Chemospecific Cyclizations of α-Carbonyl Sulfoxonium Ylides on Aryls and Heteroaryls

The functionalization of aryl and heteroaryls using α-carbonyl sulfoxonium ylides without the help of a directing group has remained so far a neglected area, despite the advantageous safety profile of sulfoxonium ylides. Described herein are the cyclizations of α-carbonyl sulfoxonium ylides onto benzenes, benzofurans and N-p-toluenesulfonyl indoles in the presence of a base in HFIP, whereas pyrroles and N-methyl indoles undergo cyclization in the presence of an iridium catalyst. Significantly, these two sets of conditions are chemospecific for each groups of substrates.

Synthesis of the tricyclic core of manzamine A

An approach to the ABC tricyclic ring system of the manzamine alkaloids has been achieved. A key step is the intramolecular dipolar cycloaddition of an azomethine ylide.

Clinical evaluation of Scotchbond: three-year results

In a previous paper, the one-year retention of composite resin in non-undercut Class V abrasion lesions mediated by self-cure Scotchbond dentine bonding agent without enamel etching was reported. The present paper reports the three-year results. Initially, a total of 310 restorations was placed using Silux, Silar, Ketac-Fil and Fuji II. The percentage cumulative loss of the restorations at two and three years, respectively, was: Silux 27, 30; Silar 58, 58; Ketac-Fil 0, 0; Fuji II 4, 14. Over the total study period, there was a high loss rate of composite restorations in the first six months, and a tendency to increased loss over one to three years. There was a significant increase in marginal discoloration, assessed photographically, over the three-year period, and caries was present around some restorations.

Syntheses and vibrational spectra of some tris(alkanethiolato)mercurate(II) complexes, and crystal structure of the Hexakis(methanethiolato)dimercurate(II) dianion

The complexes [cation] [Hg(SR)3](R = Me, cation = Et4N+; R = But, cation = Et4N+, Bu4N+, [N(Ph3P)2]+) have been prepared. The crystal structure of the methanethiolate complex shows that it contains centrosymmetric dinuclear anions [(MeS)2Hg(�-SMe)2Hg(SMe)2]2- with distorted tetrahedral geometry about the mercury atoms. Vibrational spectroscopic evidence suggests that this complex dissociates on dissolution in ethanol to give mononuclear [Hg(SMe)3]- species. The ButS- complexes appear to exist as mononuclear [Hg(SBut)3]- species both in the solid state and in solution. The metal-sulfur stretching frequencies are assigned for all of the complexes studied, and the vibrational spectra are discussed in terms of the structures of the complex anions involved. Crystal data for [(C2H5)4N]2Hg2(SCH3)6 : a 8.656(5), b gS130(6), c 12.368(8) �; α 102.16(4), β 105.51(4), γ 105.29(4)�; space group P1, Z 1, R 0.034, Rw 0.042.

Free-radical reductions of arenediazonium ions in aqueous solution. V. Pulse-radiolytic determination of rate constants for some para-substitutedbenzenediazonium ions

Some rate constants for the reduction of para-substituted benzenediazonium ions by the radicals eaq-, ·CH2OH, (CH3)2·COH and some semiquinone radical anions have been measured. The substituent group has no effect on the rates with eaq-, but as the reduction potential of the reducing radical becomes more positive, the substituent effect increases, electron-withdrawing groups enhancing the rates. No free halide is formed on reduction of p-BrC6H4N2+ or p-IC6H4N2+ by eaq- or ·CH2OH.

Free-radical reductions of arenediazonium ions in aqueous solution. IV. Kinetics of reactions of para-substituted diazonium ions with benzyl alcohol, isopropyl alcohol and methanol

Electron-withdrawing substituents are shown to increase the chain length of free-radical hydro-dediazoniation reactions, but the actual reaction step causing the substituent effect depends on the relative rates of propagation and termination reactions. With benzyl alcohol as reducing agent the rate of the slow propagation step is increased, while with isopropyl alcohol the rate of the termination step is decreased. Rate constants for some reactions of radicals with diazonium ions are reported, and the nature of some of these reactions and their implication for an understanding of the homolysis of aromatic diazo compounds are discussed.

Effect of specific growth limitations on cell wall composition of Staphylococcus aureus H

Conditions are described for the continuous culture of a derivative of Staphylococcus aureus H in a fully defined minimal medium in which cysteine is the sole amino acid. The effects of growth under various nutrient limitations on the composition and properties of the cell wall have been studied. The proportion of ribitol teichoic acid present in the wall, and the extent to which it is substituted with N-acetylglucosamine, varies in bacteria grown under different conditions as does the composition and extent of cross-linking of the peptidoglycan. Neither the derivative nor the original strain H produced teichuronic acid when grown under phosphate limitation.