(2S)-2-Anilinomethylpyrrolidine: an efficient in situ recyclable chiral catalytic source for the borane-mediated asymmetric reduction of prochiral ketones in refluxing toluene

(2S)-2-Anilinomethylpyrrolidine was successfully utilized as a chiral catalytic source in the borane-mediated asymmetric reduction of prochiral ketones in refluxing toluene to provide the corresponding secondary alcohols with enantiomeric excesses up to 91%. The potential of (2S)-2-anilinomethylpyrrolidine as an in situ recyclable chiral catalytic source in the borane-mediated chiral reduction processes has also been demonstrated.

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(S)-2-Bromo-1-phenylethanolC8H9OBrEe = 91%[α]D25=+39.8 (c 1.2, CHCl3)Source of chirality: asymmetric reductionAbsolute configuration: S

(S)-2-Chloro-1-phenylethanolC8H9OClEe = 87%[α]D25=+43.8 (c 1.0, cyclohexane)Source of chirality: asymmetric reductionAbsolute configuration: S

(S)-2-Chloro-1-(4-methylphenyl)ethanolC9H11OClEe = 84%[α]D25=+43.1 (c 0.8, CHCl3)Source of chirality: asymmetric reductionAbsolute configuration: S

(S)-2-Bromo-1-(4-bromophenyl)ethanolC8H8OBr2Ee = 90%[α]D25=+30.5 (c 1.0, CHCl3)Source of chirality: asymmetric reductionAbsolute configuration: S

(S)-2-Bromo-1-(4-chlorophenyl)ethanolC8H8OClBrEe = 90%[α]D25=+38.9 (c 0.9, CHCl3)Source of chirality: asymmetric reductionAbsolute configuration: S

(S)-2-Bromo-1-(4-nitrophenyl)ethanolC8H8NO3BrEe = 86%[α]D25=+29.9 (c 0.8, CHCl3)Source of chirality: asymmetric reductionAbsolute configuration: S

(R)-1-PhenylethanolC8H10OEe = 76%[α]D25=+35.2(c 0.9 MeOH)Source of chirality: asymmetric reductionAbsolute configuration: R

(R)-1-(4-Methylphenyl)ethanolC9H12OEe = 74%[α]D25=+33.1 (c 0.7, MeOH)Source of chirality: asymmetric reductionAbsolute configuration: R

(R)-1-(4-Bromophenyl)ethanolC8H9OBrEe = 78%[α]D25=+30.6 (c 1.0, CHCl3)Source of chirality: asymmetric reductionAbsolute configuration: R

(R)-1-(4-Chlorophenyl)ethanolC8H9OClEe = 77%[α]D25=+37.5 (c 0.7, Et2O)Source of chirality: asymmetric reductionAbsolute configuration: R

(R)-1-(4-Nitrophenyl)ethanolC8H9NO3Ee = 78%[α]D25=+22.2 (c 0.5, EtOH)Source of chirality: asymmetric reductionAbsolute configuration: R