1,721,203 research outputs found
Configurational and conformational analysis of silyl ketene thioacetals by NMR spectroscopy and computational studies
No full textThe configuration and conformation of silyl ketene thioacetals derived from 2-pyridyl thioesters were studied by combined NMR and computational analysis. The results revealed that the (E)-silyl ketene thioacetal is always the thermodynamically favoured diastereoisomer; the equilibrium ratio is reversed /E/Z>2:98/ for steric reasons when two O-silyl substituents are present on the C=C double bond, The preferred conformational minima for the E and Z isomers are proposed on the basis of Monte Carlo conformational searches performed on selected model compounds; the computational results are in excellent agreement with the NMR data
Asymmetric induction in the reduction of beta-oxosulphoximides by sodium borohydride
No full textOptically active β-oxosulphoximides have been prepared by reaction of optically active α-metallated NS-dimethyl-S-phenylsulphoximide with carboxylic esters. Their reduction by sodium borohydride is stereoselective, the extent of asymmetric synthesis (up to 50%) depending on steric factors
Enantiomeric excess determination of new classes of chiral sulphur compounds by the use of europium reagents
No full textThe enantiomeric composition of derivatives of new classes of optically active sulphur compounds (variously substituted sulphoxides, sulphoximes, sulphilimines) has been readily determined with the aid of chiral europium shift reagents
Mild synthesis of enantiomerically pure imidazo-[1,2-a]azepines mediated by Yb(OTf)(3)
No full textThe reaction of various chiral 2,2'-diaryldialdehydes with achiral and chiral 1,2-diamines in the presence of Lewis acids to give imidazo[1,2-a]azepines was investigated. Best results were achieved with Yb(OTf)(3); the reaction outcome is strongly dependent upon the geometric features of both reactants. Kinetic resolution of rac-2,2'-dinaphthyldialdehyde with (R,R)-1,2-diphenyl-1,2-diamminoethane (up to 92% e.e.) was achieved. (C) 2001 Elsevier Science Ltd. All rights reserved
Asymmetric induction in the reduction of optically active N-alkylidenesulphinamides by metal hydrides. A new efficient enantioselective route to chiral amines
No full textA series of racemic and optically active N-alkylidenesulphinamides has been prepared and their reduction by metal hydrides studied. The extent of asymmetric synthesis mainly depends on the nature of the reducing species; the best results (up to 92% of stereoselectivity) are obtained with alkoxy-lithium aluminium hydrides. A new, highly enantioselective synthesis of amines is described
Asymmetric induction in the reduction of beta-oxosulphoxides by metal hydrides
No full textA series of optically active β-oxosulphoxides has been prepared and their reduction by metal hydrides examined; when lithium aluminium hydride is used, the extent of asymmetric synthesis is in the range 60-70%
Stereospecific and stereoselective synthesis of beta-oximino and beta-hydroxylamino sulphoxides
No full textCatalytic, enantioselective allylation of alfa-iminoesters promoted by Silver(I) complexes of chiral imines
No full textThe catalytic enantioselective addition of allyltributylstannane to N-protected greek small letter alpha-iminoesters promoted by silver(I) trifluoromethanesulfonate in the presence of chiral imine ligands was studied. After testing several chiral imines derived from 1,2-diaminocyclohexane and binaphthyl diamine a very simple experimental procedure was developed that allowed us to obtain optically active homoallylic amines in very high yields and enantioselectivities up to 71%
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