Esther Domínguez

A Nonsymmetric Pincer-Catalyzed Suzuki-Miyaura Arylation of Benzyl Halides and Other Nonactivated Unusual Coupling Partners

The catalytic activity of a PCN-type palladium pincer complex is evaluated in the construction of C(sp(2))-C(sp(2)) and C(sp(2))-C(sp(3)) bonds by Suzuki-Miyaura cross-couplings employing nontypical substrates such as benzyl halides, alpha-haloenones, or alkylboronic acids as coupling partners. Most of the reported reactions are achieved in aqueous media, with all of the advantages implied.

A general and efficient PIFA mediated synthesis of heterocycle-fused quinolinone derivatives

Abstract A new application of the hypervalent iodine reagent phenyliodine(III)bis(trifluoroacetate) (PIFA) has been developed for the construction of a series of N, O, S-containing heterocycle-fused quinolinone derivatives in a general and efficient way. An alternative approach to the formation of these novel tricyclic heterocycles by a PIFA mediated aryl–heteroaryl coupling reaction is also presented.

Novel applications of hypervalent iodine: PIFA mediated synthesis of benzo[c]phenanthiridines and benzo[c]phenanthridinones

A short and efficient access to benzo[c]phenanthridines and phenanthridinones is achieved by the action of phenyliodine(III)-bis(trifluoroacetate) (PIFA) on properly substituted benzylnaphthylamines and naphthylbenzamides, respectively. This reagent promotes a non-phenolic oxidative biaryl coupling process, the key step of the synthesis. A study of the electronic and steric requirements of the substrates is carried out since, in some cases, dimerization processes prevail over intramolecular cyclization. A mechanistic proposal is also included.

Palladium NCN and CNC pincer complexes as exceptionally active catalysts for aerobic oxidation in sustainable media

The oxidation of secondary benzyl alcohols is catalyzed by two palladacycles at atmospheric pressure in PEG-400, a sustainable reaction media. Recycling of the active catalytic species is performed up to the 5th run, and catalyst loadings decreased down to 10−8 mol%, thus achieving unprecedented TON and TOF values. In addition, the same conditions proved to be effective for the aerobic oxidation of benzyl methylene compounds, a scarcely explored process by palladium catalysts.

Toward Safer Processes for C—C Biaryl Bond Construction: Catalytic Direct C-H Arylation and Tin-Free Radical Coupling in the Synthesis of Pyrazolophenanthridines

A series of pyrazolo[1,5-f]phenanthridine derivatives has been efficiently synthesized by a short, straightforward sequence. A tandem amine-exchange/heterocyclization of enaminones was successfully applied to the regioselective preparation of 1,5-diarylpyrazole intermediates with structure resemblance to relevant nonsteroidal anti-inflammatory drugs such as celecoxib or tepoxalin. The final key step, cyclization by intramolecular biaryl bond formation, was accomplished by two alternative methodologies: radical coupling and catalytic direct arylation via C-H activation. The scope and limitations of the two methodologies have been explored and their complementariness has been established. In addition, polymer-supported heterogeneous catalysts have been compared with homogeneous analogues. In the radical process, toxic tin derivatives have been avoided in order to employ environmentally safer protocols.

Towards the rehabilitation of the Leuckart reductive amination reaction using microwave technology

Abstract Leuckart reductive amination of carbonyl compounds was dramatically enhanced with respect to conventional heating by a specific microwave effect when the reaction was performed, under solvent-free conditions, in a monomode microwave reactor. Excellent isolated yields (up to 97%) were attained within short reaction times (typically, 30 minutes)

Synthesis, Structure, and Catalytic Applications for ortho- and meta-Carboranyl Based NBN Pincer-Pd Complexes

o- and m-Carborane-based NBN pincer palladium complexes (oCB-L1)Pd, (oCB-L2)Pd, and (mCB-L1)Pd are synthesized in two steps from commercially available starting materials. The pincer complexes were prepared by the reaction of bis-[R(hydroxy)methyl]-1,2-dicarba-closo-dodecaborane (R = 2-pyridyl oCB-L1, 6-methyl-2-pyridyl oCB-L2) or bis-[2-pyridyl (hydroxy)methyl]-1,2-dicarba-meta-dodecaborane (mCB-L1) with [PdCl2(MeCN)2] under mild conditions. The X-ray structure determination of all carboranyl pincer complexes shows unambiguously B-H activation of the carborane cages. The results agree with the Pd-B bonds in all complexes exhibiting strong σ-electron donation. Theoretical calculations reveal the importance of considering the solid state intermolecular hydrogen bonding when investigating the trans influence in organometallic chemistry. A localized orbitals approach has also been applied to analyze the metal oxidation state in the carboranyl pincer complexes. Catalytic applications of (oCB-L1)Pd and (mCB-L1)Pd have shown the complexes are good catalyst precursors in Suzuki coupling in water and with very low amounts of catalyst loadings.

A convenient alternative route to β-aminoketones

Abstract Enaminones has been prepared and submitted to conjugate reduction with LAH and the system Al2O3/R2NH to give β-aminoketones. The latter tandem amination system has also been applied in the Mannich reaction, improving the synthesis of several new diaryl β-aminoketones. Besides, the sequential use of DMFDMA and LAH-CuI on deoxybenzoins furnishes a new route for the synthesis of enones.

A Simple Route to New Phenanthro- and Phenanthroid-Fused Thiazoles by a PIFA-Mediated (Hetero)biaryl Coupling Reaction

An application of the PIFA-mediated [PIFA: phenyliodine(III) bis(trifluoroacetate)] biaryl coupling reaction is presented and extended to the formation of heterobiaryl connections. A preliminary study of the scope and limitations of this procedure was carried out in the synthesis of phenanthroids 11 from a series of phenethyl-substituted heterocycles 10. It was observed that in some cases a competitive dimerization process took place. It was also found that the coupling step could be efficiently extended to a larger number of examples if an aromatic ring were situated fused to the 1,2-diarylethane skeleton, as in 23 and 30. The synthesis of a series of 4,5-diarylthiazoles 23a−g was therefore carried out to explore the electronic requirements and the regioselectivity of the PIFA-mediated non-phenolic coupling reaction. When the same procedure was applied to aryl-heteroarylthiazoles 30, a series of phenanthroid-fused thiazoles 31 was obtained in good overall yields. To the best of our knowledge, no oxidative aryl-heteroaryl coupling reaction of this type had previously been reported. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

An efficient copper-catalytic system for performing intramolecular O-arylation reactions in aqueous media. New synthesis of xanthones

A safe, efficient protocol for the copper-catalysed intramolecular O-arylation of 2-halobenzophenones on water to afford the valuable xanthone framework is reported. The recovery and the successful reutilization of the aqueous solution containing the copper catalyst are also presented. Moreover, the scalability and the easy setup and purification tasks of this sustainable method make it appealing for bulk industry applications.