(5S)-1-Aza-2-imino-3-oxa-4,4-diphenylbicyclo(3.3.0)octane: a novel chiral catalytic source containing the N–(CNH)–O moiety for the borane-mediated asymmetric reduction of prochiral ketones

(5S)-1-Aza-2-imino-3-oxa-4,4-diphenylbicyclo(3.3.0)octane, a novel chiral catalytic source containing the N–(CNH)–O moiety, has been synthesized and successfully utilized, for the first time, as a chiral catalytic source in the borane-mediated asymmetric reduction of prochiral ketones in refluxing toluene, to provide the corresponding secondary alcohols with up to 93% enantiomeric excess.

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(5S)-1-Aza-2-imino-3-oxa-4,4-diphenylbicyclo(3.3.0)octaneC18H18N2O[α]D25=-221.9 (c 1.14, CHCl3)Source of chirality: (S)-2-(diphenylhydroxymethyl)pyrrolidineAbsolute configuration: (S)

(S)-2-Bromo-1-phenylethanolC8H9OBrEe = 92%[α]D25=+40.1 (c 1.8, CHCl3)Source of chirality: asymmetric reductionAbsolute configuration: (S)

(S)-2-Chloro-1-phenylethanolC8H9OClEe = 91%[α]D25=+44.7 (c 1.1, C6H12)Source of chirality: asymmetric reductionAbsolute configuration: (S)

(S)-2-Bromo-1-(4-bromophenyl)ethanolC8H8OBr2Ee = 92%[α]D25=+31.9 (c 1.2, CHCl3)Source of chirality: asymmetric reductionAbsolute configuration: (S)

(S)-2-Bromo-1-(4-chlorophenyl)ethanolC8H8OClBrEe = 93%[α]D25=+39.3 (c 1.0, CHCl3)Source of chirality: asymmetric reductionAbsolute configuration: (S)

(S)-2-Bromo-1-(4-nitrophenyl)ethanolC8H8NO3BrEe = 88%[α]D25=+32.3 (c 1.3, CHCl3)Source of chirality: asymmetric reductionAbsolute configuration: (S)

(R)-1-PhenylethanolC8H10OEe = 80%[α]D25=+35.5 (c 1.2, MeOH)Source of chirality: asymmetric reductionAbsolute configuration: (R)

(R)-1-(4-Methylphenyl)ethanolC9H12OEe = 70%[α]D25=+29.2 (c 1.5, MeOH)Source of chirality: asymmetric reductionAbsolute configuration: (R)

(R)-1-(4-Bromophenyl)ethanolC8H9OBrEe = 73%[α]D25=+27.5 (c 1.1, CHCl3)Source of chirality: asymmetric reductionAbsolute configuration: (R)

(R)-1-(4-Chlorophenyl)ethanolC8H9OClEe = 78%[α]D25=+38.5 (c 1.3, Et2O)Source of chirality: asymmetric reductionAbsolute configuration: (R)

(R)-1-(4-Nitrophenyl)ethanolC8H9NO3Ee = 87%[α]D25=+27.2 (c 1.2, EtOH)Source of chirality: asymmetric reductionAbsolute configuration: (R)