Synthesis of Highly Substituted γ‐Butyrolactones by a Gold‐Catalyzed Cascade Reaction of Benzyl Esters

Easily accessible benzylic esters of 3‐butynoic acids in a gold‐catalyzed cyclization/rearrangement cascade reaction provided 3‐propargyl γ‐butyrolactones with the alkene and the carbonyl group not being conjugated. Crossover experiments showed that the formation of the new C?C bond is an intermolecular process. Initially propargylic–benzylic esters were used, but alkyl‐substituted benzylic esters worked equally well. In the case of the propargylic–benzylic products, a simple treatment of the products with aluminum oxide initiated a twofold tautomerization to the allenyl‐substituted γ‐butyrolactones with conjugation of the carbonyl group, the olefin, and the allene. The synthetic sequence can be conducted stepwise or as a one‐pot cascade reaction with similar yields. Even in the presence of the gold catalyst the new allene remains intact.     

Ring conformations and intermolecular interactions in two fused dibenzoazocines

5‐Acetyl‐2‐chloro‐8,11‐dimethyl‐5,6,11,12‐tetrahydrodibenzo[b,f]azocine, C₁₉H₂₀ClNO, (I), crystallizes as a single fully ordered isomer, but 14‐acetyl‐8,11‐dimethyl‐7,8,13,14‐tetrahydrobenzo[f]naphtho[1,2‐b]azocine–14‐acetyl‐8,9‐dimethyl‐7,8,13,14‐tetrahydrobenzo[f]naphtho[1,2‐b]azocine (74/26), C₂₃H₂₃NO, (II), exhibits threefold whole‐molecule disorder involving both configurational and structural isomers. In (I) and in the predominant form of (II), the azocine rings adopt very similar conformations, forming boat‐shaped rings having approximate twofold rotational symmetry. There are no direction‐specific intermolecular interactions in the crystal structure of (I), but the molecules of (II) are weakly linked into chains by an aromatic π–π stacking interaction. The compounds were made under green conditions using an acid‐catalysed cyclization process having very high atom utilization.     

Magnetic susceptibility,transport and Mössbauer measurements in CuFeSe2

The study of the magnetic, transport and Mössbauer properties of eskebornite, CuFeSe₂, shows significant differences from that of its homologous sulfide, chalcopyrite (CuFeS₂). From room temperature down to 77 K, CuFeSe₂ is paramagnetic and metallic with a non-magnetic Mössbauer spectrum showing two equally populated sites for iron with very small quadrupole splitting. It seems clear that the electronic state of iron has evolved in going from chalcopyrite to eskebornite, in which it has a very weak magnetism.     

Evidence for the existence of two electronic states in the chalcopyrite-type alloys CuFe(S1−zSez)2

Results of Mössbauer spectroscopy for the chalcopyrite-type of alloys CuFe(S_1–z Se _z )₂ in the range of composition 0z0.45 are presented. Room temperature spectra show two contributions: one is a magnetic spectrum (six lines) with a value of the hyperfine field near to that of chalcopyrite (z=0, in which an antiferromagnetic order occurs belowT=823 K), the other having only one line. The relative area of the single-line contribution increases asz increases. Forz=0.2, we also made Mössbauer measurements as a function of temperature. The ratio of the two contributions evolves according to a Boltzmann law, in which the single line corresponds to the excited state at 81 K above the antiferromagnetic ground state.     

Continuous system with microwave irradiation to obtain alkyl benzoates

In this study, a continuous linear alcohol derivatization is developed. Reaction of alcohol group (ROH) with benzoyl chloride (BC) is carried out in an on-line system with UV detection. All reaction conditions, as flow rate (FR), ROH/BC molar ratio, wavelength, temperature, microwave (MW) irradiation and reaction coil size (internal diameter and length) were optimized. 0.5 mL min⁻¹, 2.49 [BC]/[ROH], 230 nm, 60 °C or medium power (225 W) when MW irradiation was used and a reactor coil of 159 μL (0.5 mm × 810 mm) were the optimum conditions. The on-line system with microwave irradiation was more efficient than the one with a water bath heating. The developed system reduces analysis time consumption, reagent amounts and this system was used to evaluate the composition of commercial samples of alcohols polyethoxylated (surfactants).     

Bayesian beta regression with Bayesianbetareg R-package

In this paper we summarize the main points of beta regression models under Bayesian perspective, including a presentation of the Bayesianbetareg R-package, used to fit the beta regression models under a Bayesian approach. Finally, beta regression models are fitted to a reading score database using, respectively, the Bayesianbetareg and betareg R-packages for Bayesian and classic perspectives.     

From Ynamides to Highly Substituted Benzo[b]furans: Gold(I)‐Catalyzed 5‐endo‐dig‐Cyclization/Rearrangement of Alkylic Oxonium Intermediates

A series of arylynamides with alkyloxy groups at the ortho position of the aryl group was prepared through a short alkylation/cross‐coupling/amidation sequence. The gold‐catalyzed conversion of these substrates combined both C? O and C? C formation steps, thus providing benzofurans with amine functionalities at the 2‐position and alkyl groups at the 3‐position. Cross‐over experiments showed that the alkyl‐migration step was an intermolecular process. X‐ray crystal‐structure analysis of two of the products supported our structural assignment. In some cases, the corresponding benzofurans without the alkyl group at the 3‐position were obtained as side‐products, which were formed through a competing protodeauration process.     

Electric field gradient sign determination in low magnetic fields perpendicular to the gamma rays in57Fe Mössbauer spectroscopy

The determination, by Mössbauer⁵⁷Fe spectroscopy, of the sign and the asymmetry parameter of the electric field gradient (EFG), in a non-magnetic powder sample, needs the use of an external magnetic field. Usually a “parallel-magnetic-field-to-the-gamma-rays” configuration is employed. In the present work, theoretically generated spectra in both configurations, parallel an perpendicular, are compared. The result is that the spectra in the perpendicular configuration show always a larger asymmetry for the same fields intensitics. In consequence, the sign determination of the EFG, is possible with magnetic fields significantly smaller in the perpendicular case than in the parallel one. Furthermore, the practical consequences are important, because EFG studies with conventional electromagnets, allowing only fields lower than 25 kGauss are feasible. As an example. Mössbauer experimental results obtained at room temperature for natural pyrite (FeS₂) in perpendicular fields of 15 and 20 kGauss, created by a conventional electromagnet, are shown here.     

A discrete-time chaos synchronization system for electronic locking devices

This paper presents a novel electronic locking key based on discrete-time chaos synchronization. Two Chen chaos generators are synchronized using the Model-Matching Approach, from non-linear control theory, in order to perform the encryption/decryption of the signal to be transmitted. A model/transmitter system is designed, generating a key of chaotic pulses in discrete-time. A plant/receiver system uses the above mentioned key to unlock the mechanism. Two alternative schemes to transmit the private chaotic key are proposed. The first one utilizes two transmission channels. One channel is used to encrypt the chaotic key and the other is used to achieve output synchronization. The second alternative uses only one transmission channel for obtaining synchronization and encryption of the chaotic key. In both cases, the private chaotic key is encrypted again with chaos to solve secure communication-related problems. The results obtained via simulations contribute to enhance the electronic locking devices.