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Natural and unnatural aminoacids by catalytic reduction with Rh(I)-diphosphine complexes; role of strong acids in the synthesis of deuterium labelled histidine.
No full text
“In situ” Activation of Racemic RuII Complexes: Separation of trans and cis Species and Their Application in Asymmetric Reduction
Full text linkRuthenium(II) dichlorides with racemic atropos-biaryl-based diphosphanes and optically active 1,2-diphenylethane-1,2-diamine (DPEN) as ligands have been synthesised. trans and cis isomers were formed due to the low basicity of the diphosphane ligands, in particular, with BITIANP and BIMIP. The trans and cis species were easily separated by filtration. In particular, when rac-BITIANP was used in combination with chiral DPEN, the asymmetric separation of optically pure complexes in cis and trans arrangements was realised and they were used as precatalysts in the asymmetric hydrogenation of ketones. Matching and mismatching combinations exhibited different performances
Asymmetric Hydrogenation of prochiral Ketones catalyzed by Ru(II)Cl2diphosphine/diamine system
No full textcatalisi enantioselettiva : sintesi di istidina non naturale e istidina non naturale deuterata
No full textAminoquinoline-based Ruthenium catalyst for reduction of ketones by hydrogen transfer
No full textAsymmetric reduction of C=O and C=N bonds to give chiral alcohols and amines is one of the more relevant applications of transition metal catalysis1. A striking improvement in hydrogenation or reduction by hydrogen transfer is due to Noyori and more recently to Rigo and co-workers with the development of Ru(II) catalysts bearing chiral diamine ligands2.
Here we present our results in hydrogen transfer reduction of aryl ketones with (S)- or (R)-8-amino-5,6,7,8-tetrahydroquinoline (CAMPY).
We demonstrated that the enantiomers of CAMPYs were themselves possible alternatives to other diamines as ancillary ligands for AHT even with triphenylphosphine alone. CAMPYs, whose more relevant features are a flat scaffold and a rigid alkyl fused ring, gave highly efficient catalysts when combined with an achiral chelating diphosphine. We were able also to describe the three-dimensional structure of trans and cis-[RuCl2(CAMPY)PP] by 2D-NMR experiments and to define the chirality of the metal centre of the unique diastereoisomer coming from transcis isomerisation either when the phosphorous ligand was triphenylphosphine or chelating DPPB and DPPP.
We found a relationship between the ring size of the chelating diphosphines and the enantioselctivity of the catalysts, assigning to a six-member ring the best performances in term of activity and enantioselectivit
Histidine and deuterium labelled histidine by asymmetric catalytic reduction with gaseous H-2 or D-2 : the role of strong non-coordinating acids
No full textAn efficient and convenient route for the preparation of natural and unnatural hystidine by asymmetric hydrogenation with Rhodium-phosphine complexes is described. The reductions were performed in presence of HBF4 to generate essential imidazolyl cation. Stereoselective incorporation of D2 into the α,β-positions was obtained by catalytic deuteration in presence of MeOD
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