Showing papers on "Annulation published in 2002"
TL;DR: The total synthesis of the isoquinoline natural product decumbenine B has been accomplished in seven steps and 20% overall yield by employing this palladium-catalyzed coupling and cyclization methodology.
Abstract: Monosubstituted isoquinolines and pyridines have been prepared in good to excellent yields via coupling of terminal acetylenes with the tert-butylimines of o-iodobenzaldehydes and 3-halo-2-alkenals in the presence of a palladium catalyst and subsequent copper-catalyzed cyclization of the intermediate iminoalkynes. In addition, isoquinoline heterocycles have been prepared in excellent yields via copper-catalyzed cyclization of iminoalkynes. The choice of cyclization conditions is dependent upon the nature of the terminal acetylene that is employed, as only aryl and alkenyl acetylenes cyclize under the palladium-catalyzed reaction conditions that have been developed. However, aryl-, vinylic-, and alkyl-substituted acetylenes undergo palladium-catalyzed coupling and subsequent copper-catalyzed cyclization in excellent yields. The total synthesis of the isoquinoline natural product decumbenine B has been accomplished in seven steps and 20% overall yield by employing this palladium-catalyzed coupling and cyclization methodology.
198 citations
TL;DR: The core of teleocidin B4, a complex fragment of a natural product containing two quaternary stereocenters and a penta-substituted benzene ring, was synthesized in four C-C bond-forming steps starting from tert-butyl derivative 1.
Abstract: The core of teleocidin B4, a complex fragment of a natural product containing two quaternary stereocenters and a penta-substituted benzene ring, was synthesized in four C-C bond-forming steps starting from tert-butyl derivative 1. The first step involved alkenylation of the tert-butyl group with a vinyl boronic acid, followed by the successful annulation of the cyclohexane ring to the benzene nucleus via an intramolecular Friedel-Crafts reaction. The third step required a diastereoselective oxidative carbonylation of the geminal dimethyl group, followed at last by indole assembly via the alkenylation of the phenol nucleus, to afford the teleocidin B4 core. Noteworthy is the fact that steps 1 and 3 critically depended on the directing role of the aniline nitrogen (directed C-H bond functionalization).
161 citations
TL;DR: This reaction represents one of the first examples of the addition of an organopalladium moiety to the carbon-nitrogen triple bond of a nitrile and is compatible with a number of functional groups.
Abstract: 2-Iodobenzonitrile, its derivatives, and various heterocyclic analogues undergo palladium(0)-catalyzed annulation onto diarylacetylenes or bicyclic alkenes to afford 2,3-diarylindenones and polycyclic aromatic ketones in very good to excellent yields. This reaction represents one of the first examples of the addition of an organopalladium moiety to the carbon−nitrogen triple bond of a nitrile. The reaction is compatible with a number of functional groups. A reaction mechanism, as well as a model accounting for the electronic effects of substituents on the aromatic ring of the nitrile, is proposed.
155 citations
TL;DR: An efficient synthesis of the antitumor alkaloid (+/-)-strychnofoline is documented and the ability to conduct annulation reactions of spirocyclopropyloxindoles with functionalized cyclic imines provides new avenues for the preparation of this important class of biologically active structures.
Abstract: An efficient synthesis of the antitumor alkaloid (±)-strychnofoline is documented. Key to the development of the highly convergent strategy delineated is the coupling of a cyclic imine with spiro[cyclopropan-1,3‘-oxindole], which takes place in a highly diastereoselective manner. The ability to conduct annulation reactions of spirocyclopropyloxindoles with functionalized cyclic imines provides new avenues for the preparation of this important class of biologically active structures.
135 citations
TL;DR: In this article, an Oxime-derived, chloro-bridged palladacycles 16 are used for the Heck vinylation of aryl halides, which can be performed under aerobic conditions, with aryls iodides, bromides and chlorides with acrylic esters and olefins displaying turnover numbers (TON) of up to 1010 for phenyl iodide and turnover frequencies (TOF) of 1.4×108 h−1.
Abstract: Oxime-derived, chloro-bridged palladacycles 16 are efficient complexes for the Heck vinylation of aryl halides. The isolated catalysts are thermally stable, not sensitive to air or moisture and easily accessible from inexpensive starting materials. The reaction can be performed under aerobic conditions, with aryl iodides, bromides and chlorides with acrylic esters and olefins displaying turnover numbers (TON) of up to 1010 for phenyl iodide and turnover frequencies (TOF) of 1.4×108 h−1. Deactivated aryl bromides undergo the Heck reaction with styrene with TON and TOF values up to 97,000 and 6063 h−1, respectively. Even aryl chlorides undergo the coupling reaction with olefins with TON up to 920. Complexes 16 catalyze the synthesis of 2,3-disubstituted indenones and indoles in good yields via annulation reaction of internal alkynes with o-bromo- or o-chlorobenzaldehyde and o-iodoaniline, respectively.
129 citations
TL;DR: A synthetic application is illustrated to stereoselectively transform the resulting dihydropyridines to cis-1-azadecalins with unique anti relative stereochemistry at C2 and C2a, leading to synthesis of epi isomers of (-)-pumiliotoxin C.
Abstract: Evidence is described here to support that a highly stereoselective 6π-electron electrocyclic ring closure of 1-azatrienes is a key step in formal [3 + 3] cycloaddition or annulation reactions of chiral vinylogous amides with α,β-unsaturated iminium salts. This would represent the first highly stereoselective 6π-electron electrocyclic ring closure of 1-azatrienes. We have also unambiguously demonstrated that these specific ring closures are reversible, leading to the major diastereomer that is also thermodynamically more stable, and that a rotation preference likely also plays a role. A synthetic application is illustrated here to stereoselectively transform the resulting dihydropyridines to cis-1-azadecalins with unique anti relative stereochemistry at C2 and C2a, leading to synthesis of epi isomers of (−)-pumiliotoxin C.
100 citations
TL;DR: In this paper, the synthesis of fused polycyclic ethers from the coupling of C-glycoside forming reactions with ring closing metathesis and acid mediated annulation reactions is described.
87 citations
TL;DR: A general synthetic methodology for palladium-catalyzed carbonylative annulation of o-alkynylphenol to construct 2-substituted-3-aroyl-benzo[b]furan is reported and could be applied to a wider selection of iodide substrates to generate desired products.
Abstract: We report here a general synthetic methodology for palladium-catalyzed carbonylative annulation of o-alkynylphenol to construct 2-substituted-3-aroyl-benzo[b]furan. On the basis of the results, this methodology could be applied to a wider selection of iodide substrates to generate desired products. In accordance with mechanistic studies, this process involves coordination of cationic and less hindered acyl palladium complexes with o-alkynylphenols to create a desired cascade triad (coordination, nucleophilic addition, and reductive elimination). Consistent with this mechanism, addition of 1 equiv of AgBF4 to palladium catalyst Pd(Ph3P)4 generates an ideal candidate for this unique transformation.
80 citations
TL;DR: In the presence of indium triflate or gallium chloride, a novel coupling between internal alkynes and aldehydes occurred to give unsaturated ketones and [4+1] annulation products as mentioned in this paper.
79 citations
78 citations
TL;DR: In this article, a highly efficient method for cyclopentene annulation onto α,β-unsaturated ketones is described, where Indium-mediated 1,4-propargylation onto α-β-un saturated ketones in the presence of tert-butyldimethylsilyl triflate and dimethyl sulfide gives the 6-siloxy-5-en-1-yne derivatives, which undergo W(CO)5(L)-catalyzed 5-endo-dig cyclization to give the corresponding cyclopENTene derivatives
TL;DR: Indoles are produced regioselectively and in moderate yields by two new processes in a two-step sequence involving the (uncatalyzed) reaction of ArNO with alkynes, followed by reduction of the intermediate adduct.
TL;DR: This sequences allows for the asymmetric convergent union of two aldehydes with silyl-stannane reagent 1 in a two-step process: catalytic asymmetric allylation of the first aldehyde using 1 with a BITIP catalyst, followed by reaction of the alcohol so obtained with a second alde Hyde and TMSOTf.
TL;DR: These procedures constitute efficient methods for rapid carbocyclization and annulation of carbohydrates to produce a variety of functionalized five- and six-membered ring systems.
Abstract: Methyl 5-deoxy-5-iodo-pentofuranosides are reductively ring-opened and propargylated in a tandem fashion in the presence of zinc. The 1,7-enynes thus obtained are subjected to ring-closing enyne metathesis with catalyst B to produce functionalized 1-vinyl cyclohexenes. By adding BnNH2 to the tandem reaction, an amino group can be introduced in the 1,7-enyne products. Addition of 2-TMS-ethynylcerium(III) chloride after the reductive ring-opening produces the corresponding 1,6-enynes. Further annulation of the product 1,3-dienes can be achieved through a Diels−Alder reaction with good control of stereochemistry. These procedures constitute efficient methods for rapid carbocyclization and annulation of carbohydrates to produce a variety of functionalized five- and six-membered ring systems.
TL;DR: Indoles are produced regioselectively and in moderate yields from the reactions of nitroaromatics with alkynes catalyzed by [CpM(CO)2]2 (1; [(η5-C5H5)Fe(CO), 2]2] under carbon monoxide as discussed by the authors.
TL;DR: The annulation reaction provided a new entry to thiazolines, particularly those with 2-aryl substituents, particularlythose with 2,3-dienoates.
Abstract: The annulation of thioamides with 2-alkynoates and 2,3-dienoates under the catalysis of tri-n-butylphosphine was described. The annulation reaction provided a new entry to thiazolines, particularly those with 2-aryl substituents.
TL;DR: A convergent synthesis of a pyrimidine core has been achieved by treating alpha, alpha-dibromo oxime ethers with a variety of Grignard reagents in good yields as mentioned in this paper.
Abstract: A convergent synthesis of a pyrimidine core has been achieved Treatment of alpha,alpha-dibromo oxime ethers, which are easily derived from the corresponding esters, with a variety of Grignard reagents provides trisubstituted pyrimidines in good yields This new method offers an easy access to functionalized pyrimidines
TL;DR: Silica chloride (SiO(2)Cl)/DMSO, as a heterogeneous system, has been efficiently used for deprotection of thioacetals into aldehydes in dry CH(2,4-dithiins) at room temperature in good yields.
Abstract: Silica chloride (SiO2Cl)/DMSO, as a heterogeneous system, has been efficiently used for deprotection of thioacetals into aldehydes in dry CH2Cl2 at room temperature. Thioketals without enolizable hydrogens adjacent to a sulfur atom are converted easily to the corresponding ketones in high yields under similar reaction conditions. However, thioketals with enolizable methyl and methylene groups undergo ring-expansion reactions to afford 1,4-dithiepins and 1,4-dithiins in dry CH2Cl2 at room temperature in good yields.
TL;DR: The Sonogashira-Heck-Cassar reaction was shown to be a facile and convenient route for the synthesis of 1-ferrocenyl-2-hetero-acetylenes in high yields as mentioned in this paper.
TL;DR: Palladium-catalyzed stereoselective annulation of a functional vinylstannane by acyl chlorides gives the corresponding α-pyran-2-ones in good yields.
Abstract: Palladium-catalyzed stereoselective annulation of a functional vinylstannane by acyl chlorides gives the corresponding α-pyran-2-ones in good yields. This annulation most probably proceeds through a Stille reaction/cyclization sequence.
TL;DR: The synthesis of (+/-)-peduncularine was accomplished using the [3 + 2] annulation of an allylic silane with chlorosulfonyl isocyanate to assemble the bicyclic core of the alkaloid.
Abstract: The synthesis of (±)-peduncularine was accomplished using the [3 + 2] annulation of an allylic silane with chlorosulfonyl isocyanate to assemble the bicyclic core of the alkaloid. The stereochemistry of the annulation product was employed to control the installation of the indolylmethyl side chain at C-7 with complete stereoselectivity.
TL;DR: In this article, the palladium-catalyzed annulation of internal and terminal acetylenes has been used for the synthesis of a wide range of alkynes, including aryl-, alkyl-, hydroxymethyl-, ethoxycarbonyl-, and trimethylsilyl-substituted alkynes.
Abstract: A variety of substituted beta- and gamma-carbolines have been prepared in moderate to excellent yields by the palladium-catalyzed annulation of internal and terminal acetylenes by the tert-butylimines of N-substituted 3-iodoindole-2-carboxaldehydes and 2-haloindole-3-carboxaldehydes, respectively. This annulation chemistry is effective for a wide range of alkynes, including aryl-, alkyl-, hydroxymethyl-, ethoxycarbonyl-, and trimethylsilyl-substituted alkynes. When an unsymmetrical internal alkyne is employed, this method generally gives two regioisomers. When a terminal alkyne is employed, only one regioisomer has been isolated. This palladium-catalyzed annulation chemistry has also been successfully applied to the synthesis of two biologically interesting beta-carboline alkaloids, ZK93423 and abecarnil (ZK112119).
TL;DR: The general utility of this methodology is illustrated by an intramolecular annulation between sp and sp 3 centers as mentioned in this paper, which can be used to obtain an Ag 2 O/CrCl 2 mediated homocoupling in moderate to good yields under mild conditions.
TL;DR: A palladium(II)-mediated cascade carbonylative annulation of o-alkynylphenols was achieved successfully on silyl linker-based macrobeads, which led to an efficient combinatorial synthesis of a 2,3-disubstituted benzo[b]furan library.
TL;DR: In the presence of a rhodium catalyst, 4-alkynals react with alkynes to furnish cyclohexenones via metalacycle 1; as far as we are aware, this is the first example of the generation of this class of compounds through such a transformation as mentioned in this paper.
TL;DR: This palladium-catalyzed carboannulation of internal alkynes forms two new carbon-carbon bonds in a single step, accommodates a variety of functional groups, and affords excellent yields of highly substituted naphthalenes.
TL;DR: The [3 + 2] annulation reaction of allylsilane 1 with an alpha-keto ester provided the highly substituted tetrahydrofuran 2 as a single diastereomer in high yield and the synthesis of (+/-)-5-epi-citreoviral and (-/-)-citreviral has been accomplished with this annulation Reaction as the key step.
TL;DR: A novel method for the synthesis of phthalides and 3,4-dihydroisocoumarins via the palladium-catalyzed intramolecular benzannulation of bis-enyne and enyne-diyne systems is described.
Abstract: A novel method for the synthesis of phthalides and 3,4-dihydroisocoumarins via the palladium-catalyzed intramolecular benzannulation of bis-enyne and enyne-diyne systems is described. Various kinds of substituted phthalides 9 and 17 and 3,4-dihydroisocoumarins 19 were synthesized from 8, 16, and 18, respectively, in moderate to excellent yields. The benzannulation reaction proceeded chemoselectively to give the corresponding fused ring compounds A without the formation of the regioisomeric products B (eq 6). Furthermore, this methodology was applied to the synthesis of biologically active 3-n-butylphthalide 23.
TL;DR: In this paper, a new aromatic annulation reaction based on sequential Horner-Emmons and Claisen condensation reactions is described, which provides a rapid entry to arylnaphthalenes.