. The scope and the generality of the method are indicated and experimental details are presented pertaining to the synthesis of precursory dienes for hirsutane and isocomene sesquiterpenes. Full details are disclosed concerning the total synthesis of epiisocomene and the synthesis of linearly fused precursors to coriolin sesquiterpenes.
TL;DR: Two regiospecific consecutive alkylations of carvone at C 4 followed by acid-catalysed cyclisation afford bicyclic ketones which are potential intermediates for the synthesis of several classes of terpenes.
TL;DR: In this article, a two-step annulation method was developed which features stereospecific formation of three contiguous asymmetric centers, and a new, high yield, two step annulation algorithm was developed.