Orifluoroacetylation and dehydration of 20-hydroxyecdysone acetonides. Synthesis of stachisterone B

Orifluoroacetylation of the 25(OH)-group with subsequent dehydration of the 14(OH)-group takes place in the reaction of 20-hydroxyecdysone 20,22-acetonide and 2,3:20,22-diacetonide with trifluoroacetic anhydride in the presence of pyridine. Dehydration of the 14(OH)-group gives rise to stachisterone B derivatives, which are hydrolyzed to give the phytoecdysteroid stachisterone B.     

Synthesis,Characterization, and Symmetry Relations of the Crystal Structures of Some Bis(dioxane) Adducts of Group 1 / Group 13 Heterometallic Trifluoroacetates

Four bis(dioxane) adducts of mixed‐metal trifluoroacetates, M[M′(O₂CCF₃)₄(C₄H₈O₂)₂] (M = Na, K, Cs, M′ = In and M = Cs, M′ = Ga) were synthesized by reaction of alkali metal trifluoroacetate and group 13 element trifluoroacetate in 1,4‐dioxane and completely characterized including X‐ray structure determination. Geometric parameters, empirical bond valences and frequencies of the symmetric C=O stretching vibrations show that the moisture sensitive solids are composed of dimeric structural moieties with site symmetry 1 , containing alkali metal ions and bis(dioxane)tetrakis(trifluoroacetato)indate or ‐gallate ions. The dimeric units are further connected by weaker “intermolecular” dioxane interactions to neighboring alkali metal ions. Closer inspection of space group symmetry, unit cell parameters and atom sites allows to rationalize the compounds as members of two isotypic pairs that are further closely related due to the group‐subgroup relation of their monoclinc space groups to a common orthorhombic supergroup.     

Rare earth complexes with 4-methylmorpholine-N-oxide

Complexes of rare earth trifluoroacetates (TFA) with 4-methylmorpholine-N-oxide (MMNO) of composition Ln(TFA)3·3MMNO (Ln=Eu, Dy, Ho, Er, Yb and Y) were synthesized and characterized by elemental analysis data, complexometric titration with EDTA, IR absorption spectra, thermogravimetric analyses and differential scanning calorimetry (DSC) in N₂ atmosphere. Infrared spectroscopy data revealed that the MMNO molecules are bound to the central ion through the oxygen of NO groups. These data suggest that the trifluoracetate groups are also coordinated. Thermogravimetric curves indicate that the decomposition of MMNO begins at approximately 350 K and results in Ln₂O₃ residue at around 1170 K. A theoretical kinetic study was carried out using a QBASIC program with the TG input data for the Dy complex. This revised version was published online in August 2006 with corrections to the Cover Date.     

Readily hydrolysable cellulose esters as intermediates for the regioselective derivatization of cellulose; II. Soluble,highly substituted cellulose trifluoroacetates

Cellulose trifluoroacetate (CTFA) with DS values of 1.5 and 2.1 and DP values ranging from 170 to 800 have been prepared free from impurities of the reaction mixture (weakly bound trifluoroacetic acid) and of the procedure of isolation (diethyl ether). The CTFAs are soluble in DMSO, DMF, pyridine, and THF and thermostable up to 250 °C. A convenient synthetic method for CTFAs with DS 1.5 involves the acylation of cellulose with mixtures of trifluoroacetic acid (TFA) and trifluoroacetic anhydride (TFAA, 33% v/v) at room temperature for 4 h and subsequent treatment of the crude polymer at 150 °C and 80 Pa for 40 min. The preparation of CTFAs with DS-values up to 2.1 requires the addition of chloroform and 16 h reaction time.¹³ C-NMR studies as well as HPLC analyses after methylation and chain degradation show a preferred trifluoroacetylation of the primary hydroxy groups of the cellulose. The extent of depolymerization during the trifluoroacetylation was investigated for various cellulose materials. The cleavage of the trifluoroacetyl groups is possible by treating the derivative with a protic medium like water. Total hydrolysis of CTFA dissolved in DMF with water (room temperature) takes 6 min. The first paper on this topic was concerned with cellulose formates (Schnabelrauchet al., 1992).     

Gas-Liquid Chromatography of Sterol Glycosides

Abstract

GLC and mass spectrometric data for sitosterol glycoside tetratrimethylsilylether and the corresponding trifluoroacetate and heptafluorobutyrate esters are presented and discussed. The trifluoroacetate is considered the most satisfactory derivative for direct analysis by GLC and mass spectrometry.     

Indolopyridines containing a bridgehead heteroatom. 12. Synthesis and reduction of 12-arylidene-5,6-dihydroindolo[2,1-a]isoquinolinium trifluoroacetates

Condensation of 5,6-dihydroindolo[2,1-a]isoquinoline with aromatic aldehydes in trifluoroacetic acid afforded 12-arylidene-5,6-dihydroindolo[2,1-a]isoquinolinium trifluoroacetates. Hydrogenolysis of these salts on rhenium heptasulfide at elevated temperature and hydrogen pressure yielded indolo[2,1-a]isoquinolines, while reduction with sodium borohydride gave 12-arylmethylindoloisoquinolines. Photoluminescence was found for some indolo[2,1-a]isoquinolines.     

The reactivity of organothallium compounds. Kinetics and mechanism of iodination of diarylthallium salts by molecular iodine in dioxane

The kinetics and mechanism of the reactions of diarylthallium, trifluoroacetates with molecular iodine in dioxane solutions have been studied. The reaction has the overall second order with the first order with respect to each reagent. The effect of substituents in the aromatic ring on the rate constant of iodination is described by the equation logk ₂ρσ⁺(ρ=-1.60, r=0.97). The reaction is catalyzed by the iodide ion. The activation enthalpies and entropies of iodination of diarylthallium trifluoroacetates in dioxane and di(p-anisyl)thallium trifluoroacetate in various solvents have been calculated. The effect of solvents on the rate constant of iodination of di(p-anisyl)thallium trifluoroacetate has been studied. The reaction mechanism is considered as an electrophilicS _EC process. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 451–455, March, 1999.     

Facile synthesis of α,α-difluoroalkyl aryl thioethers and their oxidative desulfurization-fluorination to trifluorides

Alkyl 2-arylthio-2,2-difluoroacetates are synthesized in 52-77% yield from alkyl 2-(arylthio)acetates via two succeeding fluoro-Pummerer rearrangements using the reagents combination of N-haloimides as electrophiles and excess Py·9HF as the fluoride source at room temperature. Subsequent treatment of the formed fluorinated thioethers with the same reagents at elevated temperature gave alkyl trifluoroacetates in almost quantitative yield under optimised conditions by oxidative desulfurization-fluorination.     

Strong flux pinning enhancement in YBa2Cu3O7-x films by embedded BaZrO3 and BaTiO3 nanoparticles

YBa2Cu3O7-x (YBCO) films with embedded BaZrO3 and BaTiO3 nanoparticles were fabricated by metalorganic deposition using trifluoroacetates (TFA-MOD). Both X-ray diffraction and transmission electron microscopy revealed that these BaZrO3 and BaTiO3 nanoparticles had random orientations and were distributed stochastically in the YBCO matrix. The unique combined microstructure enhances the critical current density (Jc) of the BaZrO3/BaTiO3 doped-YBCO films, while keeping the critical transition temperature (Tc) close to that in the pure YBCO films. These results indicate that BaZrO3 and BaTiO3 nanoparticles provide strong flux pinning in YBCO films.