Showing papers on "Annulation published in 2012"
TL;DR: Taking advantage of Rh(III)-catalyzed C-H activation reactions, a mild, short, and efficient method for the synthesis of bench-stable 3-isoquinolone MIDA boronates is developed.
Abstract: Taking advantage of Rh(III)-catalyzed C–H activation reactions, we have developed a mild, short, and efficient method for the synthesis of bench-stable 3-isoquinolone MIDA boronates. The reaction is practical and scalable. The product formed has been applied in the Suzuki–Miyaura reaction with high efficiency. This strategy has also been successfully expanded to the synthesis of MIDA boronate functionalized heterocycles such as isoquinoline, pyrrole, and indole.
334 citations
TL;DR: A novel Rh(III)-catalyzed oxidative coupling with allenes under mild conditions provides heterocycles with exocyclic double bonds that features low catalyst loadings, high regio- and stereoselectivity, and excellent substrate scope.
Abstract: All(enes) great! A novel Rh(III)-catalyzed oxidative coupling with allenes under mild conditions provides heterocycles with exocyclic double bonds. This reaction features low catalyst loadings, high regio- and stereoselectivity, and excellent substrate scope. The products were derivatized and preliminary mechanistic studies were conducted.
309 citations
TL;DR: This novel reaction provides a facile route to synthesize indenones from readily available benzimides and internal alkynes.
Abstract: Doubled up: a rhodium(III)/copper(II) system co-catalyzes the annulation of benzimides with internal alkynes for the synthesis of indenones (see scheme; Cp*=C(5) Me(5)). The reaction involves an uncommon nucleophilic addition of a transition-metal-carbon bond to an imide moiety. This novel reaction provides a facile route to synthesize indenones from readily available benzimides and internal alkynes.
278 citations
TL;DR: This article focuses on the important developments concerning asymmetric annulations of allenes with unsaturated partners in the recent decades and on the perspectives that these new developments offer.
262 citations
TL;DR: A manganese-mediated annulation of 2-isocyanobiaryls with organoboronic acids is developed for the synthesis of a broad range of phenanthridine derivatives and Mechanistic studies indicate that the reaction proceeds by the intramolecular homolytic aromatic substitution of an imidoyl radical intermediate.
Abstract: Where HAS you been? A manganese-mediated annulation of 2-isocyanobiaryls with organoboronic acids is developed for the synthesis of a broad range of phenanthridine derivatives. Mechanistic studies indicate that the reaction proceeds by the intramolecular homolytic aromatic substitution (HAS) of an imidoyl radical intermediate.
262 citations
TL;DR: The mild, efficient, and practical intramolecular rhodium-catalyzed C-H/N-H bond functionalization reaction provides isoquinolones with a reverse regioselectivity compared to the reported intermolecular version.
Abstract: The mild, efficient, and practical intramolecular rhodium-catalyzed C—H/N—H bond functionalization reaction provides isoquinolones with a reverse regioselectivity compared to the reported intermolecular version.
254 citations
TL;DR: A cooperative catalysis approach for the enantioselective formal [3+2] addition of α,β-unsaturated aldehydes to isatins has been developed and has been used for the total synthesis of maremycin B.
Abstract: A cooperative catalysis approach for the enantioselective formal [3+2] addition of α,β-unsaturated aldehydes to isatins has been developed. The N-heterocyclic carbene (NHC)-catalyzed homoenolate annulations of β-aryl enals require the addition of lithium chloride for high levels of enantioselectivity. This NHC-catalyzed annulation provides efficient access to the 3-hydroxy indole skeleton and has been applied to the first eantioselective total synthesis of maremycin B.
244 citations
238 citations
TL;DR: The cascade oxidative annulation reactions of benzoylacetonitrile with internal alkynes proceed efficiently in the presence of a rhodium catalyst and a copper oxidant to give substituted naphtho[1,8-bc]pyran products, which exhibit intense fluorescence in the solid state.
Abstract: The cascade oxidative annulation reactions of benzoylacetonitrile with internal alkynes proceed efficiently in the presence of a rhodium catalyst and a copper oxidant to give substituted naphtho[1,8-bc]pyrans by sequential cleavage of C(sp2)–H/C(sp3)–H and C(sp2)–H/O–H bonds. These cascade reactions are highly regioselective with unsymmetrical alkynes. Experiments reveal that the first-step reaction proceeds by sequential cleavage of C(sp2)–H/C(sp3)–H bonds and annulation with alkynes, leading to 1-naphthols as the intermediate products. Subsequently, 1-naphthols react with alkynes by cleavage of C(sp2)–H/O–H bonds, affording the 1:2 coupling products. Moreover, some of the naphtho[1,8-bc]pyran products exhibit intense fluorescence in the solid state.
236 citations
TL;DR: The photocatalytic reaction of o-methylthio-arenediazonium salts with alkynes yields substituted benzothiophenes regioselectively through a radical annulation process through green light irradiation of eosin Y.
204 citations
TL;DR: The catalytic C-H coupling method employs cheaply available phenols and alcohols, exhibits a broad substrate scope, tolerates carbonyl and amine functional groups, and liberates water as the only byproduct.
Abstract: A well-defined cationic Ru–H complex catalyzes the dehydrative C–H alkylation reaction of phenols with alcohols to form ortho-substituted phenol products. Benzofuran derivatives are efficiently synthesized from the dehydrative C–H alkenylation and annulation reaction of phenols with 1,2-diols. The catalytic C–H coupling method employs cheaply available phenols and alcohols, exhibits a broad substrate scope, tolerates carbonyl and amine functional groups, and liberates water as the only byproduct.
TL;DR: An N-heterocyclic carbene (NHC)-catalyzed annulation reaction of isatin N-Boc ketimines and enals is developed for the synthesis of spirocyclic oxindole-γ-lactams bearing one quaternary chiral center in good yields and excellent stereoselectivities.
TL;DR: The success in using bidentate phosphine ligands to temper the reactivities of in situ-generated gold carbenes is likely to open many new opportunities to apply oxidative gold catalysis to the development of novel methods, and the implication of tricoordinated gold intermediates in homogeneous goldCatalysis should stimulate further advances ingold catalysis.
Abstract: 2,4-Oxazole is an important structural motif in various natural products. An efficient modular synthesis of this structure has been achieved via a [3 + 2] annulation between a terminal alkyne and a carboxamide using a gold-catalyzed oxidation strategy. The postulated reactive intermediate, a terminal α-oxo gold carbene, previously known to be highly electrophilic and hence unlikely to be trapped by stoichiometric external nucleophiles, is coerced to react smoothly with the carboxamide en route to the oxazole ring by a P,N- or P,S-bidentate ligand such as Mor-DalPhos; in stark contrast, often-used ligands such as monodentate phosphines and N-heterocyclic carbenes are totally ineffective. The role of these bidentate phosphines in this reaction is attributed to the formation of a tricoordinated gold carbene intermediate, which is less electrophilic and hence more chemoselective when reacting with nucleophiles. The success in using bidentate phosphine ligands to temper the reactivities of in situ-generated go...
TL;DR: A catalytic “cut-and-sew” reaction, which involves the oxidative addition of a transition metal to a C C bond (Scheme 1) is studied.
Abstract: Efficiency in the synthesis of a complex molecular target is greatly dictated by the strategy used for building the key skeletal structure. In particular, fused rings are extremely common structural motifs in natural products and drug molecules, and thus access to these motifs through selective and atom-economic methods is of significant importance. Despite the existence of various elegant stepwise cycloaddition methods for building fused-ring systems, we were particularly intrigued by a catalytic “cut-and-sew” reaction, which involves the oxidative addition of a transition metal to a C C bond (Scheme 1). In this type of reaction, a key intermediate, for example, metallocycle B, is formed when
TL;DR: Highly enantioselective annulation of activated alkenes with α-substituted allenoates catalyzed by amino acid-based bifunctional phosphines has been developed for the first time, which provides an easy access to optically enriched functionalized cyclohexenes.
Abstract: Highly enantioselective [4 + 2] annulation of activated alkenes with α-substituted allenoates catalyzed by amino acid-based bifunctional phosphines has been developed for the first time, which provides an easy access to optically enriched functionalized cyclohexenes. In particular, 3-spirocyclohexene-2-oxindoles were prepared in high yields and with excellent enantioselectivities.
TL;DR: A method for the synthesis of bi- and tricyclic amidines has been developed through copper-catalyzed aerobic [3+2]-annulation reaction of N-alkenyl amidines that could be converted into mono-benzyl-protected vicinal diamines by the reduction with aluminum hydride.
Abstract: A method for the synthesis of bi- and tricyclic amidines has been developed through copper-catalyzed aerobic [3+2]-annulation reaction of N-alkenyl amidines. These cyclic amidines could be converted into mono-benzyl-protected vicinal diamines by the reduction with aluminum hydride.
TL;DR: In an effort to explain why stable enols such as naphthol, kojic acid, and dicarbonyl are uniquely efficient, it is postulated that this annulation occurs via a Coates-Claisen rearrangement that invokes the formation of a hemiacetal prior to a sigmatropic rearrangements.
Abstract: A combination of a chiral N-heterocyclic carbene catalyst and α,β-unsaturated aldehyde leads to a catalytically generated α,β-unsaturated acyl azolium, which participates in a highly enantioselective annulation to give dihydropyranone products. This full account of our investigations into the scope and mechanism of this reaction reveals the critical role of both the type and substitution pattern of the chiral triazolium precatalyst in inducing and controlling the stereochemistry. In an effort to explain why stable enols such as naphthol, kojic acid, and dicarbonyl are uniquely efficient, we have postulated that this annulation occurs via a Coates–Claisen rearrangement that invokes the formation of a hemiacetal prior to a sigmatropic rearrangement. Detailed kinetic investigations of the catalytic annulation are consistent with this mechanistic postulate.
TL;DR: An efficient organocatalytic Michael-aldol cascade reaction for the asymmetric synthesis of spirocyclic oxindole derivatives fused with tetrahydrothiophenes has been developed through a formal [3+2] annulation strategy.
TL;DR: The selective oxidative fusion of 2-aminoanthracenes mediated by 2,3-dichloro-5,6dicyano-1,4-benzoquinone (DDQ) to provide pyrazine-fused bisanthracenes in high yields is disclosed, which makes use of the more-stable monoamino substrates and would be useful for the construction of various pyrazined oligoacenes.
Abstract: Aniline is oxidized into so-called “aniline black”, well-known black pigments that are a mixture of oligomeric materials containing C N double bonds and fused structures. Since such an oxidative fusion reaction of aniline derivatives is usually uncontrollable and provides many isomers and oligomers, it has rarely been recognized as a synthetically useful transformation. However, the selective oxidation of aromatic amines should provide a powerful protocol to combine two aromatic units into one extended p system if the substrates and reaction conditions are carefully designed. Recently, oligoacenes containing pyrazine units have attracted much attention as promising compounds for electron-transporting materials because of their resistance to oxidation relative to the parent oligoacenes. However, the synthetic strategy for this type of azaacenes has mainly been limited to the classic condensation of ortho-quinone derivatives with aromatic ortho-diamines, both of which are often unstable under air. Here we disclose the selective oxidative fusion of 2-aminoanthracenes mediated by 2,3-dichloro-5,6dicyano-1,4-benzoquinone (DDQ) to provide pyrazine-fused bisanthracenes in high yields. Our approach, which makes use of the more-stable monoamino substrates, would be useful for the construction of various pyrazine-fused oligoacenes. Furthermore, we also found that pyrrole-fused bisanthracenes could be formed under slightly modified conditions. The pyrrole-fused dimer can be regarded as an aza[7]helicene with a stable helical conformation that exhibits circular dichroism (CD) and circularly polarized luminescence (CPL) properties. We used 2-aminoanthracene 1a, the two triisopropylsilylethynyl groups of which enhance the solubility of the starting material and products. We found that the oxidation of 1a with DDQ in CHCl3 (Scheme 1) afforded a pyrazine-fused dimer 2a in 43 % yield as a single regioisomer (Table 1, entry 1). The H NMR spectrum of 2 a was indicative of a C2h symmetrical structure, thus indicating a zig-zag-type structure fused by a pyrazine linkage. Furthermore, another product 3a was obtained as a more polar material in 48 % yield. The H NMR spectrum showed 3a was unsymmetrical, with one NH proton signal detected at d = 9.12 ppm. The parent mass ion peaks of 3a at m/z = 1087.6716 (calcd for (C72H97NSi4) + = 1087.6693) suggested a loss of one nitrogen atom from 2a. On the basis of these data, we assigned 3a as a pyrrole-fused dimer. Finally,
TL;DR: An efficient method for the synthesis of substituted isoquinolinium salts from benzaldehydes, amines, and alkynes via ruthenium-catalyzed C-H bond activation and annulation in one pot is described.
TL;DR: An annulation via tandem rhodium catalyzed C-H olefination of N-benzoylsulfonamides with internal oleFins followed by C-N bond formation is disclosed, providing efficient access to a series of 3,3-disubstituted isoindolinones.
TL;DR: This reaction featuring C-H olefination and decarboxylative amination processes provides a concise access to C-2 arylated indolizines from simple and readily available starting materials.
TL;DR: A stereoselective [3+2] cycloaddition of isocyanoesters to methyleneindolinones catalyzed by a quinine-based thiourea-tertiary amine has been successfully developed and a variety of optically enriched 3,3'-pyrrolidinyl spirooxindole diastereomers could be obtained in excellent enantioselectivities.
TL;DR: The total synthesis of the terpene indole alkaloid (+)-ibophyllidine is performed through a pathway involving asymmetric phosphine catalysis, with the novel l-4-hydroxyproline-derived chiral phosphine mediating the key [3 + 2] annulation.
Abstract: In this study we performed the total synthesis of the terpene indole alkaloid (+)-ibophyllidine through a pathway involving asymmetric phosphine catalysis, with our novel L-4-hydroxyproline-derived chiral phosphine mediating the key [3 + 2] annulation. Hydrogenation of the [3 + 2] adduct allowed the rapid formation of the stereochemically dense pyrrolidine ring of (+)-ibophyllidine in excellent yield with exceptionally high levels of both diastereo- and enantioselectivity. We constructed the remainder of the pentacyclic skeleton through an intramolecular alkylation and an intramolecular aza-Morita–Baylis–Hillman reaction.
TL;DR: In the presence of chiral ScCl2(SbF6)·BIOP, prepared in situ, and TmsCl as an essential promoter, the desired spirooxindoles are obtained with excellent enantioselectivities at room temperature as mentioned in this paper.
Abstract: In the presence of chiral ScCl2(SbF6)·BIOP, prepared in situ, and TmsCl as an essential promoter, the desired spirooxindoles are obtained with excellent enantioselectivities at room temperature.
TL;DR: A new mode of catalytic alkyne oxidative annulation involving the (formal) functionalization of one Csp3 H bond and one CSP2 H bond is reported, which results in the formation of indenes, which are important structures in various biologically active compounds and functional materials.
Abstract: The metal-catalyzed oxidative annulation of alkynes with aryl or alkenyl substrates bearing various heteroatom-containing functional groups has proven to be a versatile, efficient, and atom-economic strategy to access a range of valuable heterocyclic products. These processes generally rely upon coordination of the metal center to the heteroatomcontaining functional group, which directs site selective Csp2 H bond cleavage to form the metallacycle A (Scheme 1a). Coordination and migratory insertion of the alkyne and subsequent C X (X = heteroatom) reductive elimination then forms the heterocyclic product. These alkyne oxidative annulations have been complemented by variants that result in the functionalization of two Csp2 H bonds, with or without the assistance of directing groups (Scheme 1b). While these reactions are effective in forming aromatic carboand azacycles, the scope and utility of the general process would be considerably enhanced if variants involving the functionalization of Csp3 H bonds could be developed, thus resulting in partially saturated cyclic products. However, progress in this area has been limited. To our knowledge, the only existing report comes from Nakao, Hiyama and co-workers, who recently described the oxidative annulation of formamides with alkynes, in which an extra equivalent of alkyne acts as the stoichiometric oxidant (Scheme 1c). Herein, we report a new mode of catalytic alkyne oxidative annulation involving the (formal) functionalization of one Csp3 H bond and one Csp2 H bond (Scheme 1d). This ruthenium-catalyzed process results in the formation of indenes, which are important structures in various biologically active compounds and functional materials. A notable feature of this process is the formation of an all-carbon quaternary center, which has not been described previously in alkyne oxidative annulations. At the outset of this work, we hypothesized that aarylcarbonyl compounds might be suitable substrates for alkyne oxidative annulations by virtue of the acidic nature of the a protons, that is, deprotonation would generate an enolate which could serve as an efficient directing group for Csp2 H bond cleavage. 2-Aryl cyclic 1,3-dicarbonyl compounds were selected for investigation on the basis of their high acidity and the permanent close proximity of the aryl and carbonyl groups. This latter feature renders these substrates conformationally predisposed for cyclometallation, thus forming a six-membered metallacycle in readiness for migratory insertion of the alkyne and spiroindene formation. 2-Aryl-1,3-diketones, which exist predominantly in the enol tautomer, were investigated first, and we began with a study of the reaction of 3-hydroxy-2-phenyl-2-cyclohexenone (1a) with 1-phenyl-1-propyne (2a ; Table 1). The Scheme 1. a)–d) Metal-catalyzed oxidative annulation of alkynes.
TL;DR: The present green synthesis of imidazo[1,2-a]pyridine derivatives shows fascinating properties such as high regioselectivity, concise one-pot methodology, short reaction times, easy purification and avoids the use of transition metals.
TL;DR: The first method for the [3 + 2] annulation of donor-acceptor aminocyclopropanes with aldehydes is reported and represents a stereoselective and atom economic access to valuable 2-aminotetrahydrofurans, which constitute the core of DNA and RNA.
TL;DR: A fragment-assembling strategy is used to form oxazoles from aryl acetaldehydes, amines, and molecular oxygen under mild conditions.
Abstract: A fragment-assembling strategy is used to form oxazoles from aryl acetaldehydes, amines, and molecular oxygen under mild conditions. The transformation is highly efficient with the removal of six hydrogen atoms, including the cleavage of four C(sp(3))-H bonds.
TL;DR: In this article, a three-component regioselective synthesis of 2-amino-3-cyano-4 H -chromene and tetrahydrobenzo[b ]pyran derivatives has been developed by annulation of aldehydes, malononitrile, and resorcinol or dimedone under reflux conditions in 2,2,2-trifluoroethanol without the use of a catalyst or any other additive.