Modular Spiro Bidentate Nitrogen Ligands – Synthesis, Resolution and Application in Asymmetric Catalysis

A family of new modular, chiral, bidentate, nitrogen‐donor ligands containing the large spirobi(chroman) backbone 1 (SPAN) has been prepared. Enantiopure diamines containing the nitrogen donors at the 8,8′ positions of spirobi(chroman) 1 have been synthesized through the resolution of the 8,8′‐diamino racemate 3 . Accordingly, secondary and tertiary amines [(+)‐ 6 /(–)‐ 6 and (+)‐ 5 /(–)‐ 5 , respectively] and imino derivatives [(+)‐ 7 /(–)‐ 7 ] were obtained in both enantiomeric forms. A new SPAN derivative incorporating aldehyde groups at the 8,8′ positions of the spirobi(chroman) unit [(+)‐ 9 /(–)‐ 9 ] has been synthesized with the aim to extend the ligand library by means of Schiff base chemistry. The derivatization of the isolated enantiomers of 9 obtained by diastereomer resolution gave derivatives containing the nitrogen atoms at the benzylic positions. The syntheses of ligands (+)‐ 10 /(–)‐ 10 , (+)‐ 11 and (+)‐ 12 illustrate the scope of this methodology. The coordination ability of ligand (–)‐ 3 has been tested by the synthesis and characterization of complex [Pd(OAc) 2 {(–)‐ 3 }] [(–)‐ 13 ]. Some preliminary results related to the oxidative kinetic resolution of 1‐phenylethanol with this Pd complex are reported.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)