Abstract
The synthesis of P-stereogenic bisphosphine ligands starting from a phosphinous acid chiral synthon and hydrazine is reported. The dialkylation of the hydrazine backbone yielded atropo- and nitrogen inversion isomers which are in slow exchange. The crystallization of one of the isomers allowed us to study the reaction kinetics of the equilibria. The new ligands were tested in the Rh catalysed asymmetric hydrogenation of various benchmark substrates attaining up to 99% ee.
Highlights
The synthesis of P-stereogenic bisphosphine ligands starting from a phosphinous acid chiral synthon and hydrazine is reported
The dialkylation of the hydrazine backbone yielded atropo- and nitrogen inversion isomers which are in slow exchange
The new ligands were tested in the Rh catalysed asymmetric hydrogenation of various benchmark substrates attaining up to 99% ee
Summary
The synthesis of P-stereogenic bisphosphine ligands starting from a phosphinous acid chiral synthon and hydrazine is reported. The dialkylation of the hydrazine backbone yielded atropo- and nitrogen inversion isomers which are in slow exchange. Our group has recently reported procedures for the synthesis of optically pure P-stereogenic tert-butylmethylphosphinous acid borane 1.7 This fragment is highly versatile and has allowed access to C1 symmetric MaxPHOS8 and MaxPHOX9 ligands.
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