Solid phase approaches to N-heterocycles using a sulfur linker cleaved by SmI2

A sulfur HASC (alpha-hetero-atom substituted carbonyl) linker has been utilized in solid-phase approaches to oxindoles and tetrahydroquinolones. The route to oxindoles employs the first Pummerer cyclizations on solid phase, whereas the route to tetrahydroquinolones involves a microwave-assisted Heck reaction followed by a Michael cyclization. In both cases, the linker is cleaved in a traceless fashion by electron transfer from samarium(II) iodide. The routes illustrate the compatibility of the linker system with a number of reaction types and its utility for library synthesis.     

Nitrogen NMR studies on some fused ring N-heterocycles

¹⁵N and¹⁴N NMR data are reported for a number of fused ring N-heterocycles.¹⁴N line widths,¹⁵N-¹H couplings and nitrogen shielding additivity rales are used for¹⁵N signal assignments. The results obtained lead to some progress in the generalization of the effects of nitrogen-nitrogen interactions on nitrogen shieldings.     

A quantitative N NMR investigation of tautomeric equilibria of two 1-hydroxybenzimidazoles

¹⁵N nuclear shielding data are used in a study of the tautomeric equilibria of two 1-hydroxybenzimidazoles. The nitrogen signal assignments are supported by INDO-S/SOS shielding calculations. The observation of the N-3 signal is shown to give a quantitatively reliable estimate of the position of equilibrium. In the unsubstituted 1-hydroxybenzimidazole the amount of the hydroxy from present in the equilibrium mixture is found to be proportional to the pK_a value of the solvent employed.     

A H and C NMR study of the prototropic equilibria of 2-indolinone

¹³C NMR data are reported for 0.5 M solutions in CDCl₃ of 2-indolinone and six related compounds. The question of prototropic equilibria is discussed involving three possible tautomers, A, B, C. Form A is found to predominate in the dynamic equilibria established for three of the compounds studied. In the case of a fourth compound slow exchange between forms B and C results in the finding of both of these forms in the approximate ratio 1:1.8. These findings are supported by ¹H NMR measurements. Corresponding ¹H and ¹³H C NMR measurements on methanol solutions are essentially the same.     

14N and 13C NMR of tautomeric systems of hydroxy-pyridines

¹⁴N NMR is shown to be an efficient method of investigation of the tautomeric equilibria in hydroxy-and related substituted pyridines. Large relative ¹⁴N chemical shifts within tautomeric pairs estimated from N-Me and O-Me derivatives make possible quantitative determinations of the equilibria. Qualitative conclusions may be drawn from ¹⁴N line widths as well as from ¹³C and proton chemical shifts.     

Measuring surface area of airborne titanium dioxide powder agglomerates: relationships between gas adsorption,diffusion and mobility-based methods

Inhalation toxicology studies generally use the Brunauer, Emmett, and Teller (BET) gas adsorption method to measure total surface area of particles whereas occupational exposures are more readily measured by real-time mobility-based surface areas or active surface area measured with diffusion charger-based instruments. Three surface area measurement methods were studied: filter-based inert gas adsorption (BET method), diffusion charging, and mobility-based methods. The goal of the project was to investigate and develop a correlation between the measurement methods. The experimental design consisted of measuring surface area in a series of five trials for each of two powder types, fine and ultrafine titanium dioxide with primary particle sizes of 440 and 20 nm, respectively, and two aerosol concentrations. Diffusion charger instruments tended to underestimate the total particle surface area measured by the BET, but were well correlated with mobility-based surface areas obtained from a scanning mobility particle sizer. Filter-based gas adsorption methods and diffusion charging methods provide different but valuable information on total and active surface areas of particles, respectively. Results indicate they should not be used as predictors of one another.     

119Sn NMR Spectra of Some Carbohydrate Organotin Derivatives

Abstract

The ¹¹⁹Sn NMR spectra of several sugar-tin derivatives were recorded. The geometric and steric isomers of all of the organotin derivatives studied were easily differentiated by ¹¹⁹Sn NMR. The appropriate ¹¹⁹Sn resonances are: ca - 50 ppm for trans and ?60 ppm for cis vinyltin derivatives (1-3), ca 16 ppm for allyltins 4-6, and ca ?32 ppm for tin-carbinols 9 and 11. When the hydroxyl group in carbinol 9 was converted to an O-acetyl group, the chemical shift of ¹¹⁹Sn was shifted to ?22 ppm.     

Polarity and Conformations of Phosphazacompounds in Solution

Abstract

A series of iminophosphoranes o-X-C₆H₄-N=PPh₃, where X=H(I),Me (II),Et (III),OMe(IV),OEt(V) were investigated by means of dipole moments method. Because of an orientation of aromatic fragment determines intramolecular interactions in the system (benzene ring - double N=P bond), the problem of internal rotation of N-C_ar bond is important. DM (exp.) of molecules (I-V), determined in dioxane are 4.30(I), 4.34(II), 4.53(III), 4.75(IV), 4.79 D(V), respectively.     

Solid-phase approach to tetrahydroquinolones using a sulfur linker cleaved by SmI2

[reaction: see text] A sulfur alpha-heteroatom-substituted carbonyl (HASC) linker has been utilized in a solid-phase approach to tetrahydroquinolones. The route illustrates the compatibility of the linker system with palladium-catalyzed transformations and its utility for library synthesis. The linker is cleaved by electron transfer from samarium(II) iodide.     

Mesoionic compounds — structure and NMR parameters

It has been shown that¹H,¹³C,¹⁴N,¹⁵N,¹⁷O, and⁷⁷Se NMR are very successful techniques for the identification and investigation of potential valence tautomerism in all types of mesoionic compounds. Especially the combined use of¹⁴N and¹⁵N NMR studies has been shown to be very effective in solving structural problems. From¹⁵N NMR it is possible to obtain accurate chemical shifts and spin-spin couplings, whereas the¹⁴N NMR spectra provide us with nuclear relaxation and some chemical shift data. In particular¹⁴N NMR is very useful for the identification of charged nitrogen atoms in molecules containing non equivalent nitrogen positions. This information is available from the relative¹⁴N signal widths, which depend upon the rates of¹⁴N relaxation, positively charged nitrogen atoms usually have relatively slow¹⁴N relaxation rates thus giving rather sharp NMR signals. Some solid state, CP MAS,¹³C and¹⁵N NMR results are available for comparison with the solution NMR data.Published in Khimiya Geterotsiklischeskikh Soedinenii, No. 9, pp. 1180–1199. September 1995.