Novel ligands based on bromosubstituted hydroxycarbonyl [2.2]paracyclophane derivatives: synthesis and application in asymmetric catalysis

New planar-chiral hydroxycarbonyl [2.2]paracyclophane derivatives, 4-acetyl-13-bromo-5-hydroxy[2.2]paracyclophane (Br-АНРС, 63%) and 4-benzoyl-13-bromo-5-hydroxy[2.2]paracyclophane (Br-BHPC, 53%), were synthesized and reacted with the enantiomers of α-phenylethylamine to form corresponding Schiff bases, 12-bromo-4-hydroxy-5[1-(1-phenyl-ethylimino)-ethyl]-[2.2]paracyclophane and 12-bromo-4-hydroxy-5[1-(1-phenyl-ethylimino)-(phenyl)methylen-[2.2]paracyclophane. The diastereomers of the imines were resolved and their absolute configurations and consequently the corresponding configurations of the enantiomers of Br-АНРС were determined by X-ray diffraction. Enantiomerically pure Schiff bases were applied as ligands to form catalysts for the enantioselective addition reaction of diethylzinc with benzaldehyde where 1-phenylpropanol was obtained with 77–91% ee.

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(Rp)-1[13-Bromo-5-hydroxy[2.2]paracyclophane-4-yl)]ethanoneC18H17BrO2Ee >99%[α]D25=+363.3 (c 0.23, toluene)Source of chirality: (Rp,S)-12-bromo-5-hydroxy-4[1-(1-phenyl-ethylimino)-ethyl]-[2.2]paracyclophaneAbsolute configuration: (Rp)

(Rp,S)-12-Bromo-5-hydroxy-4[1-(1-phenyl-ethylimino)-ethyl]-[2.2]paracyclophaneC26H26BrNOEe >99%[α]D25=+872.0 (c 0.25, toluene)Source of chirality: resolutionAbsolute configuration: (Rp,S)

(Rp,S)-12-Bromo-4-hydroxy-5[1-(1-phenyl-ethylimino)-(phenyl)methylen]-[2.2]paracyclophaneC31H28BrNOEe >99%[α]D25=+555.0 (c 0.20, toluene)Source of chirality: resolutionAbsolute configuration: (Rp,S)

(Sp)-[5-Hydroxy[2.2]paracyclophane-4-yl)]phenylmetanonC23H20O2Ee >99%[α]D25=-254.4 (c 0.25, benzene)Source of chirality: (Sp,S)-4-hydroxy-5[1-(1-phenyl-ethylimino)-(phenyl)methylen]-[2.2]paracyclophaneAbsolute configuration: (Sp)

(Sp,S)-12-Bromo-5-hydroxy-4[1-(1-phenyl-ethylimino)-ethyl]-[2.2]paracyclophaneC26H26BrNOEe >99%[α]D25=-397.9 (c 0.33, toluene)Source of chirality: resolutionAbsolute configuration: (Sp,S)

(Sp,S)-12-Bromo-4-hydroxy-5[1-(1-phenyl-ethylimino)-(phenyl)methylen]-[2.2]paracyclophaneC31H28BrNOEe >99%[α]D25=-549.2 (c 0.20, toluene)Source of chirality: resolutionAbsolute configuration: (Sp,S)