Ionic liquids as recyclable solvents for diethylaminosulfur trifluoride (DAST) mediated fluorination of alcohols and carbonyl compounds

The first simple and efficient method for the synthesis of mono and gem-difluorinated molecules using [C₈mim][PF₆] ionic liquid as a recyclable solvent medium with diethylaminosulfur trifluoride (DAST) as the fluorinating reagent, is reported.     

Conformational mobility and intramolecular rearrangements of bis(3-thioxo-1-phenylpropenyl) sulfide

Possible intramolecular transformations of bis(3-thioxo-1-phenylpropenyl) sulfide were studied by the quantum-chemical semiempirical AM1 method. A group of the most stable, potentially spectroscopically discernible rotamers was distinguished. A possibility of intramolecular rearrangements giving thiirane structures was considered. The ability of bis(3-thioxo-1-phenylpropenyl) sulfide for spontaneous trimerization was evaluated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2255–2261, December, 1999.     

Boron trifluoride catalysed reactions of 2,2,2-trichloroethyl 6-diazopenicillanate with aromatic aldehydes: rearrangements via penam c(5)-c(6) bond cleavage.

The BF₃·Et₂O catalysed reactions of diazopenicillanate 1 with aromatic aldehydes provide 2,3-dihydrothiazolo[2,3-b][1,3]oxazin-5-ones 4 $\text{via}$ C(5)-C(6) cleavage of 6-formyl-penicillanates 8.     

Paramagnetic palladacycles with Pd(III) centers are highly active catalysts for asymmetric aza-Claisen rearrangements

A combination of spectroscopic and electrochemical methods--XANES, EXAFS, X-ray, (1)H NMR, EPR, M?ssbauer, and cyclic voltammetry--demonstrate that the most efficient Pd catalysts for the asymmetric rearrangement of allylic trifluoroacetimidates unexpectedly possess in the activated oxidized form a Pd(III) center bound to a ferrocene core which remains unchanged (Fe(II)) during the oxidative activation. These are the first recognized Pd(III) complexes acting as enantioselective catalysts.     

Reaction of 1,2-0-Alkylidenehexofuranurono-6,3-Lactones with Diethylaminosulfur Trifluoride (DAST)

Reaction of 1,2-0-alkylidenehexofuranurono-6,3-lactones with diethylaminosulfur trifluoride (DAST) led to 1,2-0-alkylidene-5-deoxy-5-fluorohexofuranurono-6,3-lactones (13–30%) together with 1,2-0-alkylidene-3,6-anhydro-6,6-difluorohexofuranoses (45–58%). Evidence was found for participation of the hydroxyl group at C-5 in the formation of the difluorides. Trifluoro compounds could not be prepared by reaction with DAST but were formed from the difluorides by triflate formation and displacement using tetra-n-butylammonium fluoride.     

A mass spectral study of intramolecular rearrangements in cis-M(CO)4(13CO)piperidine (M = Cr,W) derivatives

Low voltage mass spectra of cis-M(CO)₄(¹³CO)piperidine (M = Cr,W) show the initial loss of CO to proceed with complete scrabling of the label between axial and equatorial sites.     

The reactions of aromatic compounds with bromine trifluoride (2): Octafluoronaphthalene

The reaction of bromine trifluoride with octafluoronaphthalene has been investigated, from which was obtained decafluoro-1,2-benzocyclohexa-1,4-diene, 2-bromo-undecafluorotetralin and a mixture of dibromotetradecafluorobicylo [4,4,0] decene isomers. Dehalogenation and reduction gave decafluoro-1,2-benzocyclohexa-1,3-diene in addition to the 1,4-diene and 2$\text{H}$-undecafluorotetralin, a similar mixture being obtained from the dibromo decene. The reactions of the dienes and bromofluorotetralin with methoxide ion have also been studied.     

Structure and bonding of vanadium(V) complexes with hydroxyurea in aqueous solution: density functional theory investigations of isomers and intramolecular rearrangements

Extensive geometry optimizations have been performed at the BP86 level of density functional theory, in order to identify the most stable isomer of pentacoordinated [VO(OH)UH2O]+ and [VOU(H2O)2]2+ as well as of hexacoordinated [VO(OH)U(H2O)2]+ and [VOU(H2O)3]2+ complexes (U = hydroxyurea anion). Most of these are conformationally very flexible, with up to 12 isomers within an energy range of 5 kcal/mol. The most stable hexacoordinate forms are characterized by the oxo ligand in trans position to the carbonyl O atom of U. Bulk solvent effects on the relative stabilities, estimated from a polarizable continuum model, are indicated to be small and do not affect the energetic sequence of the isomers significantly. Details of the coordination sphere of the most stable isomers in aqueous solution (coordination number, protonation state) have been studied with Car-Parrinello molecular dynamics simulations. The preferred mechanisms of interconversion between selected [VO(OH)U(H2O)2]+ isomers, according to the DFT computations, involve proton transfers between H2O and OH or between O and OH ligands in the coordination sphere of the metal, assisted by a water molecule from the second hydration sphere.     

Gold(I)-catalyzed intramolecular hydroamination of alkyne with trichloroacetimidates

[reaction: see text] A study on the gold (I)-catalyzed intramolecular hydroamination of trichloroacetimidates derived from propargyl and homopropargyl alcohols is described. In the presence of 2-5 mol % of cationic Au(I) complex, a variety of trichloroacetimidates undergo efficient hydroamination under an exceptionally mild condition. An orthogonality of the current catalytic protocol with those using a stoichiometric electrophile as well as a preliminary synthetic application as a stable precursor of 2-acylamino-1,3-diene has been demonstrated.     

The reactions of aromatic compounds with bromine trifluoride(I): hexafluorobenzene and its derivatives

The reactions of mixtures of bromine trifluoride and bromine with hexa-, penta- and bromopenta-fluorobenzene, with octafluorotoluene and decafluoro -p-xylene and 2,3,4,5,6-pentafluorotoluene and -anisole have been investigated. The initial products were polyfluorocyclohexa-1,4-dienes, substituent groups being in the 1-position for electron withdrawing and the 3-position for electron donating groups respectively. The dienes then reacted further to add bromine monofluoride across one or both of the diene double bonds to give bromofluorocyclohexene or polybromofluorocyclohexane isomer mixtures. In the absence of added bromine, no reaction occurred with hexafluorobenzene and reaction was less vigorous and complete with pentafluorobenzene and 2,3,4,5,6-pentafluoroanisole. The mechanism of reaction has been discussed in terms of the ionization potential of the aromatic substrates and the formation of radical cations.     

Platinum(II) molecular triangle with a deep intramolecular cavity

Depending on the conditions, the reaction of K 2PtCl 4 with 1,3-bis( N-pyrazolyl)benzene (bpzphH) yields either Pt(bpzph)Cl, [Pt(mu-bpzph)Cl] 3, or a mixture of these products. In the case of the C 3-symmetric trimer, each bpzph (-) ligand is bidentate with the metal bonded to a pyrazolyl group and to the phenyl group at the 6 position; the remaining pyrazolyl group bridges to an adjacent platinum center. The crystal structure confirms that each complex is chiral with an unusually deep (approximately 8 A) intramolecular cavity; enantiomeric pairs of trimers encapsulate the diethyl ether solvate. NMR studies establish that the trimer exhibits excellent thermal and kinetic stability. Substitution of the chloride ligands provides a strategy for elaborating the macrocycle.     

Vibrational spectra of trifluoromethylsulfur trifluoride and bis(trifluoromethyl) sulfur difluoride

Infrared spectra of the gas phase from 2000 to 400 cm⁻¹ and Raman spectra of the liquid phase from 2000 to 100 cm⁻¹ have been obtained for CF₃SF₃ and (CF₃)₂SF₂. For both compounds the assignment of the sulfur—fluorine stretching fundamentals supports equatorial perfluoroalkyl substitution on sulfur.     

Photoinduced rearrangements of 3,3'-bis(arylbenzofurans)

Complex tetracyclic ring systems were assembled by a photoinduced rearrangement of 3,3'-bis(arylbenzofurans). Irradiation of 1 under N(2) atmosphere yielded the benzonaphthofurans 2 in 75-90% yield. When the reaction was conducted under an O(2) atmosphere in the presence of tetracyanoethylene (TCNE) a different reaction pathway was observed leading to the isolation of 3 as the major product. Also, the photochemical properties of these novel structures were investigated.     

A novel hydrogenation of conjugated dienes catalyzed by halogenotris(triphenylphosphine)cobalt(I) activated with boron trifluoride etherate

CoX(PPh₃)₃ (X Cl, Br, I) exhibits a fairly high catalytic selectivity in the presence of BF₃-OEt₂ for the hydrogenation of conjugated dienes such as 1,3-butadiene, 2-methyl-1,3-butadiene, and 1,3-pentadiene at ambient temperature and pressure to give 1-butene, 3-methyl-1-butene, and 1-pentene, respectively, as the main product, where the substituted double bond is preferentially hydrogenated. The rate of hydrogenation is independent of the diene concentration and proportional to the hydrogen pressure and to the catalyst concentration. Addition of AgClO₄ instead of BF₃-OEt₂has essentially the same effect on the activity and selectivity for the hydrogenation of dienes when an analogous cobalt(I) complex, CoBr(PPh₂Me)₃, is used as the catalyst. It is proposed that the rate of hydrogenation is determined by a reaction of molecular hydrogen with a cationic tris(tertiary- phosphine) (diene)cobalt(I) species.