Showing papers on "Annulation published in 1999"
TL;DR: Fischer-type carbene complexes have received increasing interest as selective reagents in organic synthesis Apart from its electron-acceptor properties exploited in carbene ligand centered reactions, the metal carbonyl fragment provides a template for non-classical cycloaddition reactions as discussed by the authors.
Abstract: Over the past three decades Fischer-type carbene complexes have received increasing interest as selective reagents in organic synthesis Apart from its electron-acceptor properties exploited in carbene ligand centered reactions, the metal carbonyl fragment provides a template for non-classical cycloaddition reactions The most useful among them is the chromium-mediated benzannulation which allows a one-pot access to densely functionalized oxygenated arenes coordinated to a Cr(CO)3 fragment It is compatible with a variety of functional groups, occurs under mild conditions with remarkable chemo-, regio- and diastereoselectivity, and thus has considerable potential in the synthesis of complex targets and natural products
278 citations
TL;DR: 3,4-disubstituted isocoumarins and polysubstituting alpha-pyrones have been prepared in good yields by treating halogen- or triflate-containing aromatic and alpha,beta-unsaturated esters, respectively, with internal alkynes in the presence of a palladium catalyst.
Abstract: A number of 3,4-disubstituted isocoumarins and polysubstituted alpha-pyrones have been prepared in good yields by treating halogen- or triflate-containing aromatic and alpha,beta-unsaturated esters, respectively, with internal alkynes in the presence of a palladium catalyst. Synthetically, the methodology provides an especially simple and convenient, regioselective route to isocoumarins and alpha-pyrones containing aryl, silyl, ester, tert-alkyl, and other hindered groups. The reaction is believed to proceed through a seven-membered palladacyclic complex in which the regiochemistry of the reaction is controlled by steric factors. A number of 3,4-disubstituted isocoumarins and polysubstituted alpha-pyrones have been prepared in good yields by treating halogen- or triflate-containing aromatic and alpha,beta-unsaturated esters, respectively, with internal alkynes in the presence of a palladium catalyst. Synthetically, the methodology provides an especially simple and convenient regioselective route to isocoumarins and alpha-pyrones containing aryl, silyl, ester, tert-alkyl, and other hindered groups. The reaction is believed to proceed through a seven-membered palladacyclic complex in which the regiochemistry of the reaction is controlled by steric factors.
202 citations
TL;DR: In this paper, 3-substituted isoquinolines and pyridines were synthesized by coupling aryl, alkenyl, and alkyl substituents with the tert-butylimines of o-iodobenzaldehydes or 3-halo-2-alkenals.
149 citations
TL;DR: The palladium-catalyzed annulation of cyclic and bicyclic alkenes, unsaturated cyclopropanes and cyclobutanes, allenes, 1,3- and 1,4-dienes, as well as internal alkynes, by appropriately-substituted aryl or vinylic halides and triflates provides a very efficient, yet versatile route to a wide variety of heterocycles and carbocycles.
147 citations
TL;DR: In this article, the [3 + 4] annulation between vinyldiazoacetates and dienes was used for the stereoselective synthesis of highly functionalized seven-membered rings.
114 citations
TL;DR: The palladium-catalyzed annulation of cyclic and bicyclic alkenes, unsaturated cyclopropanes and cyclobutanes, as well as internal alkynes, by functionally substituted aryl or vinylic halides and triflates provides a very versatile route to a wide variety of heterocycles and carbocycles.
Abstract: The palladium-catalyzed annulation of cyclic and bicyclic alkenes; unsaturated cyclopropanes and cyclobutanes; 1,2-, 1,3- and 1,4-dienes; as well as internal alkynes, by functionally substituted aryl or vinylic halides and triflates provides a very versatile route to a wide variety of heterocycles and carbocycles.
93 citations
TL;DR: In this paper, a one-pot, one-operation procedure consisting of a palladium-catalyzed aryl amination of an ortho-bromobenzaldehyde with a sulfoximine followed by an intramolecular condensation reaction is described.
Abstract: Enantiomerically pure 2,1-benzothiazines are readily prepared by a one-pot, one-operation procedure consisting of a palladium-catalyzed aryl amination of an ortho-bromobenzaldehyde with a sulfoximine followed by an intramolecular condensation reaction [Eq. (1)]. BINAP=1,1′-binaphthalene-2,2′-diylbis(diphenylphosphane).
90 citations
TL;DR: In this article, the synthesis of fused polycyclic quinolines can be viewed as occurring through a tandem concerted Diels-Alder/annulation reactions of β-(2-aminophenyl)-α, β-ynones with enamines, azides and nitrile oxides.
76 citations
TL;DR: In this paper, a variety of indoles, all bearing a methyl group in the 3-position, underwent smooth reaction with 1,1-cyclopropanediesters to yield annulated adducts in fair to excellent yield.
67 citations
TL;DR: Boratabenzenes (4) are six π-electron aromatic anions which can serve as versatile ligands towards Zr(IV) and Zr (II) as discussed by the authors, and on activation by excess methylaluminoxane 11 are catalysts for the polymerization or oligomerization of ethylene.
63 citations
TL;DR: In this article, an interesting annulation reaction of benzynes derived from 2,4-dibromophenol derivatives formed the core of the shortest naphthalene synthesis and an alternative annulation initiated by the addition of a benzylic sulfone anion to methyl crotonate led to an efficient naphthol synthesis amenable to large scale.
Abstract: Efficient syntheses of the title compounds have been developed. Several strategies for preparation of each of the naphthalene and tetrahydroisoquinoline (THIQ) portions were developed. Initial attempts to use benzyne plus furan cycloaddition reactions were thwarted by the unfavorable sense of the regiochemical outcome. An interesting annulation reaction of benzynes derived from 2,4-dibromophenol derivatives formed the core of the shortest naphthalene synthesis. An alternative annulation initiated by the addition of a benzylic sulfone anion to methyl crotonate led to an efficient naphthol synthesis amenable to large scale. The THIQ synthesis of Bringmann was used initially and subsequently complemented by a route whose key step involved the opening of N-tosyl-2-methylethyleneimine by a 3,5-dimethoxyphenylcuprate reagent. The results from a variety of aryl cross-coupling reactions are described. Suzuki coupling of the boronic acid derived from the naphthalene moiety with a THIQ-iodide was the most generally...
TL;DR: In this article, a cyclic sulfate was converted to allylic alcohol via Reich iodoso olefination and E-ring annulation via intermolecular oxygen alkylation of highly functionalized secondary alcohol using rhodium-catalyzed decomposition.
Abstract: Hecogenin acetate (1) was converted to North 1 azidoketone 5 involving several key transformations: (1) conversion of cyclic sulfate 33b to allylic alcohol 40 via Reich iodoso olefination; (2) E-ring annulation via intermolecular oxygen alkylation of highly functionalized secondary alcohol 40 using rhodium-catalyzed decomposition of an α-diazophosphonoacetate to provide α-alkoxyphosphonoacetate 52, with subsequent intramolecular Wadsworth−Emmons reaction to provide alkoxydihydrofuran 53; and (3) establishment of the C20 stereochemistry by chromium(II) reduction of tertiary bromide 86 to a 9:1 mixture of diastereomeric spiroketals 90α/90β, separated as silyl ethers 91α/91β. Conversion of 91α to α-azidoketone 5 was uneventful.
TL;DR: In this article, the cycloaddition reactions of various C-heteroarylimines with α,β-unsaturated Fischer carbene complexes have been studied, depending on the structure of the imine and on the type of unsaturation of the carbene complex.
Abstract: The cycloaddition reactions of various C-heteroarylimines with α,β-unsaturated Fischer carbene complexes have been studied. Either [3 + 3] carbocyclization or [3 + 3] and [4 + 3] heterocyclization reactions were accomplished, depending on the structure of the imine and on the type of unsaturation of the carbene complex. Imines derived from furan-, 4, benzofuran-, 5, and N-methylindole-2-carboxaldehyde, 7, gave C3 + C3 cycloadducts 10−12 on reaction with alkynyl carbene complexes 2a and 3. The reaction of N-unsubstituted pyrrole imine 8a with alkenyl carbene complexes 1 involved the ring nitrogen atom of the pyrrole unit leading to C2N + C3 heterocycloadducts 14 and 15. Moreover, N-unsubstituted imines 8 and 9 underwent C2N2 + C3 heterocyclization to alkynyl carbene complexes 2 and 3 to furnish zwitterionic metalpentacarbonyl containing heterocycles 17 and 18. We have studied the thermal behavior of heterocycles 17, finding that they led to bispyrrole 21 or indolizine 20 when heated at 120 °C in the presen...
TL;DR: In this paper, a methodology has been developed for introduction into the core of C-3 substituents, which are necessary for construction of the "eastern" and "western" macrocyclic rings of 1.
Abstract: Studies have been conducted on testing strategies for annulation of the two macrocyclic rings onto the central tricyclic nucleus of sarain A (1). In particular, methodology has been developed for introduction into the core of C-3‘ and C-3 substituents, which are necessary for construction of the “eastern” and “western” macrocyclic rings of 1, respectively. Formation of the western ring has been successfully addressed via a ring-closing olefin metathesis strategy utilizing the Grubbs ruthenium catalyst. With this macrocyclization approach, a key intermediate lactam has been prepared which will be utilized in a total synthesis of the natural product.
TL;DR: In this article, various spiro cyclic systems are prepared from β-di-carbonyl compounds and active methylene substrates via palladium catalyzed allylation and ring-closing metathesis (RCM) reaction.
Abstract: Various spiro cyclic systems are prepared from β-di-carbonyl compounds and active methylene substrates via palladium catalyzed allylation and ring-closing metathesis (RCM) reaction as key steps.
TL;DR: In this paper, an efficient one-pot annulation reaction between ω-iodo esters and 2-(ω-chloroalkyl)cycloalkanones was proposed.
Abstract: Samarium(II) iodide promotes an efficient one-pot annulation reaction between ω-iodo esters and 2-(ω-chloroalkyl)cycloalkanones. An initial intermolecular carbonyl addition reaction between the iodo ester and the ketone generates a lactone intermediate. The lactone undergoes a subsequent nucleophilic acyl substitution reaction with an organosamarium derived from the chloride. Nickel(II) iodide is an efficient catalyst for the first step of the process, and light is utilized to promote the second step. Seven-, eight-, and nine-membered rings can be accessed by this sequential dianionic process. This annulative approach to carbocycles is complementary to previously reported procedures.
TL;DR: In this paper, various dialkyl and diarylvinylsulfonium salts react with indole-2-carboxaldehydes in the presence of sodium hydride and sodium azide to form tricyclic azido alcohols analogous to 2.
TL;DR: In this paper, aldehydes were added to the new enantiomerically pure lithiated sulfoxide 4 to yield gamma-butenolides of high enantiomersic purities after elimination of phenylsulfinic acid.
TL;DR: This chapter concludes by discussing that many members of the 1,2,4-triazoIo[4,3-c]pyrimidines are shown to possess very interesting biological activities and medicinal applications.
Abstract: Publisher Summary This chapter reviews the chemistry of 1,2,4-triazolopyrimidines. The chapter is devoted to surveying the chemistry of one of the four possible systems of this class of compounds—namely, 1,2,4-triazolo[4,3-a]pyrimidin. The chapter focuses on the chemistry of 1,2,4-triazolo[1,5-c]pyrimidines. This chapter discusses the introduction, synthesis, reactions, spectral properties, and applications of 1,2,4-triazolopyrimidines 11: 1,2,4-triazolo[4,3-c]pyrimidines. It also illustrates that many members of the 1,2,4-triazoIo[4,3-c]pyrimidines are shown to possess very interesting biological activities and medicinal applications. The chapter concludes by discussing that 1,2,4-triazoIo[4,3-c]pyrimidines have been synthesized using several general approaches: (1)annulation of the 1,2,4-triazole ring onto a pyrimidine structure; (2) annulation of the pyrimidine ring onto a 1,2,4-triazole structure; (3) concurrent formation of both of the 1,2,4-triazole and pyrimidine rings; and (4) rearrangement of pyrimido[5,4-e]l,2,4-triazines.
TL;DR: In this article, a convergent approach for the synthesis of indolizidine alkaloids was proposed, which utilizes the available chirality in proline and serine and is conceptually different from other approaches.
Abstract: A general methodology for the synthesis of indolizidine alkaloids δ-coniceine (12), 1-hydroxyindolizidine (20), desacetoxy slaframine (24), slaframine (34), and an analogue (37) has been developed. This convergent approach utilizes the available chirality in proline and serine and is conceptually different from other approaches. A highly stereoselective coupling of the prolinals with a nucleophilic alaninol synthon provides the precursors for the key cyclization. A novel thermolytic annulation of an oxazolidinone is the key step in the formation of the six-membered piperidine ring. Further elaboration provides the target natural products 24, 34, and 37 in good overall yields.
TL;DR: The first total synthesis of the natural enantiomer of the insect-antifeedant dihydroclerodin and lupulin C (40) has been achieved starting from (R)-(−)-carvone (2).
Abstract: The first total synthesis of the natural enantiomer of the insect-antifeedant dihydroclerodin (1) and lupulin C (40) has been achieved starting from (R)-(−)-carvone (2). In the applied strategy, the hexahydrofuro[2,3-b]furan moiety was introduced in an early stage of the synthesis. The correct configuration at C-9, C-11, C-13, and C-16 was established by application of a remarkably diastereoselective Mukaiyama reaction. The desired configuration at C-10 was obtained by catalytic reduction of the intermediate enone 21. After annulation of the second ring, the structural features at C-4, C-5, and C-6 were introduced. The successful finishing of the synthesis included a Chugaev elimination to give the exocyclic double bond at C-4 that is present in lupulin C. Oxidation of this double bond with m-CPBA afforded dihydroclerodin.
TL;DR: In this article, the synthesis of brasiliquinones B and C, 2 and 3 and 3-deoxyrabelomycin 4a has been accomplished in 6-7 steps from the common precursor 18b.
Abstract: Synthesis of brasiliquinones B and C, 2 and 3 and 3-deoxyrabelomycin 4a has been accomplished in 6–7 steps from the common precursor 18b. The key naphthalenones 6 were prepared in 5 steps from tetralone 17 in a regioselective manner. Anionic annulation of cyanophthalide 7c with 6 readily provided tetracyclic precursors 5 in excellent yields, sunlight-promoted photooxidation of which led to the synthesis of the title compounds.
TL;DR: In this paper, the use of uncatalysed displacement reactions of the triflate group represents a very simple method for the synthesis of 4-N-, 4-O-, and 4-S-substituted thiazoles.
TL;DR: In this article, double Michael reactions with equatorially disposed cyano groups are used to obtain cyclic ketones with pendant ketone, nitrile, and ester functionality.
Abstract: Two carbon acids connected by a tether containing a ketone undergo two Michael reactions to 3-butyn-2-one to afford highly substituted and functionalized cyclic ketones with pendant ketone, nitrile, and ester functionality. The stereochemical courses of the double Michael reactions vary remarkably with the structure of the starting material. Double Michael adducts with equatorially disposed cyano groups can be hydrogenated to afford trans-fused bicyclic amines.
TL;DR: In this paper, 5-Iodopentofuranosides are converted with zinc and allyl/propargyl bromide into dienes/enynes which are further used in carbohydrate annulation reactions.
TL;DR: The carbonate groups, rarely seen in ruthenium carbonyl complexes, are responsible for the observed annulation, and hold consecutive Ru dimers together by acting as bridging and doubly chelating ligands.
Abstract: We just need to mix [Ru(CO)(3)Cl(2)(thf)] with methanolic NEt(4)OH-nature will do the rest: The unsaturated fragments thus generated spontaneously polymerize with production of CO(2) and H(2)O, which combine to give the carbonate ligands of the ruthena-crown species obtained (shown schematically). The carbonate groups, rarely seen in ruthenium carbonyl complexes, are responsible for the observed annulation, and hold consecutive Ru dimers together by acting as bridging and doubly chelating ligands.
TL;DR: A new formal stereoselective synthesis of (+)-huperzine A 1 was achieved using as a key step a palladium mediated annulation between 2-methylene-1,3-propanediol diacetate and (1R,2S)-2-phenylcyclohexanol derived β-ketoester 14.
TL;DR: In this article, a prepackaged method for modified Khand cycloadditions is described; vinyl esters are employed as the olefinic reaction partner to provide cyclopentenone products more normally obtained with ethylene.