Menthofuran is an organic compound found in a variety of essential oils including that of pennyroyal (Mentha pulegium).

It is highly toxic and believed to be the primary toxin in pennyroyal responsible for its potentially fatal effects.

Menthofuran can be synthesized from 5-methylcyclohexane-1,3-dione and allenyldimethylsulfonium bromide in two steps via a furannulation strategy consisting of enolate addition and rearrangement.

Both in vitro and in vivo studies have found the pulegone metabolite menthofuran to be an inhibitor of CYP2A6.

[4][5][6][7] Menthofuran may deplete glutathione levels, leaving hepatocytes vulnerable to free radical damage.