Phosphoramidite ligands for the enantioselective iridium-catalyzed asymmetric hydroboration of meso-bicyclic hydrazines

Twenty phosphoramidites or phosphite ligands have been screened in the iridium-catalyzed hydroboration of a meso-bicyclic hydrazine. Enantiomeric excesses of up to 67% could be obtained with moderate to good yields. Although bidentate ligands are believed to be more efficient in transition metal-catalyzed asymmetric hydroboration, this study shows that monodentate ligands have to be investigated for further development of this type of reaction.

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5-Hydroxy-2,3-diazabicyclo[2.2.1]heptane-2,3-dicarboxylic acid dibenzyl esterC21H22N2O5Ee = 67%[α]D30=-7.55 (c 1.06, CH2Cl2)Source of chirality: asymmetric catalysisAbsolute configuration: (1S,4R,5R)