Showing papers on "Annulation published in 2009"
TL;DR: A palladium-catalyzed domino aminopalladation/C-H functionalization sequence has been developed, and provides access to functionalized phenanthridines and isoquinolines.
Abstract: A palladium-catalyzed domino aminopalladation/C-H functionalization sequence has been developed, and provides access to functionalized phenanthridines and isoquinolines. The use of butyronitrile as the solvent is determinant to the success of the domino process. [on SciFinder (R)]
266 citations
TL;DR: The results clearly demonstrate that the dichotomous catalytic behavior of the iron catalyst, which is transition-metal catalyst in the oxidative coupling step and Lewis acid in the condensation step, is the same as that of the conventional catalyst.
Abstract: The combination of FeCl(3) x 6 H(2)O and di-tert-butyl peroxide offers a novel and efficient method for the construction of polysubstituted benzofurans 3 from the reaction of simple phenols 1 and beta-keto esters 2, which are expected to give coumarins in the well-known Pechmann condensation. A variety of phenols reacted with beta-keto esters to provide a range of benzofuran products in moderate to excellent yields. The regio-specific annulation was proven by the X-ray molecular structure of the product 3k. Hydrate of FeCl(3) is essential for an achievement of the present transformation. The kinetic isotopic effect (KIE) experiments were carried out by competition experiments and displayed a k(H)/k(D) = 1.0 +/- 0.1. The kinetic isotopic effect indicated that aromatic C-H bond cleavage is not involved in the rate-determining steps of the present transformation. Moreover, the results clearly demonstrate that the dichotomous catalytic behavior of the iron catalyst, which is transition-metal catalyst in the oxidative coupling step and Lewis acid in the condensation step. The possible intermediate 5 was synthesized and converted into the desired benzofuran 3a under the reaction conditions. A tentative mechanism of the formation of benzofurans 3 was proposed.
221 citations
TL;DR: The gold-catalyzed [3+3]-cycloaddition reaction of propargyl esters and azomethine imines has been developed and a stepwise mechanism involving addition of the 1,3-dipole to a gold-carbenoid intermediate is proposed.
Abstract: The gold-catalyzed [3+3]-cycloaddition reaction of propargyl esters and azomethine imines has been developed. The reaction provides a rapid entry into a wide range of substituted tetrahydropyridazine derivatives from simple starting materials. A stepwise mechanism involving addition of the 1,3-dipole to a gold-carbenoid intermediate is proposed.
191 citations
TL;DR: Palladium complexes of 1,3,5,7-tetramethyl-2,4,8-trioxa- 6-phenyl-6-phosphaadamantane are shown to be effective catalytic systems facilitating the sequential application of a microwave-assisted Sonogashira and carbonylative annulation reaction for the preparation of substituted flavones.
138 citations
TL;DR: It is reported that alpha'-hydroxyenones, which can be prepared in a single convenient step from aromatic and heteroaromatic aldehydes, can serve as efficient surrogates for enals in the annulation reactions.
Abstract: N-heterocyclic carbene-catalyzed reactions of α,β-unsaturated aldehydes and a variety of electrophiles allow the facile preparation of a diverse array of annulation products including trisubstituted cyclopentenes, γ-lactams, and bicyclic β-lactams. The substrate scope of these reactions, however, is limited by the difficulties of preparing the starting α,β-unsaturated aldehydes. We now report that α′-hydroxyenones, which can be prepared in a single convenient step from aromatic and heteroaromatic aldehydes, can serve as efficient surrogates for enals in the annulation reactions. This protocol allows the facile preparation and use of substrates bearing nitrogen heterocycles. These reagents have also allowed us to demonstrate that, in contrast to other classes of aldehydes, the formation of the Breslow intermediate from enals and N-heterocyclic carbenes is irreversible under the reaction conditions.
137 citations
TL;DR: These studies provide both an efficient entry to valuable chiral structures and a dramatic demonstration of stereodivergency of chiral imidazolium versus triazolum-derived N-heterocyclic carbene catalysts.
115 citations
TL;DR: A phosphine-catalyzed [4 + 3] annulation of modified allylic carbonates with methyl coumalate was developed and offered a powerful method for the construction of bicyclo[3.2.2]nonadiene skeleton with high stereoselectivity.
113 citations
TL;DR: A Pd-catalyzed Larock annulation provides expedient access to a subset of resveratrol-derived natural products and resulted in the structural revision of an intermediate en route to the natural product pauciflorol F.
110 citations
TL;DR: The method accommodates a range of nitrogen substituents and the amino alcohol can be substituted by amino thiols and diamines to give thiomorpholines, piperazines and benzodiazepines.
106 citations
TL;DR: A phosphane-catalyzed [3 +2] annulation of g-methyl allenoates with aromatic aldehydes provides a convergent and efficient synthesis of 2-alkylidenetetrahydrofurans, which are versatile synthetic building blocks for a vast array of 5-membered oxygenated heterocycle derivatives.
Abstract: Five-membered oxygen-containing heterocycles are important structural components in a diverse range of naturally occurring and pharmacologically active molecules. Their widespread occurrence in the structures of natural or artificial bioactive substances has stimulated considerable interest in the development of new, efficient preparation methods. Among numerous known synthetic methods, the convergent annulation, which features both C O and C C bond formation in one step, is one of the promising strategies to construct oxygen-containing heterocycles from simple and stable starting materials. Previously, only a few such examples were reported. Herein, we report a phosphane-catalyzed [3 +2] annulation of g-methyl allenoates with aromatic aldehydes. This annulation provides a convergent and efficient synthesis of 2-alkylidenetetrahydrofurans, which are versatile synthetic building blocks for a vast array of 5-membered oxygenated heterocycle derivatives. Recently, phosphane-catalyzed cycloaddition reactions of allenes have been widely applied in the construction of a variety of carboand heterocycles. Among them, [3+2] and [4+ 2] cycloadditions of allenoates with electron-deficient olefins or imines are especially attractive because they provide metal-free and highly atom economic strategies to build fiveand six-membered ring systems. However, aldehydes as electrophiles in reactions with allenoates show distinctive reactivity patterns relative to electron-deficient olefins and imines. As a result, the corresponding [3+2] and [4+ 2] annulations of allenoates with aldehydes have not been developed to the same extent as annulations with activated olefins or imines. On the basis of experimental and theoretical studies by Kwon and co-workers, the difference in the reactivity patterns of allenoates with aldehydes, olefins, and imines has been well rationalized. 9] Under the nucleophilic catalysis of a phosphane, activated olefins and imines undergo predominant a addition to the nonsubstituted allenoate (R’= H), leading to [3+ 2] cycloaddition products (Scheme 1, pathway A). In sharp contrast, aldehydes undergo exclusive g addition to the allenoate, resulting in the formation of a cyclic adduct, for example, 1,3-dioxan-4-ylidene, rather than the normal [3+2] cycloaddition product (Scheme 1, pathway B). It is also understood that a substituent, (e.g., methyl) at the a carbon of allenoates can alter the inherent reactivity pattern of nonsubstituted allenoates. For example, under the catalysis of nucleophilic phosphanes, both activated olefins and imines can exclusively undergo g addition to a-methyl allenoates, resulting in [4+2] annulation reactions (Scheme 1, pathway C); for aldehydes no such reaction, with a-substituted allenoates, has been reported in the literature. Intrigued by these elegant studies, especially from the Kwon group, we suspected that the introduction of a substituent at the g carbon of an allenoate may be able to alter the normal regioselectivity of g addition of aldehydes to allenoates. Although it is known that g-substituted allenoates still retain similar reactivity patterns with activated olefins and imines to those of nonsubstituted allenoates. To evaluate this hypothesis, we began our investigation with allenoates bearing a small substituent like methyl (2 a) or a bulky substituent like phenyl (2 b) or tertiary butyl (2 c) at the g carbon. The preliminary experimental results showed that in the presence of PPh3 (20 mol%) the reaction of gmethyl allenoate (2 a) and o-chlorobenzaldehyde (1 a) proceeded smoothly to give the new products (3 a, 4 a, and 5 a) in appreciable yields (Scheme 2). Under similar conditions, however, neither g-phenyl nor g-tert-butyl allenoates afforded any new products. Clearly 3 a, 4 a, and 5 a were formed by unprecedented reaction pathways. The tetrahydrofuran derivative 3 a is indeed the product of a [3+2] annulation, resulting from the incorporation of three carbons of the allenoate with the carbonyl of the aldehyde; the g-methyl of 2 a is directly involved in the carbon–carbon bond-forming [a] S. Xu, L. Zhou, R. Ma, Prof. Dr. H. Song, Prof. Dr. Z. He The State Key Laboratory of Elemento-Organic Chemistry and Department of Chemistry, Nankai University 94 Weijin Road, Tianjin 300071 (China) Fax: (+86) 22-23501520 E-mail : zhengjiehe@nankai.edu.cn Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200901276.
104 citations
TL;DR: Implementation of an enantioselective Michael addition followed by an intramolecular aldol reaction catalyzed by two phosphoric acids has enabled the synthesis of cyclohexenone derivatives with excellent enantiOSElectivities.
Abstract: Let's resolve our differences: Implementation of an enantioselective Michael addition followed by an intramolecular aldol reaction catalyzed by two phosphoric acids has enabled the synthesis of cyclohexenone derivatives with excellent enantioselectivities. Prominent kinetic resolution was observed in the latter reaction. Ar = aromatic group, X = H, halogen, Y = H, Me, halogen.
TL;DR: A stereocontrolled synthesis of a complex pentacycle embodying the molecular architecture of the cortistatin class of natural products was achieved from the (+)-Hajos-Parrish ketone using a hypervalent iodine induced tandem intramolecular oxidative dearomatization and nitrile oxide cycloaddition.
TL;DR: All pyrido[1,2-a]benzimidazoles, polysubstituted benzenes, poly SubStituted indoles, and some key reaction intermediates are characterized by (1)H and (13)C NMR, MS, IR spectra, and elemental analysis as well as X-ray crystallography.
Abstract: Polysubstituted pyrido[1,2-a]benzimidazole derivatives are efficiently produced in moderate yields in a novel one-pot, four-component reaction from pyridine or 3-picoline, chloroacetonitrile, malononitrile, and aromatic aldehyde in refluxing acetonitrile. The mechanism of this novel reaction was believed involving the formation of polysubstituted benzenes with subsequent substitution and annulation reaction of pyridine. All pyrido[1,2-a]benzimidazoles, polysubstituted benzenes, polysubstituted indoles, and some key reaction intermediates are characterized by 1H and 13C NMR, MS, IR spectra, and elemental analysis as well as X-ray crystallography.
TL;DR: 3-Sulfenylindoles can be efficiently prepared in moderate to good yields from 2-(1-alkynyl)benzenamines and disulfides using the palladium/ air catalytic systems and provides a useful route to the synthesis of fipronil analogues.
Abstract: 3-Sulfenylindoles can be efficiently prepared in moderate to good yields from 2-(1-alkynyl)benzenamines and disulfides using the palladium/ air catalytic systems. The study also provides a useful route to the synthesis of fipronil analogues.
TL;DR: This work reports the first example that [4 + 2]-cycloadducts are successfully intercepted from such functionalities in diversified approaches, and the value of such cycloadditions and annulations are shown by their high diastereoselectivity and chemoselectivities.
Abstract: We report stereoselective synthesis of tricyclic ketals through Pt(II)-catalyzed [4 + 2]-cycloaddition of benzopyrilium/1-en-3-ol functionalities. For nonaromatic enynals, we obtained distinct tricyclic oxacyclic ketones due to occurrence of a new annulation reaction. This work reports the first example that [4 + 2]-cycloadducts are successfully intercepted from such functionalities in diversified approaches. The value of such cycloadditions and annulations are shown by their high diastereoselectivities and chemoselectivities.
TL;DR: Construction of four contiguous stereocenters in a stereoselective manner is noteworthy inhomoenolates generated from enals by nucleophilic heterocyclic carbene (NHC) catalysis.
TL;DR: An efficient synthesis of 3-chalcogen-benzo[b]furans via palladium-promoted annulation reactions of 2-alkynylphenol derivatives with disulfides or diselenides and iodide has been developed.
Abstract: An efficient synthesis of 3-chalcogen-benzo[b]furans via palladium-promoted annulation reactions of 2-alkynylphenol derivatives with disulfides or diselenides and iodide has been developed. In the presence of I(2) and PdCl(2), both 3-sulfenylbenzofurans and 3-selenenylbenzofurans were selectively prepared from the cyclization of 2-alkynyanisoles with disulfides or diselenides in moderate to excellent yields.
TL;DR: The annulation of thiadiazole to anthracene gives a stable material with optical properties similar to those of substituted pentacenes, which displays attractive optical and electrochemical properties.
TL;DR: A phosphine-catalyzed [3+3] annulation reaction of modified tert-butyl allylic carbonates with various alkylidenemalononitriles to form cyclohexenes was developed in this article.
TL;DR: The direct Pd-catalyzed intramolecular rapidly with electron-deficient benzene ring together with cascade intermolecular arylation allowed for efficient synthesis of fully-substituted fluorenes 12, the products of 5-exo-dig cyclization, in excellent yields.
Abstract: The direct Pd-catalyzed intramolecular rapidly with electron-deficient benzene ring, which, in hydroarylation of o-alkynyl biaryls proceeded in highly combination with a substantial isotope effect observed, stereoselective manner producing fluorenes 2, the products of 5-exo-dig cyclization, in excellent yields. The cascade intermolecular arylation, incorporated in this transformation, allowed for efficient synthesis of fully-substituted fluorenes 12. These cyclizations proceed more rapidly with electron-deficient benzene ring, which, in combination with a substantial isotope effect observed, strongly supports a C-H activation mechanism for the key annulation step.
TL;DR: An interesting gold-catalyzed electrophilic addition to arylalkyne to synthesize substituted naphthalenes has been presented and counter anion and oxo- and alkynophilicities of catalytic gold species might play an important role in this annulation reaction.
TL;DR: The scope of this methodology is extended by using the resulting 2-perfluoroalkyl-3-iodo quinolines in Suzuki, annulation, dehalogenation and carboxylation reactions.
Abstract: A series of highly substituted 2-perfluoroalkyl-3-iodoquinolines are prepared by two different methods in good to excellent yields under mild reaction conditions. The first method involves iodocyclization of perfluoroalkyl propargyl imines with I2-CAN. The second method involves iodocyclization of perfluoroalkyl propargyl amines using I2 and ICl. The perfluoroalkyl propargyl amines are prepared in excellent yields viaSonogashira coupling of easily accessible imidoyl iodides with alkynes followed by reduction with NaBH3CN. The scope of this methodology is extended by using the resulting 2-perfluoroalkyl-3-iodo quinolines in Suzuki, annulation, dehalogenation and carboxylation reactions. Antimalarial activity of the 2-perfluoroalkyl-3-iodoquinolines is discussed.
TL;DR: A general procedure for the palladium-catalyzed annulation of substituted haloanilines with norbornadiene gives functionalized indolines in 51-98% yield and extension to the use of substituted halobenzamides gives functionalizing isoquinolinones in up to 86% yield.
Abstract: A general procedure for the palladium-catalyzed annulation of substituted haloanilines with norbornadiene gives functionalized indolines in 51-98% yield. These indolines can be rapidly converted to benzenoid-substituted indoles and tricyclic indolines. Extension to the use of substituted halobenzamides gives functionalized isoquinolinones in up to 86% yield.
TL;DR: In this article, a ZnBr2-mediated arylation of aryl/heteroaryl methyl bromides with arenes at 80 °C led to the formation of the arylated products, which underwent subsequent 1,5 sigmatropic rearrangement followed by electrocyclization and aromatization with loss of a diethylmalonate unit to afford the corresponding annulated products.
TL;DR: Brønsted acids catalyze the addition of enolizable beta-diketones, beta-ketoesters, and vinylogous amides to alpha,beta-unsaturated aldehydes to lead to substituted chromenones, pyranones, and tetrahydroquinolinones in good yields under mild reaction conditions via a formal [3 + 3] cycloaddition.
Abstract: Bronsted acids catalyze the addition of enolizable beta-diketones, beta-ketoesters, and vinylogous amides to alpha,beta-unsaturated aldehydes to lead to substituted chromenones, pyranones, and tetrahydroquinolinones in good yields under mild reaction conditions via a formal [3 + 3] cycloaddition.
TL;DR: The first total synthesis of (−)-himandrine, a member of the class II galbulimima alkaloids, was described in this article, where a diastereoselective Diels−Alder reaction was used in the rapid synthesis of the tricycle ABC-ring system in an enantiomerically enriched form.
Abstract: We describe the first total synthesis of (−)-himandrine, a member of the class II galbulimima alkaloids. Noteworthy features of this chemistry include a diastereoselective Diels−Alder reaction in the rapid synthesis of the tricycle ABC-ring system in an enantiomerically enriched form, the use of a formal [3+3] annulation strategy to secure the CDE-ring system with complete diastereoselection, and successful implementation of our biogenetically inspired oxidative spirocyclization of an advanced intermediate. The successful and direct late-stage formation of the F-ring in the hexacyclic core of himandrine drew on the power of biogenetic considerations and fully utilized the inherent chemistry of a plausible biosynthetic intermediate.
TL;DR: In this paper, the intramolecular cyclisation of 2-acetyl-1-propargylpyrroles and 2-alkynylbenzaldehydes, respectively, in the presence of ammonia under microwave heating was achieved.
TL;DR: The N-heterocyclic carbene (NHC)-catalyzed annulation of enals with nitroso compounds in the presence of DBU in THF has been described.
Abstract: The N-heterocyclic carbene (NHC)-catalyzed annulation of enals with nitroso compounds in the presence of DBU in THF has been described. Unexpected seven-membered 4-azalactones were formed according to a process involving a 1,2-Bamberger-type rearrangement.
TL;DR: The enantioselective synthesis of stereochemically and structurally diverse spirocyclic oxindoles by [5 + 2]-annulation of chiral crotylsilanes bearing a primary alcohol is described.