Sodium Dithionite Reduction of 2S,5R-(-)-menthone and R-(+)-pulegone in the Presence of β-Cyclodextrin and Hydroxypropyl-β-cyclodextrin

Menthone on reduction with sodium dithionite,showed a good amount of mentholformation in the water/DMF system, withincreasing β-cyclodextrin (β-CD)concentration from 47.0% for 0.1 equivalent ofβ-CD to 93.5% for 1 equivalentof β-CD. Increasing hydroxypropyl-β-cyclodextrin(HPβ-CD) gave higher menthol/neomenthol (M/N) ratiosfrom 2.8 to 3.5. In the case of pulegone,increasing β-CD showed an increase in the formationof menthols in thewater/DMF system from 13.3% for 0.1 equivalent ofβ-CD to 78.1% for 1equivalent of β-CD with greater proportions ofneomenthol and neoisomenthol.However, HPβ-CD which showed only marginalenhancement in the formationof menthol from menthone (32.1–41%), exhibiteda greater proportion of mentholformation in the case of pulegone (55.1%).However, the phase-transfer capabilityof HPβ-CD was not found to be significant.