Showing papers on "Annulation published in 1992"
TL;DR: The (S)-tryptophan derived catalyst has been used to effect enantioselective Mukaiyama-aldol and aldol-dihydropyrone annulation reactions of trimethylsilyloxy olefins and dienes.
183 citations
TL;DR: Allyl and propargyl-silanes can serve as three-carbon components in a [3+2] annulation strategy for the synthesis of five-membered carbocycles and heterocycles as discussed by the authors.
Abstract: Allyl- and propargylsilanes can serve as three-carbon components in a [3+2] annulation strategy for the synthesis of five-membered carbocycles and heterocycles
113 citations
TL;DR: A new imide chiral auxiliary, endo-7-(2-benzoxazolyl)-1,5,7-trimethyl-3-azabicyclo[3.3.1]nonan-2-one (5), is from Kemp's triacid and resolved via its menthyl carbamate.
Abstract: A new imide chiral auxiliary, endo-7-(2-benzoxazolyl)-1,5,7-trimethyl-3-azabicyclo[3.3.1]nonan-2-one (5), is from Kemp's triacid and resolved via its menthyl carbamate. Mixed fumarate derivatives of the auxiliary show unprecedented control of regiochemistry and β-stereochemistry in representative radical addition reactions. Chiral radicals derived from 5 also show extremely high levels of stereoselectivity in representative radical allylation and cyclization reactions. Structural features of the chiral auxiliary and features of radical addition are integrated into a model for stereoselection
99 citations
TL;DR: In this article, a general method for the synthesis of γ-and δ-lactones through the intramolecular addition of alkoxycarbonyl radicals, formed by reaction of Se-phenylselenocarbonates with n-Bu 3 SnH, onto carbon-carbon multiple bonds is described.
Abstract: A general method for the synthesis of γ-and δ-lactones through the intramolecular addition of alkoxycarbonyl radicals, formed by reaction of Se-phenylselenocarbonates with n-Bu 3 SnH, onto carbon-carbon multiple bonds is described. This free-radical cyclization is characterized by high regioselectivity favoring exo addition and by a high ratio of cyclization to reduction.Monocyclic,fused bicyclic, and spirocyclic lactones are formed in good to excellent yield.Use of allyltri-n-butyltin as a chain-transfer agent in the place of n-Bu 3 SnH affords the corresponding 3-butenyl lactones
87 citations
TL;DR: In this paper, a method for the synthesis of benzofurans from o-iodophenol and acetylenic compounds under palladium-catalysed conditions is described, which is a convenient and general method for benzofuran synthesis.
Abstract: A convenient and general method for the synthesis of benzofurans from o-iodophenol and acetylenic compounds under palladium-catalysed conditions is described.
66 citations
TL;DR: The first total synthesis of (+)-tetronomycin (1), a novel tetronic acid ionophore antibiotic, has been achieved through the synthesis and assemblage of the four cyclic segments 4, 5, 7, and 8 as mentioned in this paper.
Abstract: The first total synthesis of (+)-tetronomycin (1), a novel tetronic acid ionophore antibiotic, has been achieved through the synthesis and assemblage of the four cyclic segments 4, 5, 7, and 8 Construction of the C 5 -C 13 cyclohexyl portion 5 involves as the key step either a Beckmann fragmentation of the bicyclic ketone oxime 45 or an L-Selectride-mediated reductive annulation of the nona-2,7-dienoate 53 The C 1 4-C 2 8 polyether fragment 6 was constructed by a BF 3 -catalyzed coupling reaction of the C 1 4-C 2 2 allylsilane 7 and the C 2 3-C 2 8 tetrahydrofuran 8 which were derived, respectively, from L-ascorbic acid or (R)-3-hydroxyisobutyrate and L-rhamnal
64 citations
TL;DR: Aromatic imines react with phenylacetylene or styrene in an acetonitrile solution of iron(III) chloride to give quinolines 3 or their tetrahydro derivatives 11 together with variable amounts of products arising from the reduction of the imines.
Abstract: Aromatic imines react with phenylacetylene or styrene in an acetonitrile solution of iron(III) chloride to give quinolines 3 or their tetrahydro derivatives 11 together with variable amounts of products 4 arising from the reduction of the imines. The initial atep appears to be a one-electron oxidation to generate iron(II) and an imine radical cation. When the reactions are carried out in the presence of stoichiometric amounts of tetrachloro-p-benzoquinone (chloranil), only quinolines 3 are obtained
55 citations
TL;DR: In this paper, a highly stereoselective 3 + 2 annulation has been developed by cyclopropanation of vinyl ethers with rhodium(II)-stabilized vinylcarbenoids to generate vinylcyclopropanes followed by a Et 2 AlCl-catalyzed 1,3-sigmatropic rearrangement.
Abstract: A highly stereoselective 3 + 2 annulation has been developed by cyclopropanation of vinyl ethers with rhodium(II)-stabilized vinylcarbenoids to generate vinylcyclopropanes followed by a Et 2 AlCl-catalyzed 1,3-sigmatropic rearrangement. The success of this methodolgy rests on the remarkably stereoselectivity that is exhibited in both the cyclopropanation step and also the Et 2 AlCl-catalyzed vinylcyclopropane rearrangement
53 citations
TL;DR: In this article, the palladium-catalyzed cycloaddition of trimethylenemethane to an activated octalone with complete control of π-facial selectivity is described.
Abstract: The total synthesis of three hydroxykempenones has been accomplished. The retrosynthetic elements of the strategy focused on setting four key stereocenters in rings A and B, followed by annulation of ring C and ultimate cyclization to construct the seven-membered ring, D. Since the target molecule carries eight contiguous stereogenic centers, proper attention to stereocontrolled processes was mandatory. The key features of the scheme include the palladium-catalyzed[3+2] cycloaddition of trimethylenemethane to an activated octalone with the complete control of π-facial selectivity, fully regiospecific monooxidation of a diol with ammonium molybdate uniquely at the secondary site to provide a key hydroxy ketone, hydroxyl-directed hydride reduction of the latter intermediate in order to override a contrary kinetic preference for nucleophilic attack, avoidance of Grob fragmentation in diaxial, monofunctionalized 1,3-diols, and selective deoxygenation of a diol
51 citations
TL;DR: The Wieland-Miescher ketone lends itself to conversion, in a few steps, to intermediates which could well be useful for a synthesis of taxol and analogs thereof.
Abstract: The Wieland-Miescher ketone lends itself to conversion, in a few steps, to intermediates which could well be useful for a synthesis of taxol (1) and analogs thereof
44 citations
TL;DR: In this article, the aza-annulation of imines with activated acrylate derivatives was studied as a means of preparing the corresponding 1,2,3,4-tetrahydro-2-pyridones.
Abstract: The aza-annulation of imines with activated acrylate derivatives was studied as a means of preparing the corresponding 1,2,3,4-tetrahydro-2-pyridones. Through the use of reagents known to facilitate the formation of amide bonds from carboxylic acids, several methods of activatin the acrylate species were compared. The acrylate derivatives studied were acryloyl chloride and acrylic anhydride as well as acrylic acid activated by reaction with EtO 2 CCl, (PhO) 2 P(O)N 3 , or MCPI
TL;DR: Heating of allyl iodomalononitriles with alkenes, followed by tin hydride reduction, forms 1-(cyanalkyl)-4-cyanocyclopentane rings with up to 5 new stereocenters by a sequence of atom transfer addition followed by nitrile transfer cyclization.
TL;DR: A photochemical aromatic annulation strategy provides efficient synthetic routes to the diterpenoid quinones (+)-danshexinkun A, danshex-inkun B, Danshexin-C, (−)-dihydrotanshinone I, and tansinone I.
Abstract: The chromium(0)-carbene complex benzannulation reaction was shown to be applicable to cyclodec-4-yn-1-one. Significant regioselectivity was realized in this reaction with ortho-substituted benzylchromium complexes. Reactions of a novel resultant fused cyclodecenone-naphthoquinone with several bases have been studied. Products apparently arising from either intramolecular Michael addition of a ketone enolate to the quinone or intramolecular aldol condensation of a quinone-stabilized anion with the ketone have been observed. The latter mode constitutes a route to the title substructure and, in principle, a route to reach certain angucycline antibiotics
TL;DR: In this paper, a new annulation method involving a boron trifluoride catalysed addition of trialkylsilyl enol ethers to methyl vinyl ketone (MVK) in the presence of a hydroxylic compound was presented.
Abstract: A new annulation method is presented, involving a boron trifluoride catalysed Michael addition of trialkylsilyl enol ethers to methyl vinyl ketone (MVK) in the presence of a hydroxylic compound. This methodology allows regiospecific 3-oxobutylation of either of the two isomeric enol ethers of mono or di-substituted cyclanones. Octalones 2d, e and hydrindenones 17 with the two alkyl groups in a cis relationship can thus be specifically obtained. This method has been applied to a short and efficient preparation of (±)-dehydrofukinone 10.
TL;DR: Aza-Wittig reaction of bis(iminophosphorane) 4 with 2 equiv of isocyanate leads directly to pyrido[2,3,4-de]quinazolines 5 as mentioned in this paper.
Abstract: Aza-Wittig reaction of bis(iminophosphorane) 4 with 2 equiv of isocyanate leads directly to pyrido[2,3,4-de]quinazolines 5. Iminophosphoranes 8, available from 4 and 1 equiv of the appropriate isocyanate, react either with 1 equiv of isocyanate or ketene to give pyrido[2,3,4-de]quinazolines 9 or benzo[de][1,6]naphthyridines 10, respectively. Bis(iminophosphorane) 4 by sequential treatment with aldehydes and isocyanates yielded 2,3-dihydropyrido[2,3,4-de]quinazolines 17
TL;DR: The allylstannane 1 and the vinylstannanes 3, 5 and 7 cyclise when treated with butyl-lithium as discussed by the authors, which is the only known butyl acidity property.
TL;DR: In this article, propargyl iodomalonitrile with mono-, di- or trisubstituted alkenes followed by reduction of the crude or isolated products with tributyltin hydride produces dicyano(methylene)cyclopentanes in good to excellent overall yield.
TL;DR: Pd-catalyzed reaction of 3-acetoxy-8-butenyl- ( 9 ) and 8-but-3-inyl-bicyclo[3.3.0]oct-1-ene ( 11 ) with CO in CH3COOH lead via double annulation to all-cis[5.5]fenestranes as mentioned in this paper
TL;DR: In this paper, the key intermediate in the proposed synthesis of the guaianolide sesquiterpene geigerin was prepared by a novel sequence of reactions which includes a chemoselective oxy-Cope transformation of enynols of general structure.
Abstract: Furano alcohol 5, the key intermediate in our proposed synthesis of the guaianolide sesquiterpene geigerin (1), was prepared by a novel sequence of reactions which includes a chemoselective oxy-Cope transformation of enynols of general structure 42. Although 42 itself underwent oxy-Cope reaction with exclusive triple-bond participation, the corresponding tert-butyldimethylsilyl ether 46 gave the desired vinyl silyloxy Cope product 48 with 100% selectivity. The conversion of acetylenic oxazole 48 to 5 was then effected by a highly efficient (Diels-Alder)-(retro-Diels-Alder) transformation to generate the guaiane ketone 20, followed by hydride reduction
TL;DR: In this paper, a facile new one pot annulation of monobromoquinones 7 to the vinylogous carbamate 3 provides a direct route to the pyrroloindoloquinone framework.
TL;DR: The ISMS reaction, which initially afforded a mixture of regioisomeric olefins, can now be controlled to produce only the exocyclic alkene.
TL;DR: Optically pure β-aminopiperidines can be prepared in high yields though a thermolytic annulation sequence involving ring opening of an oxazolidinone.
Abstract: Optically pure β-aminopiperidines can be prepared in high yields though a thermolytic annulation sequence involving ring opening of an oxazolidinone
TL;DR: Dimethyl 9,10-dihydro-9, 10-dioxobenzo[f]quinoline-2,4-dicarboxylate (4) was synthesized, and its physical and chemical properties were compared to those of the trimethyl ester of PQQ (PQQTME,2 and the 1-methyl derivative (3) as mentioned in this paper.
Abstract: Dimethyl 9,10-dihydro-9,10-dioxobenzo[f]quinoline-2,4-dicarboxylate (4) was synthesized, and its physical and chemical properties were compared to those of the trimethyl ester of PQQ (PQQTME,2 and the 1-methyl derivative (3). The synthesis of 4 was accomplished by a Doebner-von Miller-type annulation between 3-amino-2-naphthol and dimethyl 2-oxoglutaconate and a subsequent oxidation with Fremy's salt. The electronic effect of the pyrrole nucleus of coenzyme PQQ (1) was examined by comparing the reactivity of 4 to that of 2 and 3 in the acetone adduct formation reaction, the redox reaction with phenylhydrazine, and the aerobic autorecycling oxidation of benzylamine
TL;DR: In this article, a highly stereocontrolled synthesis of (±)-paulownin (1a) and isogmelinol (1b) is reported involving intramolecular radical cyclisation reaction as a key step.
TL;DR: In this article, intramolecular benzannulation reactions of siloxycarbene compounds of manganese bearing tethered alkynes produce functionalized naphtoquinones in efficient fashion with complete regioselectivity under photochemical conditions.
Abstract: Here we report that intramolecular benzannulation reactions of siloxycarbene compounds of manganese bearing tethered alkynes produce functionalized naphtoquinones in efficient fashion with complete regioselectivity under photochemical conditions.
TL;DR: In this article, a sealed tube in the presence of a hydrogen atom source yields naphthalene derivatives 3a, 3b, and 4 in yields of 53-72%.
TL;DR: Rhodium(II) carboxylate stabilized vinylcarbenoids reacted intermolecularly with benzenoid compounds by two distinct modes: cyclopropanation and Cope rearrangement as discussed by the authors.
Abstract: Rhodium(II) carboxylate stabilized vinylcarbenoids reacted intermolecularly with benzenoid compounds by two distinct modes. With benzene, alkylbenzenes, and 1-methoxynaphthalene, 3+4 annulations were observed, presumably arising through initial cyclopropanation followed by a Cope rearrangement. In contrast, alkylation products were formed with methoxy-substituted benzenes. In an intramolecular reaction a delicate balance existed between norcaradiene formation, 3+4 annulation, and 3+2 annulation