Stereoselective addition of dimethyl thiophosphite to imines

Dimethyl thiophosphite (DMTP) was synthesized from dimethyl phosphite, and the diastereoselective addition of DMTP to benzaldimines bearing chiral auxiliary groups was examined. Yields of the product alpha-aminophosphonothionates ranged from 17% to 75% after chromatography. The addition of DMTP to the benzaldimine derived from (S)-phenylglycinol afforded the highest diastereoselectivity (83:17), whereas addition of DMTP to the benzaldimine derived from threonine methyl ester and alanine methyl ester were far less diastereoselective, affording 38:62 and 61:39 ratios, respectively. Addition of DMTP to the benzaldimine derived from (R)-alpha-methylbenzylamine (78:22) and (S)-serine methyl ester (73:27) were intermediate in selectivity. DMTP addition to the imines formed between serine methyl ester and acetaldehyde and isobutyraldehyde gave 55:45 and 70:30 ratios, respectively, with the diastereoselectivity corresponding roughly to the size of the alpha-alkyl group. The stereochemistry of the newly formed alpha-stereocenters resulting from the addition of DMTP to (S)- and (R)-phenylglycinol benzaldimines was confirmed by conversion of the product alpha-aminophosphonothionates to the known enantiomers of phosphonophenylglycine.     

Three-dimensional synchronous fluorescence spectrometry for the analysis of three-component alkaloid mixtures

A study of a simple and sensitive method for the determination of berberine, luguine and sanguinarine in mixtures by normal and synchronous derivative spectrofluorimetry is described. The influence of solvents and other experimental variables is discussed. A three-dimensional plot of both emission-excitation and synchronous spectra obtained by a new software program provides additional information for optimizing instrumental parameters. Linear, normal and derivative calibration graphs are established in the ng/ml range. A statistical analysis of the results and their application to synthetic and natural samples is given.     

A new polymorph of bis[2,6‐bis(1H‐benzimidazol‐2‐yl‐κN3)pyridinido‐κN]zinc(II)

The title compound, [Zn(C₁₉H₁₂N₅)₂], crystallizes in the tetragonal space group P4₃2₁2, with the monomer residing on a twofold axis. The imidazole N‐bound H atoms are disordered over the two positions, with refined occupancies of 0.59 (3) and 0.41 (3). The strong similarities to, and slight differences from, a reported P4₂2₁2 polymorph which has a 50% smaller unit‐cell volume [Harvey, Baggio, Muñoz & Baggio (2003). Acta Cryst. C 59 , m283–m285], to which the present structure bears a group–subgroup relationship, are discussed.     

Eco-friendly reductive acetamidation of arylnitro compounds by thioacetate anion through in situ catalytic regeneration: application in the synthesis of Acetaminophen™

A novel one-step reductive acetamidation of arylnitro compounds mediated by thioacetate anion in thioacetic acid via in situ catalytic regeneration was developed and applied to an efficient synthesis of Acetaminophen™.     

A monoclinic form of dendocarbin A: a borderline case of one‐dimensional isostructural polymorphism

The title compound, dendocarbin A [systematic name: (1R,5aS,9aS,9bR)‐1‐hydroxy‐6,6,9a‐trimethyldodecahydronaphtho[1,2‐c]furan‐3‐one], C₁₅H₂₂O₃, is a sesquiterpene lactone isolated from Drimys winteri var chilensis. The monoclinic phase described herein displays an identical molecular structure to the orthorhombic phase that we reported previously [Paz Robles et al. (2014). Acta Cryst. C 70 , 1007–1010], while varying significantly in chain pitch, and can thus be considered as a borderline case of one‐dimensional isostructural polymorphism.     

Surface-enhanced Raman scattering at the silver electrode/ionic liquid (BMIPF6) interface

This is the first report of in situ SER spectra of chemical species adsorbed on a Ag/room temperature ionic liquid (RTIL) interface. We have investigated the dependence of the SERS intensity of the RTIL derived from 1-n-butyl-3-methylimidazolium hexafluorophosfate (BMIPF6) adsorbed on a silver electrode. It has been shown that the BMI+ adsorbs on the silver electrode for potentials more negative than -0.4 V vs a Pt quasireference electrode (PQRE). In the -0.4 to -1.0 V potential range the SER spectra are similar to the Raman spectrum of the RTIL BMIPF6. At potentials more negative than -1.0 V some imidazolium ring vibrational modes and N-CH3 vibrations are enhanced, suggesting that the imidazolium ring is parallel to the surface and for potentials <-2.8 V the BMI+ is reduced to the BMI carbene. The potential dependence of the SERS intensities of Py adsorbed on a silver electrode in BMIPF6 has also been investigated. The results have shown that at potentials less negative than -0.8 V (vs PQRE) Py adsorbs at an end-on configuration forming an Ag-N bond. In the -0.9 to -1.4 V potential range Py molecules lie flat on the electrode surface and at potentials <-1.4 V Py is replaced by the BMI+. The electrochemical and SERS results have shown that Py has the effect of changing the oxidation of silver in that medium as well as the reduction of BMI+ to the BMI carbene. In the presence of Py the BMI+ reduction is observed at potentials near -2.4 V. The Ag electrode has presented SERS activity from 0.0 to -3.0 V.     

Nitrogen ylide-mediated cyclopropanation of lactams and lactones

Cyclopropanation of α,β-unsaturated δ-lactams and δ-lactones mediated by nitrogen ylides is described. The process tolerates different alkyl halides and gives efficiently bicyclo[4.1.0]heptanes in a totally stereoselective manner. On the other hand, ε-lactams under our experimental conditions suffer a novel process involving a skeletal reorganization to give a bicyclic[3.3.0] system.     

Franck-Condon Factors and R-Centroids for ScF,YF, and LaF Including Rotation-Vibration Effect

We have calculated Franck-Condon factors and R-centroids for several singlet systems of ScF, YF, and LaF, taking into account the effect of rotation-vibration interaction. It has been found that this effect is far from being negligible for several cases.     

Calcium-induced aggregation of bovine caseins: effect of phosphate and citrate

The formation of colloidal particles by Ca²⁺ precipitation of whole caseinates in the presence of phosphate (Pi), citrate (Cit), or both of the anions in concentrations found to be effective in previous works was followed comparing the colloidal particle size and the ionic and proteic composition of the precipitates obtained. Ca²⁺ was incorporated to the precipitate and colloidal particles in a different way than Pi, differences which were related to the presence of Pi and/or Cit in the media. A sequential salting-out process due to progressive Ca²⁺ binding to at least two kinds of sites was observed. The precipitation curves were fitted, and the affinity constants and binding site numbers were calculated with a modification of the Farrell’s equation based on the concept of Wyman’s linked functions. Precipitates obtained at low total Ca²⁺ concentrations in different conditions varied their casein composition. Colloidal particles appeared at the beginning of the second salting-out step, in different amount, and in average size according to the presence or absence of Pi and/or Cit in the media. Consideration of these differences showed that Cit favored the formation of bigger colloidal particles, acting especially in the first steps of the casein aggregation and conditioning the mechanism of this process.