Science of Synthesis

Venturello, P.; Barbero, M., Science of Synthesis, (2006) 8, 882.

The stereochemistry of the reduction of substituted cycloalkanones to produce a mixture of epimeric alcohols has been the subject of many studies. The reduction of menthone/isomenthone mixtures has been studied with different alkali metals in a variety of media. Since menthol is an important commercial product, it is necessary to prevent the reduction of menthone to neomenthol and also the epimerization of menthone to isomenthone. Several systems show good selectivity with yields of menthol ranging from 97% (Na in wet Et2O) to 82% (Na in MeOH). On the other hand, in the reduction of isomenthone to isomenthol the same systems show a scatter of results.[‌3‌] Sodium/alumina containing 25% sodium metal has been prepared.[‌4‌] This material has an excellent shelf life and it is found that an amount of reagent equivalent to 4.0 g atom equivalent of sodium per mole of the substrate is essential for complete conversion. In the case of the reduction of menthone (‌1A‌) and isomenthone (‌1B‌) (‌Scheme 2‌) the four isomers of menthol are obtained [menthol (‌2A‌), neomenthol (‌2B‌), isomenthol (‌2C‌), and neoisomenthol (‌2D‌) in the ratio 55:24:10:11].[‌3‌] A comparison of reductions with sodium/propan-2-ol and sodium/alumina/propan-2-ol shows that in most cases the sodium/alumina system furnishes relatively larger amounts of the unstable isomer.[‌4‌]

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References

Meeeeee Meeeeeeeeee

• 8.Meeeee-Meee, (8888) 8/8e, 888.
• 8.Meeeee-Meee, (8888) 8/8e, 888.
• 8.Meeeee-Meee, (8888) 8/8e, 888.