The role of palladium catalyst and base in stereoselective transformations of (E)-2-chlorovinylsulfides

Stereoselective transformations of 2-chlorovinylsulfides in the presence of soluble (t-BuOK) or insoluble (solid KOH or Cs₂CO₃/18-crown-6) base and palladium catalyst (dppb)Pd(OAc)₂ have been studied. Depending on the substrate or catalytic system, the reaction leads to the formation of (E)-1,2-bis[aryl(or arylmethyl)thio]ethenes and/or (E)-1,4-bis[aryl(or arylmethyl)thio]-1-buten-3-ynes in yields of up to 93%.     

Adsorption from binary solvent mixtures onto silica gel by HPLC frontal analysis

Summary The chromatographic technique of frontal analysis is applied to measuring adsorption from binary liquid mixtures by silica gel. The complete adsorption isotherm of a solvent mixture is obtained by measuring the break-through curves for a series of small concentration steps of the mobile phase. This method offers a direct way to determine the composition of the stationary phase in liquid-solid chromatography with mixed mobile phases. The surface excess isotherms of all binary systems formed by benzene, cyclohexane, and 1,2-dichloroethane, at the solution-silica gel interface at 25 °C are presented. The data of the three systems are shown to be thermodynamically mutually consistent.     

New activated bisfluoroaromatic compounds

Bis (p-fluorophenylethynyl) derivatives were obtained by the reaction of bisbromoaromatic compounds withp-fluorophenylacetylene in the presence of a Pd catalyst. Subsequent oxidation of these products using an I₂-DMSO system led to new bis(p-fluorophenylglyoxaly)ketones, α-diketones, and heterocyclic compounds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 810–812, April, 1997.     

Tandem reactions of α-diazo ketones with macrocyclic olefins: diastereoselective synthesis of oxanorbornane fused macrocyclic lactones

Tandem cyclization-cycloaddition reactions of α-diazo ketones with macrocyclic olefins in the presence of rhodium(II) acetate catalyst led to the oxanorbornane fused macrocyclic di- or tetralactone ring systems in moderate yield. This forms the first example of 1,3-dipolar cycloaddition reactions with a macrocyclic olefin as a dipolarophile, affording a variety of new oxanorbornane fused macrocycles with diastereoselectivity.     

Ionic liquid–modified cellulosic hydrogels for loading and sustained release of selenourea: an ensuing inhibition of tyrosinase activity

Cellulose-based hydrogel materials were prepared and modified with tannic acid and l-methionine using ionic liquid as the solvent. The gels were prepared to develop a sustained release medium for selenourea (SeU). The drug delivery characteristics of selenourea-loaded cellulose (CSeU), selenourea-loaded tannic acid-modified cellulose (CTSeU), and selenourea-loaded L-methionine-modified cellulose (CMSeU) were investigated in aqueous media and simulated gastric fluid (SGF) media. This modified gel beads have been characterized using field emission scanning electron microscope, X-ray energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, thermogravimetry–differential thermal analysis and swelling properties and compared with those of the unmodified ones. We also investigated the inhibitory effects of SeU released from these gels on the activity of mushroom tyrosinase. Out of all the gel materials, CTSeU showed maximum SeU release both in water and SGF media. However, tyrosinase inhibitory action in PBS medium was comparable for all the three gel materials.     

Pd0-catalyzed coupling cyclization reaction of Aryl or 1-alkenyl halides with 1,2-allenyl ketones: scope and mechanism. An efficient assembly of 2,3,4-, 2,3,5-tri- and 2,3,4,5-tetrasubstituted furans

Described herein is the Pd(0)-catalyzed coupling cyclization reaction of 1,2-allenyl ketones with organic halides leading efficiently and conveniently to not only 2,3,4- and 2,3,5-trisubstituted furans but also 2,3,4,5-tetrasubstituted furans. Furthermore, this method showed high substituent-loading capability and tolerance of various substituents. The reactions of 1,2-allenyl ketones 1 e, 1 p, 1 q, and deuterated [D]1 c were performed for a mechanistic study, which demonstrated that instead of an enolization pathway, the reaction may proceed via the intermediacy of dienolate palladium and intramolecular nucleophilic attack on the pi-allyl palladium intermediate by the carbonyl oxygen.     

The dependence of sorbent/analyte type on observed differences in supercritical fluid extraction efficiencies employing extraction vessels of different dimensions

Summary The effect of extraction cell dimensions (i.d.: length) on supercritical fluid extraction (SFE) efficiencies of polychlorinated biphenyls (PCBs) is shown to be dependent on the type of sorbent used. For octadecylsilane (C18) sorbents, there is a significant increase in observed SFE recoveries of PCBs when the cell dimensions are made more broad (increased i.d.: length); whereas, no effect of cell geometry is observed when the common adsorbent, Florisil, is utilized. Additionally, recoveries decreased in proportion to the chlorine number, for the PCBs studied, for octadecylsilane sorbents, while no such effect was observed for Florisil. These results illustrate the magnitude of the matrix effect in SFE, which generally dominated observed recoveries, even in the simplest analyte/sorbent systems such as the one studied here.     

Ditertiary phosphine complexes of (ν-allyl)dicarbonylmolybdenum(II) and -tungsten(II)

Compounds of the type [XM(CO)₂(ν-allyl)L₂] (where X = Cl and Br; M = Mo and W; L₂ = Ph₂PCH₂PPh₂ and Ph₂ PCH₂CH₂PPh₂) have been prepard from the corersponding MeCN complexes. The spectral properties of these compounds and the effects of chelate rign size on ³¹P coordination shifts and J(¹⁸³W—³¹P) have been investigated.     

Copper‐Catalyzed Carbotrifluoromethylation of Unactivated Alkenes Driven by Trifluoromethylation of Alkyl Radicals

We report herein an unprecedented protocol for radical carbotrifluoromethylation of unactivated alkenes. With Cu(OTf)₂ as the catalyst, the reaction of unactivated alkenes, TMSCF₃ and activated alkyl chlorides at room temperature provides the corresponding carbotrifluoromethylation products in satisfactory yields. Directed by trifluoromethylation of alkyl radicals, the method exhibits an excellent regioselectivity that is opposite to those driven by CF₃ radical addition.     

Reinvestigation of the Nazarov cyclization of 1-(3-hydroxypropynyl)cyclododecan-1-ol to bicyclo[10.3.0]pentadec-1(12)-en-13-one

Reinvestigation of the acid-catalyzed cyclization of 1-(3-hydroxypropynyl)cyclododecan-1-ol under the conditions of the Nazarov reaction demonstrated that this conversion yields two isomeric bicyclic ketones, namely, bicyclo[10.3.0]pentadec-1(12)-en-13-one and bicyclo[10.3.0]pentadec-1-en-3-one. The latter compound is thermodynamically less stable. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1325–1327, July, 1997.