Efficient and stereoselective synthesis of (S)-α-propargylglycine derivatives from allenylboronic acid

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A note on the positive solutions of second order differential equations

We obtain an existence theorem for monotone positive solutions of nonlinear second-order nonlinear differential equations via principal and nonprincipal solutions of the corresponding homogeneous equation.     

Trifluoromethylated cyclopropanes and epoxides from CuI-mediated transformations of α-trifluoromethyl-diazophosphonate

An efficient method for the preparation of α-(trifluoromethyl)-cyclopropylphosphonates and α-(trifluoromethyl)-1,2-epoxyphosphonates has been developed. The method is based on metal-catalyzed reaction of diethyl 1-diazo-2,2,2-trifluoroethylphosphonate (1) with alkenes or carbonyl compounds, respectively. It established an essential advantage of CuI-catalysis over Rh₂(OAc)₄ in cyclopropanation reactions. An inexpensive copper iodide has also exhibited a good catalytic activity in the synthesis of epoxyphosphonates (3).     

Preparative procedure of dihalosulfenylation: Thiobisamines addition to unsaturated compounds in the presence of phosphorus oxyhalides and halides

A new synthetic method was developed for \,\′-dihaloalkyl sulfides (halogen chlorine or bromine) by reaction of thiobisamines with olefins and alkynes in the presence of the appropriate phosphorus halides. The reaction proceeds along electrophilic mechanism affordingtrans-addition products. The highest yields of the target products were obtained at POBr₃ or POC1₃ application. The study was carried out under financial support of the Russian Foundation for Basic Research (grant no. 99-03-33093).     

New carborane-containing amino acids and their derivatives. Crystal structures of <Emphasis Type="Italic">n</Emphasis>-protected carboranylalaninates

New alanine derivatives containing both the carboranyl and trifluoromethyl groups were synthesized by the reaction of organometallic derivatives of o-carborane with methyl trifluoropyruvate imines. When using the 1R-(−)-menthoxycarbonyl protecting group at the nitrogen atom, one of diastereomers was isolated and characterized. Trifluoromethyl-carboranylalanine methyl esters containing different protecting groups at the nitrogen atom were studied by X-ray diffraction. Both complete and partial deprotection of the amino and carboxy groups was performed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 761–767, April, 2007.     

An approximate treatment of scattering based on the delta boundary operator

The development of a scheme to treat two-dimensional electromagneticscattering by electrically large, perfectly conducting bodiesis described. It incorporates the effects of surface curvatureand non-local phenomena and has the potential to provide thebasis for a general technique yielding more accurate predictionsthan the widely used physical optics method.