Stereoselective reduction of menthone with sodium dithionite in the presence of β-cyclodextrin

The effect of β-cyclodextrin (BCD) and its methyl and polymer derivatives on the stereoselective reduction of menthone was studied. Modification of the yield and the proportion of epimeric alcohols formed were found to be the salient features of this reaction. Reduction of menthone in aqueous solution in presence of heptakis-2,6-di-O-methyl-β-cyclodextrin (DMBCD) remarkably enhanced the yield to 68% (from 10%) resulting in a menthol/neomenthol ratio of 1:2.5. Aqueous DMF (1:1) as the solvent increased the yield from 14.0% in water to 76% in the presence of BCD, the menthol/neomenthol ratio being 1:3.6. Under phase transfer condition, DMBCD in water—benzene mixture gave 82.0% yield along with a good stereoselectivity compared to 47.0% in the absence of a phase transfer catalyst.