Gregorio Asensio

Silver-Catalyzed C-C Bond Formation Between Methane and Ethyl Diazoacetate in Supercritical CO2

Supercritical carbon dioxide solvent facilitates transformation of the generally inert carbon-hydrogen bonds in methane. Even in the context of hydrocarbons’ general resistance to selective functionalization, methane’s volatility and strong bonds pose a particular challenge. We report here that silver complexes bearing perfluorinated indazolylborate ligands catalyze the reaction of methane (CH4) with ethyl diazoacetate (N2CHCO2Et) to yield ethyl propionate (CH3CH2CO2Et). The use of supercritical carbon dioxide (scCO2) as the solvent is key to the reaction’s success. Although the catalyst is only sparingly soluble in CH4/CO2 mixtures, optimized conditions presently result in a 19% yield of ethyl propionate (based on starting quantity of the diazoester) at 40°C over 14 hours.

Gold(I)-catalyzed intermolecular oxyarylation of alkynes: unexpected regiochemistry in the alkylation of arenes.

The reaction between acetylenes and sulfoxides, studied as a test case for gold-catalyzed intermolecular addition, provides the oxyarylation compounds 3 in good yields. Unpredictably, in all cases a single regioisomer arising from the electrophilic aromatic alkylation at the position adjacent to the sulfur atom is obtained instead of the expected Friedel-Crafts regioisomer. A new concerted mechanism based on DFT calculations is proposed to account for the products in this intermolecular gold(I)-catalyzed reaction.

Competitive and Selective Csp3Br versus Csp2Br Bond Activation in Palladium‐Catalysed Suzuki Cross‐Coupling: An Experimental and Theoretical Study of the Role of Phosphine Ligands

Phosphine ligands have been demonstrated to have an effect on reactivity and selectivity in the competitive intramolecular palladium-catalysed Suzuki-Miyaura coupling of dibromo sulfoxide 1a possessing two different hybridised electrophilic carbons. It was found that the bromine bond to the sp(3)-hybridised carbon is selectively replaced in the presence of unhindered phosphines such as PPh(3) or xantphos. The use of hindered phosphine ligands such as P(o-tol)(3) and P(1-naphthyl)(3) reversed the selectivity, conducting the cross-coupling at the Csp(2)-Br. Identical trends were observed in external competition experiments carried out with bromomethyl sulfoxide and different substituted bromoarenes. DFT and DFT/MM calculations showed that the selectivity observed is mainly due to the different facility of the ligands to dissociate. Bisphosphine catalysts favour coupling at the sp(3) carbon, whereas monophosphine catalysts prefer the sp(2) carbon.

Why Is the Suzuki−Miyaura Cross-Coupling of sp3 Carbons in α-Bromo Sulfoxide Systems Fast and Stereoselective? A DFT Study on the Mechanism

The stereoselectivity-determining oxidative addition step in the Suzuki-Miyaura cross-coupling of alpha-bromo sulfoxides is analyzed computationally through DFT calculations on a model system defined by Pd(PMe(3))(2) and CH(3)SOCH(2)Br. Both monophospine and bisphosphine complexes have been considered, different reaction pathways being characterized through location of the corresponding transition states. The lowest energy transition states correspond to nucleophilic substitution mechanisms, which imply inversion of configuration at the carbon, in good agreement with experimental data on the process. The energy-lowering and stereodirecting role of the sulfinyl substituent is explained through its attractive interactions with the palladium center, which are only possible in the most favored mechanisms.

Competitive Gold‐Activation Modes in Terminal Alkynes: An Experimental and Mechanistic Study

The competition between π- and dual σ,π-gold-activation modes is revealed in the gold(I)-catalyzed heterocyclization of 1-(o-ethynylaryl)urea. A noticeable effect of various ligands in gold complexes on the choice of these activation modes is described. The cationic [Au(IPr)](+) (IPr=2,6-bis(diisopropylphenyl)imidazol-2-ylidene) complex cleanly promotes the π activation of terminal alkynes, whereas [Au(PtBu3 )](+) favors intermediate σ,π species. In this experimental and mechanistic study, which includes kinetic and cross-over experiments, several σ-gold, σ,π-gold, and other gold polynuclear reaction intermediates have been isolated and identified by NMR spectroscopy, X-ray diffraction, or MALDI spectrometry. The ligand control in the simultaneous or alternative π- and σ,π-activation modes is also supported by deuterium-labeling experiments.

NHC-stabilized gold(I) complexes: suitable catalysts for 6-exo-dig heterocyclization of 1-(o-ethynylaryl)ureas.

3-Substituted 1-(o-ethynylaryl)ureas 1 selectively undergo either 6-exo-dig or 5-endo-dig cyclization (to give 4-methylene-3,4-quinazolin-2-ones 2 or indoles 3, respectively) depending on the choice of the metal, ligand, and reaction conditions. The best results (up to 96% yield) in the preparation of the hydroamination products 2 are achieved with the highly bulky NHC-stabilized cationic gold(I) complex [Au(IPr)](+). Conversely, ureas bearing an internal alkyne lead to the 5-endo-dig cyclization mode regardless of the gold(I) complex employed. Whereas the nature of the substituent at N-3 does not have any influence on the regiochemistry observed, it does, in some cases, affect the efficiency of these transformations.

Enzyme-mediated enantioselective acylation of secondary amines in organic solvents

Abstract Porcine pancreatic lipase (PPL) and lipase Amano P catalyze the enantioselective acylation of cyclic 1,2- and 1,3-amino alcohol derivatives in organic solvents. The enatiomeric excesses (ee′s) were shown to depend on the enzyme, reaction time, temperature and type of substrate.

A new and specific method for the monomethylation of primary amines

The reduction of monomeric methyleneamines, representing a convenient and highly specific procedure for the title reaction, is studied.

Gold(I)-Catalyzed Intermolecular Cycloaddition of Allenamides with α,β-Unsaturated Hydrazones: Efficient Access to Highly Substituted Cyclobutanes

α,β-Unsaturated N,N-dialkyl hydrazones undergo a mild [2 + 2] cycloaddition to allenamides when treated with a suitable gold catalyst. The method, which represents the first application of N,N-dialkyl hydrazones in gold catalysis, is compatible with a wide variety of substituents at the alkenyl moiety of the hydrazone component, proceeds with excellent levels of regio- and diastereoselectivity, and provides densely substituted cyclobutanes with good to excellent yields.

Osmium(III) Complexes with POP Pincer Ligands: Preparation from Commercially Available OsCl3·3H2O and Their X-ray Structures

Complexes OsCl(3){dbf(P(i)Pr(2))(2)} [1; dbf(P(i)Pr(2))(2) = 4,6-bis(diisopropylphosphino)dibenzofuran], OsCl(3){xant(P(i)Pr(2))(2)} [2; xant(P(i)Pr(2))(2) = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene], and OsCl(3){xant(PPh(2))(2)} [3; xant(PPh(2))(2) = 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene] have been obtained in high yield by the reaction of the corresponding diphosphine with OsCl(3)·3H(2)O. The ruthenium(III) counterparts RuCl(3){dbf(P(i)Pr(2))(2)} (4), RuCl(3){xant(P(i)Pr(2))(2)} (5), and RuCl(3){xant(PPh(2))(2)} (6) are similarly obtained from RuCl(3)·3H(2)O in moderate yields. The X-ray structures of dbf(P(i)Pr(2))(2) and complexes 1-3 are also reported.