Sterics versus Electronics: Regioselective Cross‐Coupling of Polybrominated Thiophenes

Amb, Chad M.; Rasmussen, Seth C.

doi:10.1002/ejoc.200701148

Cited by 24 publications

(28 citation statements)

References 21 publications

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Section: Resultsmentioning

confidence: 76%

“…As shown in Scheme , the π‐extended nickel thizaoledithiolene 8 was prepared in a similar manner to the previously reported nickel thiophenedithiolene 4 , , . The application of regioselective cross‐coupling methods developed for 2,3,5‐tribromothiophene to 2,4,5‐tribromothiazole ( 5 ) gave the intermediate 6 in reasonable yield, followed by conversion to the acetyl‐protected thiazoledithiolate ligand 7 . As previously discussed in detail, the specified sequential addition steps in the generation of the acetyl‐protected ligands are necessary to inhibit the halogen dance reaction, typical of lithiated thiophenes and their heterocyclic analogues.…”

Section: Resultsmentioning

confidence: 76%

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Thiophene‐Extended Nickel Thiazoledithiolene: π‐Extended Fused‐Ring Metal Dithiolenes with Stabilized Frontier Orbitals

Uzelac

Rasmussen

2017

Eur J Inorg Chem

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The preparation of tetrabutylammonium bis[2‐(2‐thienyl)‐4,5‐thiazoledithiolato]nickelate(1–) is presented as the first example of a new family of π‐extended fused‐ring metal dithiolenes. The optical, electronic, and structural properties of this complex have been characterized by UV/Vis‐NIR spectroscopy, cyclic voltammetry, and X‐ray crystallography. Comparison of these properties to the analogous nickel thiophenedithiolene shows that incorporation of nitrogen into the fused ring stabilizes the frontier orbitals of the thiazole‐based complex, while preserving the planar geometry, electronic delocalization, and low‐energy NIR absorption of the previous thiophene‐based species.

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Section: Resultsmentioning

confidence: 76%

Section: Resultsmentioning

confidence: 76%

Thiophene‐Extended Nickel Thiazoledithiolene: π‐Extended Fused‐Ring Metal Dithiolenes with Stabilized Frontier Orbitals

Uzelac

Rasmussen

2017

Eur J Inorg Chem

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“…Four series of novel selenophene‐core compounds, shown in Schemes –, were prepared from selenophene according to the synthetic procedures established in our research group for producing thiophene‐core ER ligands. In the synthesis of compounds 2 a – j (Scheme A), key intermediates 1 a – j were obtained by the Suzuki cross‐coupling of aryl boronic acid with 2,5‐dibromoselenophene 9 in the presence of sodium carbonate and 1,1′‐bis(diphenylphosphino)ferrocene (dppf)‐coordinated palladium chloride as a catalyst at reflux . The key intermediate selenophene precursor, 9 , was prepared by bromination of the selenophene using N ‐bromosuccinimide (NBS).…”

Section: Resultsmentioning

confidence: 99%

“…OBHS hydrogen bonds to the conserved Glu353 and Arg394 residues. The phenyl sulfonate extends outward between helices 8 and 11 . C) Computer‐developed model of 2 f bound to ERα with conserved hydrogen bonding to Glu353 and Arg394.…”

Section: Resultsmentioning

confidence: 99%

“…We recently reported on the crystal structure of oxabicyclic compound OBHS, where one of phenols, which mimics the role of A‐ring phenol of E 2 , engages in strong hydrogen bonding with the helix 3 residue Glu353 and the helix 6 residue Arg394. Beyond this, however, the large nonpolar phenyl sulfonate group in OBHS extends between helices 8 and 11, into a region in which it makes strong steric clashes with helix 11 and indirectly modulates the conformation of the critical helix 12 (Figure B), giving it partial antagonist activity, but limited agonist activity …”

Section: Resultsmentioning

confidence: 99%

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Selenophenes: Introducing a New Element into the Core of Non‐Steroidal Estrogen Receptor Ligands

Zhang

Wang

et al. 2017

ChemMedChem

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The importance of the heterocyclic core elements with peripheral phenolic and alkyl substituents as a dominant structural motif of ligands for estrogen receptor (ER) has been well recognized. Here, we expand the structural diversity of core elements by preparing selenium-containing heterocycles and exploring the activities of these selenophenes on the two ERs, ERα and ERβ. Careful structure-activity relationship analysis of their ER binding affinities showed that most selenophenes are ERβ-selective, with the position of the phenol substituents on the selenophenecore and the nature of these substituents having in a marked effect on their binding affinities. The compound bis(2-fluoro-4-hydroxyphenyl)selenophene (2f) has the highest relative binding affinity (RBA) of 24.3 for ERβ. In transcription assays, most of selenophenes exhibit partial to full agonist activity for both ER subtypes, with compounds bis(2-methyl-4-hydroxyphenyl)selenophene (2b), bis(4-fluoro-3-hydroxyphenyl) 3-bromoselenophene (6f), 2,3,5-tris(hydroxyphenyl)-thiophenes (8b and 8d) profiling as superagonists for ERα, but several compounds display a range of ERα or ERβ antagonistic activities. A few selenophenes exhibited antiproliferative activity, with compound 8c showing antiproliferative effects comparable to that of 4OHT in breast cancer MCF-7 cells while being nontoxic to normal VERO cells. These new ligands could act as models for the development of novel agents leading to improved therapeutics that target the estrogen receptor. Add a New Element!Correspondence to: Jian Huang; Hai-Bing Zhou. ‡ These two authors contributed equally to this work Supporting information for this article is given via a link at the end of the document. HHS Public Access Author ManuscriptAuthor Manuscript Author Manuscript Author ManuscriptThis is the first report of selenophene-core compounds as ER ligands. In transcription assays, several selenophenes profiling as superagonists for ERα; moreover, a few selenophenes exhibited antiproliferative activity comparable to that of 4OHT in breast cancer MCF-7 cells while being nontoxic to normal VERO cells. These new ligands could act as models for the development of novel agents leading to improved therapeutics that target the estrogen receptor.

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Regioselective Functionalization of the Imidazole Ring via Transition Metal‐Catalyzed CN and CC Bond Forming Reactions

2010

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Functionalized imidazole derivatives include compounds that are known to possess a broad range of significant biological properties or are important templates in medicinal chemistry. In the light of the importance of these heteroaromatic compounds a great deal of attention has been given to their synthesis and, in the past years, a number of methods has been described in the literature allowing for the construction of the heteroaromatic core of these substances by cyclization protocols. However, in recent years, much more attention has been focused on the design and development of efficient protocols that are based on the selective functionalization of the imidazole ring at the N-1, C-2, C-4 or C-5 position via transition metal-catalyzed reactions and enable the synthesis of imidazole derivatives, including bioactive and/or naturally occurring compounds, which cannot be accessed by other means. This critical review with 439 references covers developments in this hot area of research up to July 2009 and includes a description of synthetically important, regioselective transition metal-catalyzed IntroductionSubstituted imidazoles are important heteroaromatic compounds that are known to exhibit a broad range of biological activities such as antifungal properties, [1] analgesic activity, [2,3] anti-inflammatory activity inhibiting the p38 MAP kinase or cytokine release, [4,5] antiallergic activity, [6] antileishmanial activity, [7] and VEGF receptor I and II [I8] and neuropeptide Y antagonistic activities.[9] They are also important building blocks found in naturally occurring compounds [10] and versatile precursors to N-heterocyclic carbenes useful as ligands in various catalytically active transition metal complexes [11] and in organocatalysis. [12] Moreover, imidazolium salts can be used as environmentally friendly ionic solvents.[13] As a result, a number of methodologies for the preparation of variously substituted imidazoles has been intensively developed. [14] Methods for imidazole core synthesis include cyclocondensation reactions of a-hydroxy ketones, aamino ketones with formamide (Bredereck synthesis), [15] the base-promoted reaction of tosylmethyl isocyanide (TosMIC) and its substituted derivatives with aldimines, polymer-bound imines or imidoyl chlorides (van Leusen reaction), [16] reaction of amidines with ahalo ketones, [17] reaction of a-diketones with ammoAdv. Synth. Catal. 2010, 352, 1223 -1276 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1223 REVIEW nia and aldehydes (Debus-Radziszewski reaction), [18] condensation of a-hydroxy ketones with aldehydes and AcONH 4 in the presence of diacetoxyiodobenzene, [19] reaction of a-(hydroxyimino) ketones with 1,3,5-trisubstituted hexahydro-1,3,5-triazines, [20] cyclization reaction of a-halo ketones and N-acetylguanidine, [21] treatment of the sodium enolate salts of Nacyl-C-formylglycine esters with acid and KSCN, [22] pyrolysis of a-azido ketones, [23] condensation of aamino ketals with imidates followd by cyclization in refluxing 4 M HCl/dioxane...

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Sterics versus Electronics: Regioselective Cross‐Coupling of Polybrominated Thiophenes

Cited by 24 publications

References 21 publications

Thiophene‐Extended Nickel Thiazoledithiolene: π‐Extended Fused‐Ring Metal Dithiolenes with Stabilized Frontier Orbitals

Thiophene‐Extended Nickel Thiazoledithiolene: π‐Extended Fused‐Ring Metal Dithiolenes with Stabilized Frontier Orbitals

Selenophenes: Introducing a New Element into the Core of Non‐Steroidal Estrogen Receptor Ligands

Regioselective Functionalization of the Imidazole Ring via Transition Metal‐Catalyzed CN and CC Bond Forming Reactions

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