Carbon-based Nucleophiles Research Articles

Syntheses of Isochromenes and Naphthalenes by Electrophilic Cyclization of Acetylenic Arenecarboxaldehydes

Highly substituted 1H-isochromenes, isobenzofurans, and pyranopyridines can be prepared by allowing o-(1-alkynyl)arenecarboxaldehydes and ketones to react with I2, ICl, NIS, Br2, NBS, p-O2NC6H4SCl, or PhSeBr and various alcohols or carbon-based nucleophiles at room temperature. Naphthyl ketones and iodides are also readily prepared by the reaction of 2-(1-alkynyl)arenecarboxaldehydes with I2 and simple olefins or alkynes.

Tandem Carbocupration/Oxygenation of Terminal Alkynes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Electrophilic Cyclization of 2-(1-Alkynyl)-2-alken-1-ones Using the I2/K3PO4 System: An Efficient Synthesis of Highly Substituted Iodofurans

[reaction: see text] The electrophilic cyclization of 2-(1-alkynyl)-2-alken-1-ones in the presence of various alcohols or carbon-based nucleophiles offers an efficient and straightforward route to highly substituted iodofurans under extremely mild reaction conditions. The iodo derivatives are potential synthetic intermediates for amplification of molecular complexity.

Probing the mechanism of Prins cyclisations and application to the synthesis of 4-hydroxytetrahydropyrans

Trapping intermediates on the Prins cyclisation pathway with carbon-based nucleophiles has given further insight into factors affecting the acid-mediated reactions of homoallylic alcohols with aldehydes, enabling the design of efficient syntheses of 4-hydroxy-2,6-disubstituted tetrahydropyrans.

λ 3-Iodane-mediated arenol dearomatization. Synthesis of five-membered ring-containing analogues of the aquayamycin ABC tricyclic unit and novel access to the apoptosis inducer menadione

The λ 3-iodane [bis(trifluoroacetoxy)]iodobenzene (BTI)-mediated oxidative dearomatization of 2-alkoxyarenols with soft external carbon-based nucleophiles constitutes a rapid access to highly functionalized naphthoid cyclohexa-2,4-dienones. These synthons can serve as valuable intermediates in the construction of the angularly-oxygenated benz[ a]naphthalene ABC ring system of aquayamycin- and SS-228Y-type antibiotic angucyclinones, and analogues thereof. This methodology led to the elaboration of five-membered A ring-containing analogues of this ABC tricyclic unit. In addition, the BTI-mediated oxidative activation of 2-methylnaphthol can be exploited to prepare menadione (i.e. vitamin K 3), known to induce apoptosis and autoschizis, a novel type of cancer cell death.

Synthesis of Novel Bi-, Tri-, and Tetracyclic Nucleosides by Reaction of a Common Cyclic Enamine Derived from TSAO-T with Nucleophiles

We report here the efficient regio- and stereoselective synthesis of new polycyclic nucleosides using a common cyclic enamine (7) as the starting material. In fact, the reaction of 7, easily prepared by reaction of 5'-O-Tosyl TSAO-T under basic nonnucleophilic conditions (potassium carbonate), with different classes of nucleophiles, for example, nitrogen-, oxygen-, sulfur-, and carbon-based nucleophiles, or with amino acids afforded, with total regio- and stereoselectivity, new bi-, tri-, and tetracyclic nucleosides. This straighforward route represents an original and unambiguously regio- and stereoselective pathway to these compounds. Some of these polycyclic nucleosides may be useful intermediates for a second series of reactions that may lead to the generation of structurally new nucleosides.

Efficient Syntheses of Heterocycles and Carbocycles by Electrophilic Cyclization of Acetylenic Aldehydes and Ketones.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Preparation and Catalytic Applications of Partially Fluorinated Binaphthol Ligands.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Studies toward the synthesis of angularly-oxygenated angucyclines antibiotics

The [bis(trifluoroacetoxy)]iodobenzene-mediated oxidative dearomatization of 2-alkoxyarenols, followed in situ by trapping of the resulting arenoxenium ions by soft external carbon-based nucleophiles, constitutes a rapid access to highly functionalized naphthoid cyclohexa-2,4dienones. These synthons can serve as valuable intermediates in the construction of the angularly-oxygenated benz[a]anthraquinone ABCD tetracyclic ring system of aquayamycin-like angucyclinones. This methodology so far has led to the elaboration of five-membered ring analogues of the ABC tricyclic unit of these natural products.

Efficient syntheses of heterocycles and carbocycles by electrophilic cyclization of acetylenic aldehydes and ketones.

Highly substituted oxygen heterocycles can be prepared in good yields at room temperature by reacting o-(1-alkynyl)-substituted arene carbonyl compounds with NBS, I(2), ICl, p-O(2)NC(6)H(4)SCl, or PhSeBr and various alcohols or carbon-based nucleophiles. Naphthyl ketones and iodides are readily prepared by the reaction of 2-(1-alkynyl)arene-carboxaldehydes with I(2) and simple olefins or alkynes.

Preparation and catalytic applications of partially fluorinated binaphthol ligands

New partially fluorinated binaphthols were obtained using a copper-catalyzed oxidative coupling. The corresponding enantiomerically pure compounds were prepared by fractional crystallization of the corresponding bis(menthyl)carbamates. Nucleophilic aromatic substitution using oxygen- and carbon-based nucleophiles resulted in functionalized derivatives without concomitant racemization. The titanium(IV) complexes of these ligands are catalytically active in the asymmetric oxidation of sulfides.

Cyclization of Carbonyl Groups onto Alkynes upon Reaction with IPy2BF4 and Their Trapping with Nucleophiles: A Versatile Trigger for Assembling Oxygen Heterocycles.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Cyclization of carbonyl groups onto alkynes upon reaction with IPy2BF4 and their trapping with nucleophiles: a versatile trigger for assembling oxygen heterocycles.

Iodonium ions liberated from bis(pyridine)iodonium(I) tetrafluoroborate react with ortho-alkynyl-substituted carbonyl compounds and different nucleophiles to give valuable iodinated heterocycles at room temperature, through a new and metal-free reaction sequence. Interestingly, the nature of the nucleophile can be widely modified, and not only alcohols but also several carbon-based nucleophiles can be nicely used.

Oxidized Arenol Intermediates in Intermolecular Carbon−Carbon Bond Formation. Naphthoid Cyclohexa-2,4-dienones via Oxidative Nucleophilic Substitution

Dearomatization of arenes is a powerful strategy for the preparation of functionalized cyclic olefins. Phenol oxidation can be exploited as a dearomatization tactic to produce cyclohexa-2,4-dienones. Iodine(III)-mediated oxidation of 2-alkyl- and 2-alkoxynaphthols was accomplished in the presence of an allylsilane or a silyl enol ether carbon-based nucleophile to furnish cyclohexa-2,4-dienone derivatives in moderate to good yields. This intermolecular carbon−carbon bond-forming reaction is particularly promising for the preparation of synthetically valuable naphthoid orthoquinols.

Functionalizing Heterocycles by Electron-Deficient Bonding to a Triosmium Cluster

A new synthetic methodology for adding carbon-based nucleophiles to the carbocyclic ring of quinolines has been developed, based on the electron-deficient bonding of the C(8) carbon and the protective coordination of the nitrogen atom to the metal core in the complexes Os3(CO)9(μ3-η2-C9H5(R)N)(μ-H), 1a−1h. These compounds react with a wide range of carbanions (e.g., R‘Li) to give the nucleophilic addition products Os3(CO)9(μ3-η3-C9H7(5-R‘)N)(μ-H), 2a−2l, and Os3(CO)9(μ3-η3-C9H6(3-, 4-, or 6-R)(5-R‘)N)(μ-H), 3b−3g, after quenching with trifluoroacetic acid, in isolated yields of 25−86%. In the 6-substituted derivatives, this addition is stereoselective, forming only the cis-diastereomer. In the case the 6-chloro derivative, a second product is obtained, Os3(CO)9(μ3-η2-C9H5(6-Cl)(5-C(CH3)2CN)N)(μ-H)2, 4, the result of protonation at the metal core and rearrangement of the carbocyclic ring. The trans-diastereomer of the 6-substituted derivatives can be obtained by quenching the intermediate anion of the unsubstituted complex with (CH3O)2SO2 or acetic anhydride. Nucleophilic addition to the 5-chloro complex occurs across the 3,4-bond to give Os3(CO)9(μ3-η2-C9H6(5-Cl)(4-C(CH3)2CN)N)(μ-H), 5. The addition products, types 2 and 3, can be rearomatized by reaction with diazobicyclononane (DBU)/dichlorodicyanoquinone (DDQ) or by reaction of the intermediate anion with trityl cation or DDQ. The resulting rearomatized complexes can be cleanly cleaved from the cluster by heating in acetonitrile under a CO atmosphere, yielding the functionalized quinoline and Os3(CO)12 as the only two products. Solid structures of cis-3e, trans-3e, 4, and 5 are reported.

Regioselectivity in the nucleophilic functionalization of dibenzofuran, dibenzothiophene and xanthene complexes of Mn(CO) 3+

The cationic complexes[(η 6-DBF)Mn(CO) 3]BF 4, [(η 6-DBT)Mn(CO) 3]BF 4 and[(η 6-XAN)Mn(CO) 3]PF 6 (DBF = dibenzofuran, DBT = dibenzothiophene, XAN = xanthene) are prepared. These species react with carbon-based nucleophiles to form exo-substituted cyclohexadienyl complexes. Addition is found exclusively at carbons 1 and 4. The C(1)-functionalized regioisomer predominates, especially for the DBF and XAN complexes, for which 90 to > 95% selectivity is found with stabilized nucleophiles. Preference for C(1) is greatly reduced for unstabilized magnesium and lithium nucleophiles. The origin of this selectivity is discussed. Loss of the aromatic ring from the cationic complexes in the presence of CH 3CN is found to be extremely facile for the DBF and DBT complexes owing to increased ease of ring slippage. Second-order rate constants for the displacement reactions with CH 3CN are4.6 ± 0.6 × 10 −5M −1,s −1 (DBF complex, 25°C),4.4 ± 1.0 × 10 −5,M −1,s −1 (DBT complex, 25°C) and about 1.0 × 10 −5,M −1,s −1 (XAN complex, 60°C). A crystal structure is presented for the hydride adduct of the DBF complex,[(η 5-C 12H 9O)Mn(CO) 3]: space group P2 1/c, a = 15.301(2), b = 6.4422(12), c = 12.988(2)A˚, β = 90.888(13)°, V = 1280.1(3)A˚ 3, Z = 4, D calc = 1.599Mg m −3, R = 0.0410 and wR2 = 0.0945 on 2446 reflections with F 2 > 4.0 σ(F 2).

Regiocontrol in nucleophilic ring opening of chiral epoxides of chemoenzymatic origin

Homochiral cis epoxides derived from enzymatically asymmetrized tris(hydroxymethyl)methane equivalents (THYM *) are regioselectively opened by carbon based-nucleophiles (alkyl groups or cyanides) and halides in the presence of Lewis acids. Enantio- and diastereodivergent synthesis of branched triols is reported.