Plants-mediated reduction in the synthesis of homochiral secondary alcohols

The reduction of 5-hexen-2-one 1, 6-methyl-5-hepten-2-one 2, acetophenone 3, cis-bicyclo[3.2.0]hept-2-en-6-one 4 and 2-methylcyclohexanone 5 with various commercially available plants (i.e., Brassica oleracea botrytis, Cucurbita maxima, Cucurbita pepo, Cynara scolimus, Daucus carota, Foeniculum vulgare and Musa sapientum) is reported. In the reduction of ketones 1–3, both (S)- and (R)-enantiomers 6–8 were obtained in good yields and with appreciable enantiomeric excesses. With racemic ketones 4 and 5, both the diastereomeric endo/exo9 and 10 and cis/trans11 and 12 are produced with variable yields and enantiomeric excesses depending on the various plants used.

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5-Hexen-2-olC6H12OEe = 80% [by GLC analysis on a 25 m dimethyl-n-pentyl-cyclodextrin in OV 1701][α]D25=+10 (c 4.6, CHCl3)Source of chirality: plant reductionAbsolute configuration: S

6-Methyl-5-hepten-2-olC8H16OEe = 90% [by GLC analysis on a 25 m dimethyl-n-pentyl-cyclodextrin in OV 1701][α]D25=+13 (c 1.3, EtOH)Source of chirality: plant reductionAbsolute configuration: S

endo-Bicyclo[3.2.0]hept-2-en-6-olC7H10OEe = 85% [by GLC analysis on a 25 m dimethyl-n-pentyl-cyclodextrin in OV 1701][α]D25=+57 (c 1.1, CHCl3)Source of chirality: plant reductionAbsolute configuration: 1S,5R,6S

cis-2-MethylcyclohexanolC7H14OEe = 24% [by GLC analysis on a 25 m diethyl-tert-butylsilyl-cyclodextrin in OV 1701][α]D25=+5 (c 1, MeOH)Source of chirality: plant reductionAbsolute configuration: 1S,2R

trans-2-MethylcyclohexanolC7H14OEe = 92% [by GLC analysis on a 25 m diethyl-tert-butylsilyl-cyclodextrin in OV 1701][α]D25=+37 (c 9.6, EtOH)Source of chirality: plant reductionAbsolute configuration: 1S,2S

1-PhenylethanolC8H10OEe = 100% [by GLC analysis on a 25 m permethylated-cyclodextrin in OV 1701][α]D25=-43 (c 5.1, CHCl3)Source of chirality: plant reductionAbsolute configuration: S

exo-Bicyclo[3.2.0]hept-2-en-6-olC7H10OEe = 100% [by GLC analysis on a 25 m dimethyl-n-pentyl-cyclodextrin in OV 1701][α]D25=-91 (c 2.6, CHCl3)Source of chirality: plant reductionAbsolute configuration: 1R,5S,6S