Top PDF Palladium catalyzed annulation of internal alkynes

Palladium catalyzed annulation of internal alkynes

Palladium catalyzed annulation of internal alkynes

Palladium catalyzed annulation of internal alkynes Abstract A method is provided for the regioselective, palladium catalyzed carbo- or heteroannulation of internal alkynes by aryl iodide[r]

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Regioselective Access to Sultam Motifs through Cobalt Catalyzed Annulation of Aryl Sulfonamides and Alkynes using an 8 Aminoquinoline Directing Group

Regioselective Access to Sultam Motifs through Cobalt Catalyzed Annulation of Aryl Sulfonamides and Alkynes using an 8 Aminoquinoline Directing Group

In order to further compare the reactivities of the substrates under the optimized protocol, we performed intermolecular competition reactions (Scheme 3). When two equivalents of both a terminal (a) and internal (g) alkyne were included it was found that insertion of the terminal alkyne was significantly favored, resulting in a product ratio of 15:1 for terminal and internal alkyne insertion respectively (Scheme 3.1). Thereafter we also ran competition reactions using differently substituted aryl sulfonamide and phenylacetylene substrates (Scheme 3.2 and 3.3 respectively). As expected, in agreement with the results obtained from the substrate scoping, reaction with electron-donating aryl sulfonamides (methoxy, 1b) was found to be slightly favored over electron-withdrawing (chloro, 1c) aryl sulfonamides. Likewise, insertion of the p-nitro phenylacetylene (n) was favored over p-methoxy phenylacetylene (j). The latter competition reaction only yielded 34% of the p- nitro product (1an), whereas in the absence of the competing p-methoxy phenylacetylene during substrate scoping we obtained 97% isolated yield. This result suggests that the p-methoxy phenylacetylene is inhibiting the reaction to some extent. This inhibition is similar to the result obtained by Ackermann and co-workers during their intermolecular competition reactions. [6r]
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Synthesis of spirocyclic enones by rhodium catalyzed dearomatizing oxidative annulation of 2 alkenylphenols with alkynes and enynes

Synthesis of spirocyclic enones by rhodium catalyzed dearomatizing oxidative annulation of 2 alkenylphenols with alkynes and enynes

T he heteroatom-directed C‒H functionalization [ 1 ] of aromatic C(sp 2 )‒H bonds with alkynes has become a versatile and conceptually attractive approach for the synthesis of a diverse range of heterocyclic compounds. [ 2 – 4 ] We have recently explored enol-directed catalytic oxidative annulations that provide carbocyclic, rather than heterocyclic products, and have demonstrated the ruthenium-, rhodium-, or palladium-catalyzed formation of spiroindenes from 2-aryl cyclic-1,3-dicarbonyl compounds and alkynes (Scheme 1a). [5] Given the electronic similarity between the enol group of cyclic 1,3-dicarbonyls and the hydroxyl group of phenols, and the broad significance of phenols as chemical building blocks, we became interested in the use of 2-alkenylphenols in dearomatizing oxidative spiroannulations (Scheme 1d). [6] This process would provide spirocyclic enones, the basic ring system of which appears in several natural products (Figure 1). [7]
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Z-selective dimerization of aromatic terminal alkynes catalyzed by an iridium(I) n-heterocyclic carbene-phosphine system

Z-selective dimerization of aromatic terminal alkynes catalyzed by an iridium(I) n-heterocyclic carbene-phosphine system

Abstract: The development of an iridium-catalyzed regio- and ste- reoselective dimerization process has enabled the formation of (Z)- enyne products. More specifically, low catalyst loadings of an irid- ium(I) complex, featuring a bulky N-heterocyclic carbene–phos- phine ligand combination, has been successfully employed in this selective head-to-head dimerization of terminal alkynes via C–H activation.

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Applications of Palladium-Catalyzed Enantioselective Decarboxylative Alkylation in Natural Products Total Synthesis

Applications of Palladium-Catalyzed Enantioselective Decarboxylative Alkylation in Natural Products Total Synthesis

Hayashi pioneered this type of reaction during an exploration of Pd-catalyzed alkylation of β -dicarbonyls (Scheme 1.6). 22 Investigations revealed ferrocenyl catalyst 42 as a superior ligand for the transformation of 43 to 44. Diverse substrates were screened, and most displayed only limited stereoselectivity. Ultimately, allyl diketone 44 was prepared in a maximum 81% ee. Other activated carbonyl compounds including but not limited to 45, 46, 47, and 48 were also accessible, with modest degrees of enantioselectivity. Optical activity was observed for 7-membered ring substrates, but 5-membered ring examples displayed very low stereoselectivity. Inspired by Hayashi’s work, Ito also investigated these enantioselective alkylations using a crown-ether-modified phosphinoferrocenes with modest success. 23
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Palladium-catalyzed borylation of aryl (pseudo)halides and its applications in biaryl synthesis

Palladium-catalyzed borylation of aryl (pseudo)halides and its applications in biaryl synthesis

of the boronic ester intermediates was required nor was catalyst added prior to conducting the cross-coupling step. As illustrated by the examples summarized in Table  3, both aryl chlorides and bromides performed well whether used as borylated substrates or electro- philic coupling partners in the reaction. Aryl halides with electron-donating groups such as hydroxyl, alkyl and methoxyl (Table  3, entries 3, 6–8), electron-withdraw- ing groups such as aldehyde and trifluoromethyl (Table 3, Table 2 Palladium-catalyzed borylation of aryl (pseudo)halides

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Palladium catalyzed coupling of aryl halides, non conjugated dienes and carbon nucleophiles

Palladium-catalyzed coupling of aryl halides, non-conjugated dienes and carbon nucleophiles

Palladium-catalyzed coupling of aryl halides, non-conjugated dienes and carbon nucleophiles Abstract The present invention provides a method for the alpha,omega-arylation/alkylation of a[r]

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Part I: Chemoselective Palladium Catalyzed Reactions of Bifunctional 2-B(pin)-Substituted Allylic Acetate Derivatives Part II: Palladium Catalyzed Deprotonative Arylation of Azaarylmethyl Amines and Ethers

Part I: Chemoselective Palladium Catalyzed Reactions of Bifunctional 2-B(pin)-Substituted Allylic Acetate Derivatives Part II: Palladium Catalyzed Deprotonative Arylation of Azaarylmethyl Amines and Ethers

high yields of 1,3-disubstituted allenes under mild conditions. While the allene formation reaction of enantioenriched 2-B(pin) allylic acetate provided the enantioenriched allene, palladium-catalyzed racemization of the allene resulted in the racemic product over time. With the ability to control chemoselectivity, various tandem reactions were investigated. The allylic substitution of 2-B(pin)-substituted allylic acetates can be followed with a Suzuki-Miyaura cross-coupling to afford (E)-trisubstituted allylic amines and malonates with four points of diversity. Enantioenriched 2-B(pin)-substituted allylic acetates undergo allylic substitution with net stereochemical retention, allowing isolation of B(pin)-containing substitution products or α- amino ketones with little or no loss of ee. Alternatively, the allylic substitution of 2-B(pin)- substituted allylic acetates can be paired with oxidation of vinyl boronates to provide valuable α-amino ketones and 1,4-dicarbonyl compounds.
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Palladium-catalyzed synthesis of aryl amides through silanoate-mediated hydrolysis of nitriles

Palladium-catalyzed synthesis of aryl amides through silanoate-mediated hydrolysis of nitriles

selected for use in all screening reactions, so as to avoid the necessary reduction of Pd(II) catalysts, at an initial loading of 5 mol%. From this study, it was determined that the palladium catalyzed conversion of the benzonitrile adduct 2 to anilide 3 could be achieved as shown in Scheme 2, providing proof of principle that imidate species such as 2 were capable of undergoing Buchwald-Hartwig arylation.

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Ultrasonic Activation of Suzuki and Hiyama Cross Coupling Reactions Catalyzed by Palladium

Ultrasonic Activation of Suzuki and Hiyama Cross Coupling Reactions Catalyzed by Palladium

The analysis of the results in Table 2 reveals that the Suzuki coupling reaction catalyzed by palladium using 1a by magnetic stirring at 100 ˚C did not occur in the absence of a base. Therefore, the yield was found to depend on the nature of the base used. This is in line with previous findings [5]. Besides, the various bases studied are of the type: Et 3 N, NaOH, KOH, Na 2 CO 3 , K 2 CO 3 , Cs 2 CO 3 , K 3 PO 4 (Table 2). The reactivity increased with the ad-

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Aqueous Phase, Palladium Catalyzed Suzuki Reactions under Mild Conditions

Aqueous Phase, Palladium Catalyzed Suzuki Reactions under Mild Conditions

We initially focused on the Pd-catalyzed coupling reac- tion of phenyl boronic acid with phenyl iodide in the presence of diol-functionalized IL, 1. The previous studies [19] observed that the choice of solvent was very important for the reaction. Water represents one of the most economically and environmentally viable options. However, catalysts gave low activities when the reaction was carried out in neat water due to the low solubility of phenyl iodide in water. Therefore, 1:1 CH 3 CN/H 2 O was

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Palladium Catalyzed Decarboxylative and Decarbonylative Transformations in the Synthesis of Fine and Commodity Chemicals

Palladium Catalyzed Decarboxylative and Decarbonylative Transformations in the Synthesis of Fine and Commodity Chemicals

Importantly, enolate stabilization is critical for success in both of these catalytic systems, thereby limiting the scope of each transformation. To the best of our knowledge, there are no examples of catalytic asymmetric alkylations of simple piperidinone, pyrrolidinone, and caprolactam scaffolds for the formation of C(α)- quaternary or C(α)-tetrasubstituted tertiary centers. Herein, we describe the stereoselective synthesis of a wide range of structurally-diverse, functionalized lactams by palladium-catalyzed enantioselective enolate alkylation. The importance of this chemistry to the synthesis of bioactive alkaloids is specifically demonstrated, and the potential utility of this transformation for the construction of novel building blocks for medicinal and polymer chemistry can be readily inferred.
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Palladium catalyzed ring opening of meso bicyclic hydrazines with catechol and resorcinol

Palladium catalyzed ring opening of meso bicyclic hydrazines with catechol and resorcinol

A novel method for the synthesis of disubstituted cyclopentenes with phenolic hydroxyl group has been investigated. This methodology involves the palladium catalyzed ring opening of azabicyclichydrazines with catechols and resorcinolthatlead to the formation of 1,4-disubstituted cyclopentenes with potent phenolic hydroxyl group. This method is useful for synthesis of benzoquinone appended cyclopentenes, which are known to be highly bioactive molecules.

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New Heat Resistant and Soluble Aramids Synthesized by
Palladium Catalyzed Carbonylation Polycondensation

New Heat Resistant and Soluble Aramids Synthesized by Palladium Catalyzed Carbonylation Polycondensation

in Table 2. We avoided using protic solvent such as al- cohols to exclude the possibility that undesired nucleophile could participate in the carbonylation-polycondensation and terminate the polymerization. Although the aminolysis of acyl-palladium intermediate is expected to be favorable in polar solvent, the solubility of product is more important factor than the polarity of solvent in our case. Aramid 3a was found to be easily dissolved in aprotic polar solvents such as DMA, dimethyl sulfoxide (DMSO), DMF, and 1,3- dimethyl-2-imidazolidone (DMI), and these solvents medi- ated the polymerization very well. The efficiency of these solvents may be due to good solubility of aramids in them.
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Following palladium catalyzed methoxycarbonylation by hyperpolarized NMR spectroscopy : A: para hydrogen based investigation

Following palladium catalyzed methoxycarbonylation by hyperpolarized NMR spectroscopy : A: para hydrogen based investigation

We therefore suggest in 10 that CO binding to the fourth site occurs, and that the palladium centre is charged, which means that an out-of-plane cis-stilbene ligand is indicated (Figure 5). The signals of 10, alongside those of 2 and cis– stilbene itself, become more evident as the samples temperature is raised and overtime, the enhanced hydride signal of 5 appears in the associated NMR spectra. Studies by Parker et al. have suggested that the alkenes of such species could be labile and it is therefore not surprising that complexes of this type are only detected here through a hyperpolarised response. 71
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Palladium(II)-Catalyzed Oxidation Reactions in Natural Product Synthesis: Efforts toward Bielschowskysin and Phalarine

Palladium(II)-Catalyzed Oxidation Reactions in Natural Product Synthesis: Efforts toward Bielschowskysin and Phalarine

Two types of oxidative transformations, an oxidative kinetic resolution and an oxidative heterocyclization, have been developed by several laboratories using palladium(II)-catalysis to provide enantioenriched products. The main drawback of these asymmetric transformations is the limited substrate scope for each set of conditions. To address this, the Stoltz laboratory developed a unique platform utilizing palladium(II)- catalysis that provides a highly effective oxidative kinetic resolution of secondary alcohols and an asymmetric oxidative heterocyclization of phenols. Key to this platform is the use of (–)-sparteine as the chiral ligand and O 2 as the stoichiometric oxidant. Both
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Palladium-Catalyzed C-C Bond and C-S Bond Forming Reactions of Sulfoxides

Palladium-Catalyzed C-C Bond and C-S Bond Forming Reactions of Sulfoxides

with LiO t Bu and CPME by testing a series of sterically and electronically diverse mono- and bi-dentate ligands. Of the 112 ligands examined, 1.L2–1.L5 14 were promising (see Experiment Section for details), with N-(dicyclohexylphosphino)-2-2'-tolylindole (1.L2) outperforming the others (Table 1-1, entry 3 vs. 4–6). To the best of our knowledge, this monodentate, bulky, and electron-rich phosphine ligand, introduced by Kwong and coworkers, has only been successfully employed in one study of the Suzuki-Miyaura cross-coupling reaction. 14b The microscale result using 1.L2 was successfully translated to laboratory scale, rendering product 1.3a in 75% isolated yield. A decrease in temperature (entry 7) or catalyst/ligand loading (entry 8) was detrimental to the yield under these conditions. We next focused on the identification of more suitable palladium sources, substrate ratios, and temperatures. Of the conditions and ratios examined, better results for the direct alpha arylation were obtained on microscale employing Pd(OAc) 2 (10 mol %),
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Palladium-Catalyzed Borylation And Cross-Coupling Of Aryl And Heteroaryl Halides Utilizing Dibora Derivatives

Palladium-Catalyzed Borylation And Cross-Coupling Of Aryl And Heteroaryl Halides Utilizing Dibora Derivatives

The Suzuki-Miyaura cross-coupling of boronic acids with organic halides is one of the most widely applied methods in current synthetic organic chemistry. 1,2 Since the first report of the palladium-catalyzed cross-coupling between an aryl halide and an arylboronic acid by Suzuki and Miyaura in 1981, 3 it has emerged as a functional group tolerant method, providing reliable and efficient access to structurally diverse biaryl motifs. 4 It is for these reasons that it remains one of the most important methods of choice for C-C bond formation in industrial and academic groups alike. Fueled by the commercial availability of numerous organic halides, boronic acids, and the constant development of improved catalyst systems, 5,6 rather intense research efforts continue in this area.
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Studies in Palladium-Catalyzed Allylic Alkylation: Enantioselective Total Syntheses of Structurally Diverse Alkaloids

Studies in Palladium-Catalyzed Allylic Alkylation: Enantioselective Total Syntheses of Structurally Diverse Alkaloids

The authors then expertly used the single stereocenter in 104 to build the three remaining rings and complete their synthesis of (–)-aspidophytine (10) in a stereoselective fashion (Scheme 1.4.5.2). A four-step sequence effected ketone and azide reduction along with amine protection and a Pictet–Spengler-type cyclization to deliver cis-fused tetracycle 105. Global deprotection is followed by regioselective alkylation using 2-bromoethanol furnished aminoalcohol 106. Pyrrolidine annulation and selenoxide elimination gave α,β-unsaturated imine 107, which could undergo hydride reduction and reductive amination in the same pot to yield penultimate N-methyl indoline 108. This intermediate was converted to (–)-aspidophytine (10) by adapting a two-step protocol reported by Corey. 65
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Highly Enantioselective Palladium Catalyzed Allylic Alkylation Reactions of Carbocyclic Enaminones and Acyclic Substrates

Highly Enantioselective Palladium Catalyzed Allylic Alkylation Reactions of Carbocyclic Enaminones and Acyclic Substrates

we reported the preparation of !-quaternary cyclic ketones from allyl enol carbonates 9 and silyl enol ethers 10.6a Twenty years prior, Tsuji performed the regioselective allylation of t[r]

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