A new paradigm for cationic cyclization of iron tricarbonyl diene complexes with pendant alkenes and arenes

A new example of stereospecific cationic cyclization of iron tricarbonyl diene complexes with pendant alkenes and arenes is provided. Protonation of a double bond vicinal to the iron tricarbonyl diene moiety is employed to trigger the cyclization, rather than the previously reported Lewis/protic acid dehydroxylation of diastereomeric alcohols, eliminating one step of separation and avoiding some reactivity problems previously encountered for one of the alcohol diastereoisomers. [reaction: see text]     

PROPERTIES OF AN UNUSUAL PHOTOPRODUCT OF U.V. IRRADIATED THYMIDYLYL-THYMIDINE

Abstract— One of the four major photoproducts formed by UV irradiation of TpT in aqueous solution has a number of unusual properties. This compound, which we arbitrarily call TpT⁴, is produced irreversibly from TpT with single-hit kinetics and seems to represent a novel pathway for TpT photolysis different from the conventional cyclobutane ring dimer formation. This communication describes the preparative isolation of TpT⁴ by ion-exchange chromatography on DEAE-cellulose and its UV, fluorescence and IR spectra. TpT⁴ has an absorption maximum at 325 mμ, fluoresces at 405 mμ when excited at 325 mμ, and has an IR spectrum consistent with the assumption that one of the thymine rings has been converted to a pyrimidin-2-one structure. In addition, TpT⁴ appears to have both pyrimidine rings linked together and does not contain a peroxide group as previously supposed. Spectrophotometric titration shows that TpT⁴ has a pKâ of 10.75 and is unstable to prolonged treatment at extreme pH. A model structure consistent with the present data is given. This model contains the glycosidic and phosphodiester bonds intact with a 5-methylpyrimidine-2-one ring and a thymine ring joined in ether linkage at the C₄ positions, with an OH at the C₄ position in the thymine ring.     

Vibrational spectroscopy of 3,4-difluorocyclobutenes: cis-d0, trans-d0 and trans-d4 species

Infrared and Raman spectra were recorded for cis-3,4-difluorocyclobutene (cDFCB) and trans-3,4-difluorocyclobutene-d4. Unscaled density functional theory (DFT) calculations of frequencies and intensities at the B3LYP/6-311++G(d,p) level supported the complete assignment of the vibrational fundamentals. The previous assignment of fundamentals of trans-3,4-difluorocyclobutene was revised. An unusual blue shift occurs for the methylenic CH-stretching frequencies of cis-3,4-difluorocyclobutene in going from the gas phase to the liquid phase. This hydrogen bond effect is related to similar observations recently reported and interpreted. The blue shift does not occur for the vinylic CH bonds of the cis isomer and does not occur for either type of CH bond in the trans isomer.     

1,5‐Asymmetric induction during nucleophilic additions to arenetricarbonylchromium complexes: tricarbonyl(η6‐1‐methyl‐4‐{spiro[(1R,2S)‐1,7,7‐trimethylbicyclo[2.2.1]heptane‐3,2′‐1,3‐dioxolan]‐2‐yloxy}benzene)chromium

The tricarbonylchromium unit bound to the arene ring of the chiral title complex, [Cr(C₁₉H₂₆O₃)(CO)₃], is rotated by ca 25° in agreement with the proposed mechanism for 1,5‐asymmetric induction of nucleophilic attack.     

TRIUMF resonant ionization laser ion source

The range of isotopes available at the TRIUMF Isotope Separator Accelerator (ISAC) facility has been greatly enhanced by adding a Resonance Ionization Laser Ion Source (RILIS). A large wavelength range is accessible with the fundamental, second and third harmonic generation of titanium-sapphire laser light. In addition a dedicated laser is available for non-resonant laser ionization. The first on-line beam ⁶²Ga was delivered in Dec. 2004. In general RILIS improves the intensity, purity and emittance of ion beams. ⁶²Ga and ²⁶Al and Be beams have been delivered so far on-line. This work was financed by TRIUMF which is federally funded via a contribution agreement through the National Research Council of Canada.     

Simultaneous Amplification of Terahertz Difference Frequencies by an Injection-Seeded Semiconductor Laser Amplifier at 850 nm

Two-frequency operation of an 850 nm semiconductor optical amplifier was achieved by simultaneously injection seeding it with two diode lasers. The two frequencies could be independently amplified without strong interference when they were separated by more than 10 GHz, and the spectral purity was preserved by the amplification process. At frequency differences below 10 GHz, unbalanced two-frequency output was observed, which can be explained by a two-mode interaction driven by the refractive index modulation at the beat frequency. The laser system is suitable for the difference-frequency generation of coherent terahertz radiation in ultra-fast photoconductors or nonlinear optical media.     

Crystallization of Arthrobacter sp. strain 1C N-(1-D-carboxyethyl)-L-norvaline dehydrogenase and its complex with NAD+

The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres.     

Irradiation of terephthalophenone in isopropyl alcohol

Irradiation of terephthalophenone in isopropyl alcohol gave a bright yellow-colored intermediate which decayed rather rapidly. The products were complex and depended upon the mode of irradiation. They ranged from a mixed polymer I to a dimer II. I consisted of about 5 terephthalophenone units capped with hydrogen or isopropyl alcohol radicals or terminated by cyclization. II, the dimer, was capped by hydrogen atoms.     

Synthesis of azaspirocyclic compounds via organoiron complexes. Potential synthetic routes to histrionicotoxin and cephalotaxus alkaloids.

Reaction of cyclohexadienylium-Fe(CO)₃ complexes (7) and (8) with sodiomalono-nitrile gives the carbo-spirocyclic derivatives (9) and (10), whilst reaction with benzylamine and removal of iron leads to the azaspirocyclic enones (15) and (16), respectively.