Novel chiral tridentate Schiff base ligands of the [2.2]paracyclophane series: synthesis and application

The first example of the efficient application of chiral tridentate N,O-[2.2]paracyclophane ligands of the imino type for enantioselective diethylzinc addition to aliphatic and aromatic aldehydes is presented. The enantiomeric excess of the resulted secondary alcohols is up to 93% e.e.

GraphicFigure optionsDownload full-size imageDownload as PowerPoint slide

Schiff base of (S)-4-formyl-5-hydroxy[2.2]paracyclophane and ethanolamineC19H21NO2E.e. >99%[α]D22 −481.8 (c 0.23, CHCl3)Source of chirality: chiral starting materialAbsolute configuration: (Sp)

Schiff base of (R)-4-formyl-5-hydroxy[2.2]paracyclophane and (R)-valinolC22H26NO2E.e. >98%[α]D22 +653.5 (c 0.36, CH3OH)Source of chirality: chiral starting materialAbsolute configuration: (Rp,R)

Schiff base of (R)-4-acetyl-5-hydroxy[2.2]paracyclophane and ethanolamineC20H23NO2E.e. >99%[α]D22 +611.7 (c 0.21, CHCl3)Source of chirality: chiral starting materialAbsolute configuration: (Rp)

Schiff base of (R)-4-acetyl-5-hydroxy[2.2]paracyclophane and (S)-valinolC23H29NO2E.e. >99%[α]D22 653.5 (c 0.25, CHCl3)Source of chirality: chiral starting materialAbsolute configuration: (Rp,S)

Schiff base of (S)-4-acetyl-5-hydroxy[2.2]paracyclophane and (S)-valinolC23H29NO2E.e. >99%[α]D22 −603.8 (c 0.27, CHCl3)Source of chirality: chiral starting materialAbsolute configuration: (Sp,S)

Schiff base of (S)-4-acetyl-5-hydroxy[2.2]paracyclophane and (S)-leucinolC24H31NO2E.e. >99%[α]D22 −560.8 (c 0.22, CHCl3)Source of chirality: chiral starting materialAbsolute configuration: (Sp,S)

Schiff base of (R)-4-acetyl-5-hydroxy[2.2]paracyclophane and (S)-leucinolC24H31NO2E.e. >99%[α]D22 +646.8 (c 0.24, CHCl3)Source of chirality: chiral starting materialAbsolute configuration: (Rp,S)