Ion-interaction chromatography of dithiocarbamates on βBondapak CN and LiChrosorb RP-8 stationary phases in the presence of tetraalkylammonium salts

Dithiocarbamates are examined by high-performance liquid chromatography on βBondapak CN and LiChrosorb RP-8 bonded phases using ion-interaction with tetraalkylammonium salts. The effects of the tetraalkylammonium cation and its inorganic co-anion on solute retention are considered. The response for sodium diethyldithiocarbamate is linear over the range 1–500 μg ml^?1, with a detection limit of 0.1 μ ml^?.     

The addition of methyllithium to 2,2,4,4-tetramethylcyclobutan-1-one-3-thione. The generation and capture of a bishomoenolate anion.

Methyllithium added to 2,2,4,4-tetramethylcyclobutan-1-one-3-thione to produce lithium 3-methylthio-2,2,4,4-tetramethylbicyclo[1.1.0]but-1-oxide. This bishomoenolate was alkylated on carbon by methyl iodide, but retained the bicyclo[1.1.0]butane skeleton when silated with chlorotrimethylsilane. The ease of oxidation of a series of 1,3-diheteroatom substituted bicyclo[1.1.0]butanes was determined.     

Synthesis of 2-methyl-D-erythritol via epoxy ester-orthoester rearrangement

The biomimetic epoxy ester[bond]orthoester rearrangement has been applied to a new synthesis of 2-methyl-D-erythritol, a branched five-carbon sugar of importance to the deoxyxylulose pathway of isoprenoid biosynthesis. The intermediate orthoacetate is one of the few [2.2.1]-orthoesters to have been reported. Labeling studies with O-18 indicated that this reaction proceeds exclusively via a 5-exo cyclization. NMR analysis of chiral esters indicated an ee of 87% for the starting epoxide and an ee of 86% for the product. This route represents a rapid and convenient method for the synthesis of 2-methyl-D-erythritol and is expected to be useful for generating isotopically labeled intermediates for biochemical studies.     

Electromagnetic field-induced protection of chick embryos against hypoxia exhibits characteristics of temporal sensing

We previously studied the response of mammalian cultured cells to weak, 60 Hz-electromagnetic (EM) fields. Two time constants, similar to those observed in chemotaxis, were found to govern the cellular response to the field. We concluded that a system of temporal sensing, similar to that employed in chemotaxis by motile bacteria, was operative. We termed the shorter time (approximately 0.1 s) the "sensing" time, and the longer time (approximately 10 s) the "memory" time. To investigate the possibility that temporal sensing was a general property of EM field-cell interaction, the temporal properties of another EM field-induced effect was studied. The EM field-induced protection against the effects of extreme hypoxia was examined in chick embryos. Embryos were exposed to 60 Hz-magnetic fields, the amplitudes of which were regularly altered throughout the 20-min exposure. Alteration was accomplished either by turning the field off and on at regular intervals (1-50 s), or by introducing brief (10 or 100 ms), zero amplitude gaps, once each second, throughout exposure. When the field was turned on and off at 0.1 s intervals, the protective effect conferred by a constant field was lost. At progressively longer on/off intervals, protection was progressively restored, maximizing at intervals of 10-30 s. Gapping the magnetic field for 10 ms, each second of exposure conferred the same protection as that observed for an uninterrupted field, but gapping the field at 100 ms each second produced a significant reduction in protection. These data exhibit remarkable consistency with those obtained in similar temporal studies of the magnetic field-induced enhancement of ornithine decarboxylase activity in L929 fibroblasts. It appears that temporal sensing is a general feature of the EM field-cell interaction.     

Syntheses of perfluorinated epoxides,diepoxides, and a novel rearrangement

t-Butylhydroperoxide/butyl-lithium is a good reagent for synthesis of epoxides and diepoxides from polyfluorinated-alkenes and-polyenes. This reagent and calcium hypochlorite both give a novel diepoxide 5 from perfluoro-3,4-dimethyl-2,4-diene 1; diepoxide 5 undergoes a novel rearrangement, at 200°C, to the corresponding 1,4-dioxine derivative 18. Possible mechanisms are discussed.     

Synthesis and oxygenation of a nickel(II) and zinc(II) dithiolate: an experimental and theoretical comparison

The diamino-dithiolato N2S2 ligand N,N'-bis-2-methyl-mercaptopropyl-N,N'-dimethylethylenediamine, H2bmmp-dmed), and its nickel (1) and zinc (2) complexes have been prepared and their reactivities with hydrogen peroxide investigated. Complex 1 yields a mixture of sulfenato (RSO-), 4, sulfinato (RSO2-), 3, and sulfonato (RSO3-), 5, products upon addition of H2O2. Products are separable by column chromatography. Stoichiometric addition of H2O2 to 2 yields an inseparable mixture. Excess peroxide addition results in oxygenation of the ligand to the disulfonate, 6, and decomplexation of zinc. Complexes 1, 2, and 3 and compound 6 have been investigated by X-ray crystallography, and their structures are reported. Density functional theory (DFT) calculations of 1 and 2 reveal significant sulfur p character in the HOMO of each complex. However, 1 also shows significant metal d character that is pi-antibonding with respect to the sulfur p orbitals. Complex 2 shows little metal character in the HOMO. Implications of the HOMO with respect to S-centered reactivity and metal ligand distances in S-oxygenated products are provided.     

C−H Activation of Inert Arenes using a Photochemically Activated Guanidinato-Magnesium(I) Compound

UV irradiation of solutions of a guanidinate coordinated dimagnesium(I) compound, [{(Priso)Mg}₂] 3 (Priso=[(DipN)₂CNPrⁱ₂]⁻, Dip=2,6-diisopropylphenyl), in either benzene, toluene, the three isomers of xylene, or mesitylene, leads to facile activation of an aromatic C−H bond of the solvent in all cases, and formation of aryl/hydride bridged magnesium(II) products, [{(Priso)Mg}₂(μ-H)(μ-Ar)] 4 – 9 . In contrast to similar reactions reported for β-diketiminate coordinated counterparts of 3 , these C−H activations proceed with little regioselectivity, though they are considerably faster. Reaction of 3 with an excess of the pyridine, p-NC₅H₄Bu^t (py^But), gave [(Priso)Mg(py^ButH)(py^But)₂] 10 , presumably via reduction of the pyridine to yield a radical intermediate, [(Priso)Mg(py^But⋅)(py^But)₂] 11 , which then abstracts a proton from the reaction solvent or a reactant. DFT calculations suggest two possible pathways to the observed arene C−H activations. One of these involves photochemical cleavage of the Mg−Mg bond of 3 , generating magnesium(I) doublet radicals, (Priso)Mg⋅. These then doubly reduce the arene substrate to give “Birch-like” products, which subsequently rearrange via C−H activation of the arene. Circumstantial evidence for the photochemical generation of transient magnesium radical species includes the fact that irradiation of a cyclohexane solution of 3 leads to an intramolecular aliphatic C−H activation process and formation of an alkyl-bridged magnesium(II) species, [{Mg(μ-Priso^−H)}₂] 12 . Furthermore, irradiation of a 1 : 1 mixture of 3 and the β-diketiminato dimagnesium(I) compound, [{(^DipNacnac)Mg}₂] (^DipNacnac=[HC(MeCNDip)₂]⁻), effects a “scrambling” reaction, and the near quantitative formation of an unsymmetrical dimagnesium(I) compound, [(Priso)Mg−Mg(^DipNacnac)] 13 . Finally, the EPR spectrum (77 K) of a glassed solution of UV irradiated 3 is dominated by a broad featureless signal, indicating the presence of a doublet radical species.