NaBH3CN and other systems as substitutes of tin and silicon hydrides in the light or heat-initiated reduction of halosugars: a tunable access to either 2-deoxy sugars or 1,5-anhydro-itols

UV light-promoted reduction of acetobromoglucose by NaBH₃CN in t-BuOH afforded 1,3,4,6-tetra-O-acetyl-2-deoxy-α-d-arabino-hexopyranose in high yield and purity, via a Surzur–Tanner rearrangement, while, with 10 mol % thiophenol added, acetylated 1,5-anhydro-d-glucitol was cleanly obtained. Such tin-free and mild reductions, presumed to proceed via radical pathways, were more efficient with NaBH₃CN compared to NaBH₄ or NaBD₄, and do not occur with acetochloroglucose. Similar reductions to 1,3,4,6-tetra-O-acetyl-2-deoxy-α-d-arabino-hexopyranose were achieved upon heating to 80 °C t-BuOH or CH₃CN solutions of NaBH₃CN and AIBN, but with a lower selectivity due to competing ionic reactions. With other pyranosyl bromides, reductions by NaBH₃CN could be tuned similarly (d-galacto), but some (d-manno, 5-thio-d-xylo) gave mainly or exclusively 1,5-anhydro-itols. Other conditions, or reagents promoting SET process, afforded also reduced products, but with lower rates or selectivities. Primary iodides were reduced readily with NaBH₃CN under UV light.     

Thio Analogs of Pyrimidine Bases: Synthesis And Spectroscopic Study of New Potentially Biologically Active Disulfides of N,O-(N,N- or O,O-)-Di- and N,N,O-Tri-(o-, m-, and p-)bromobenzyl-2-thiouracils

Nine new disulfides of N,O-(N,N- or O,O-)-di- and N,N,O-tri-(o-, m- and p-)bromobenzyl-2-thiouracils have been prepared. The structures of these compounds were confirmed by spectroscopic (FT-IR, UV-Vis, ¹H NMR) and elemental analyses. Estimation of pharmacotherapeutic potential has been made for synthesized compounds on the basis of Prediction of Activity Spectra for Substances (PASS).     

Reaction of α,α-, α,α′-dihalothiones with 8-mercaptoquinolinium halides as a route to tetrahydro-1,4-thiazinoquinolinium halides

The reaction of 8-mercaptoquinolinium bromide with 1,3-dibromopropane-2-thione or 3,3-dibromobutane-2-thione in methanol gave the 2-bromomethyl-2-mercaptotetrahydro-1,4-thiazino[2,3,3,4-i,j]quinolinium and 3-bromo-2-mercapto-2,3-dimethyltetrahydro-1,4-thiazino[2,3,3,4-i,j]quinolinium bromides which readily exchanged the Br⁻ anion for ClO ₄ ⁻ upon treatment with sodium perchlorate in methanol. Oxidation of the 3-bromo-2-mercapto-2,3-dimethyltetrahydro-1,4-thiazino[2,3,3,4-i,j]-quinolinium bromide by selenium dioxide gave 2,2-dithiobis(3-bromo-2,3-dimethyltetrahydro-1,4-thiazino[2,3,3,4-i,j]quinolinium) bromide. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1720–1723, November, 2006.     

Bromine atom diffusion on stepped and kinked copper surfaces

The rates of Br atom diffusion on several single crystalline Cu surfaces have been studied because of the potential impact of Br diffusion on the selectivity of alkyl bromide surface chemistry on Cu. Density functional theory (DFT) has been used to study the diffusion of isolated bromine atoms on a flat Cu surface, Cu(1 1 1), two Cu surfaces with straight steps, Cu(2 2 1) and Cu(5 3 3), and two kinked Cu surfaces, Cu(6 4 3) and Cu(5 3 1). Bromine diffusion is rapid on the flat Cu(1 1 1) surface with a barrier of ΔE_diff = 0.06 eV and a hopping frequency of ν = 4.8 × 10¹⁰ s⁻¹ at 150 K. On the stepped and kinked surfaces the effective diffusion barriers lie in the range ΔE_diff = 0.18-0.31 eV. Thus the rates of diffusion are many orders of magnitude slower on stepped and kinked Cu surfaces than on the Cu(1 1 1) surface. Nonetheless, at temperatures relevant for alkyl bromide debromination on Cu surfaces, bromine atoms remain sufficiently mobile that they can explore all available binding sites on the timescale of the debromination reaction.     

Luminescence of Ce in hydrated rare earth bromides

Intense photoluminescence is reported for hydrated bromides of Gd, La and Y (LaBr₃·7H₂O, CeBr₃·7H₂O, YBr₃·8H₂O and GdBr₃·n H₂O) prepared by the wet chemical method and activated with Ce³⁺. Intensities are comparable to that for a commercial phosphor (SrB₄O₇:Eu²⁺—Sylvania 2052). Luminescence in hydrated salt is usually quenched. The observation of intense luminescence in hydrated bromides is remarkable.     

Synthesis of cinnamyl substituted dihydrofuranones by the Heck cross-coupling reaction

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Benzylic bromination catalyzed by triphenylphosphine selenide via Lewis basic activation

The synthesis of benzyl bromides was achieved under mild reaction conditions using N-bromosuccinimide as a bromine source and triphenylphosphine selenide as a catalyst. These conditions were compatible with a variety of substrates including boronic esters, protected amines to give imines, and carboxylic acids (to give phthalides when ortho to the benzylic center). A preliminary mechanistic investigation utilizing calculated bond dissociation energies (BDE) is employed to rationalize how a Lewis base can activate a radical mechanism.     

The investigations in 2,3′-biquinoline series. 25*. Synthesis of 4-(2-quinolinyl)-pyrrolo[1,2-<Emphasis Type="Italic">a</Emphasis>]quinolines and 4-(2-quinolyl)-imidazo[1,2-<Emphasis Type="Italic">a</Emphasis>]quinolines

A method has been developed for the synthesis of 4-(2-quinolinyl)-1,2,3,3a-tetrahydropyrrolo-[1,2-a]quinolines based on the 1,3-dipolar cycloaddition reaction of α,β-unsaturated carbonyl compounds to 2,3′-biquinolinium salts. Oxidation in benzene using MnO₂ gave 4-(2-quinolinyl)-pyrrolo[1,2-a]quinolines. It was found that a side product of the 1,3-dipolar cycloaddition is 7,14-di-benzoyl-6,13-di(2-quinolyl)-6a,7,13a,14-tetrahydro-7a,14a-diazadibenzo[a,h]anthracene. Reaction of 1′-phenacyl-2,3′-biquinolinium salts with hydroxylamine in acetic acid gave 4-(2-quinolyl)imidazo-[1,2-a]quinolines. *For Communication 24 see [1]. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 433–439, March, 2009.